Method for evaluating degradation of a photodetector

Abstract

A method for evaluating degradation of a photodetector (112), the photodetector (112) comprising at least one photosensitive element (116), the photodetector (112) being configured for generating at least one detector current depending on an illumination of the photosensitive element (116) by light, the photodetector (112) further comprising at least one evaluation unit (120) for evaluating the detector current, wherein method comprises: a) determining at least one detector current; b) evaluating the detector current with respect to at least one reference value to obtain at least one relative detector current value; and c) deriving at least one item of degradation information on the photosensitive element (116) using the relative detector current value, the item of degradation information describing the degradation of performance due to temperature hysteresis behavior, aging, excessive temperatures and / or excessive illumination.

Description

[0001] Method for evaluating degradation of a photodetector

[0002] Technical Field

[0003] The invention relates to a method for evaluating degradation of a photodetector, a photodetector and a spectrometer device comprising the photodetector. The present invention further relates to a computer program and a computer-readable storage medium for performing the method. Such devices and methods can, in general, be used for investigating or monitoring purposes, in particular, in the infrared (IR) spectral region, especially in the near-infrared (NIR) spectral region, and in the visible (VIS) spectral region, e.g. in a spectral region allowing to mimic a human's ability of color sight. However, further applications are feasible.

[0004] Background art

[0005] Spectrometer devices are known to be efficient tools for obtaining information on the spectral properties of an object, when emitting, irradiating, reflecting and / or absorbing light. Spectrometer devices, thus, may assist in analyzing samples or other tasks in which information on the spectral properties of an object is of interest.

[0006] Usually, in spectrometer devices, spectral information is obtained via one or more detectors and one or more wavelength-selective optical elements, such as one or more dispersive optical elements, filters such as bandpass filters, prisms, gratings, interferometers, or the like. Spectrometer devices may further comprise one or more light sources. Thus, in spectroscopy, typically, tunable light sources, e.g. lasers, and / or broadband emitting light sources are used, such as halogen-gas filled light bulbs and / or hot filaments. However, additionally or alternatively, other light sources, such as light-emitting diodes have also been proposed for the visible spectral region. The detectors of the spectrometer device may comprise any type of light-sensitive element, such as one or more single or multiple pixel detectors, line detectors or array detectors having one- or two-dimensional arrays of pixels. These detectors may generate charge carriers due to an illumination by light, which is known as the photoelectric effect, and, thus, usually represent photodetectors.

[0007] In general, photodetectors, such as photodiodes and / or photoresistors, may be configured for detecting optical signals via a change of a detector current. A performance of the photodetectors may generally change with their temperature. Specifically, detector signals of infrared photodetectors may suffer from a temperature increase due to thermally activated charge carriers and / or traps in the light-sensitive material of the photodetector. The thermally activated charge carriers and / or traps may have a significant lifetime and, thus, photodetectors may exhibit temperature hysteresis, i.e. photodetectors may show thermally degraded performance over a time span after are returning to a lower temperature. Further, photodetectors, specifically photodetectors based on semiconductor devices, may exhibit aging, i.e. a degradation of performance over usage time. Further, also excessive temperatures and / or excessive illumination of photodetectors may cause a degradation of the performance of photodetectors. The degradation of performance due to temperature hysteresis aging, excessive temperatures and / or excessive illumination may render a photodetector unusable and / or change the characteristics of the photodetector such that the photodetector generates erroneous measurements without renewed calibration. This is especially critical for spectroscopic systems using multiple photodetectors that may experience aging and / or hysteresis differently.

[0008] KR 2019 0107123 A1 discloses a method of monitoring time-varying fluorescence emitted from a fluorescent agent within a diffusely reflecting medium having time-varying optical properties, comprising the steps of providing a measurement data set comprising a plurality of measurement entries. Each measurement data entry comprises at least two measurements acquired at one data acquisition time from a patient before and after administration of the fluorescent agent. The step comprises detecting a Flrmeas-signal adjacent to the diffusely reflecting medium by a filtered photodetector during illumination of the diffusely reflecting medium with light of an excitation-wavelength and at least one DR signal selected from: DRem-signal, and DRem,fiitered-signal. The method further comprises the steps of identifying a post-equilibrium portion of the measurement data set and converting each Flrmeas-signal of each measurement data entry in the postequilibrium portion of the measurement data set into an I Fagent-signal representing a detected fluorescence intensity emitted only by the fluorescent agent within the diffuse reflecting medium. The method comprises the steps of removing the effect of leakage of excitation light and removing the effect of spontaneous fluorescence from the Flrmeas-signal.

[0009] US 2013 / 015331 A1 describes a device for detecting light including at least one silicon photomultiplier (SiPM) having an array of a plurality of single-photon avalanche diodes (SPADs), the array being larger in area than an incident light. The device is configured so as to at least one of activate and analyze only the SPADs upon which a specific minimum intensity of light impinges.

[0010] US 2014 / 268136 A1 discloses a method and an apparatus for correcting a spectrometer system for light source quality, exposure time, distortion in y direction, distortion in x direction, temperature dependence, pixel alignment variability, dark pixels, bad pixels, pixel read noise, and pixel dark current noise. The method and apparatus produces an algorithm for optimizing spectral data and for measuring a sample within the spectrometer system using the optimization algorithm. The spectrometer apparatus comprises a composite external light source, a source light collector, an illumination light structuring component, a sample, a sample light collector, a spectrometer light structuring component, a light dispersing engine, photo detectors, an electrical signal converter, a data preprocessing unit, and a data analyzer. The method and apparatus can include a corrected photo detector algorithm, sample illumination correction algorithm, LDE- PD alignment procedure, SLSC-LDE alignment procedure, distortion correction matrix, and an algorithm for optimizing of spectral data.

[0011] Despite the advantages achieved by known methods and devices, several technical challenges remain. Specifically, degradation of photodetectors due to aging and / or temperature hysteresis may render photodetectors temporarily unusable and may lead to generation of erroneous measurements. Thus, generally, there is a need for monitoring photodetectors on a regular basis. For photodetectors used in industrial products, monitoring of the photodetectors may be both cost- and time-consuming. For photodetector used in consumer products, monitoring of the photodetectors by means of user action may generally be challenging, specifically with respect to reliability. Therefore, monitoring of the photodetector may have to be performed during normal usage of the photodetector. Furthermore, as servicing is not economically viable, the degraded performance of the photodetector needs to be calibrated.

[0012] Problem to be solved

[0013] It is therefore desirable to provide methods and devices which at least partially address above- mentioned technical challenges. Specifically, a method for evaluating degradation of a photodetector and a photodetector shall be proposed which allow monitoring the degradation of photodetectors with minimal additional hardware effort and low expenses with regard to cost and time.

[0014] Summary

[0015] This problem is addressed by a method for evaluating degradation of a photodetector, a photodetector and a spectrometer device comprising the photodetector, and a computer program and a computer-readable storage medium for performing the method, with the features of the independent claims. Advantageous embodiments which might be realized in an isolated fashion or in any arbitrary combinations are listed in the dependent claims as well as throughout the specification.

[0016] In a first aspect of the present invention, a method for evaluating degradation of a photodetector, specifically of a photosensitive element comprised by the photodetector, is disclosed. The term “photodetector” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an arbitrary device configured for detecting, i.e. for at least one of determining, measuring and monitoring, at least one parameter, qualitatively and / or quantitatively, such as at least one of a physical parameter, a chemical parameter and a biological parameter. The photodetector may specifically be configured for detecting the at least one parameter using the photoelectric effect, the parameter specifically being an optical parameter, such at least one parameter of light. The photodetector may be configured for generating at least one detector signal, more specifically at least one electrical detector signal, such as an analogue and / or a digital detector signal, the detector signal providing information on the at least one parameter measured by the photodetector. The detector signal may specifically comprise at least one detector current indicating an accumulated photocurrent from the photodetector, specifically at least one detector current from each pixel or element of the photodetector. The detector signal may directly or indirectly be provided by the photode- tector to an evaluation unit, as will be outlined in further detail below, such that the photodetector and the evaluation unit may be directly or indirectly connected. The detector signal may be used as a “raw” detector signal and / or may be processed or preprocessed before further used, e.g. by filtering and the like. Thus, the photodetector may comprise at least one processing device and / or at least one preprocessing device, such as at least one of an amplifier, an ana- logue / digital converter, an electrical filter and a Fourier transformation.

[0017] The term “degradation” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a change of at least one state or property of a device with respect to a known or predetermined standard state or property. Specifically, the degradation of a device may comprise a deterioration in quality, level and / or performance of at least one functionality of the device. For example, the degradation of the photodetector may comprise a deterioration of a performance of the photodetector of detecting light, e.g. a decrease in a sensitivity of the photodetector for detecting light. The degradation may be caused by internal influences, such as aging, and / or external influences, such as environmental influences, e.g. a change in ambient temperature, humidity and / or illumination. The degradation may comprise a reversible change of the at least one state or property, e.g. a temporary change, or an irreversible change, e.g. a persistent change. The irreversible change may also be referred to as a defect of the device.

[0018] The term “evaluating” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a process of assessing at least one state or property of a device. The evaluating may comprise one or more processing steps comprising processing at least one item of information on the device or generated by the device in order to assess the state or property of the device. The evaluating may specifically comprise generating at least item of information indicative of the state or property of the device. For example, the evaluating of the degradation of the photodetector may comprise processing one or more items of information, such as one or more items of information on the photodetector or any part thereof, in order to assess the degradation of the photodetector or any part thereof. The evaluating of the degradation may specifically comprise monitoring degradation of the photodetector or any part thereof over a period of time, such as during usage of the photodetector. The evaluating of the degradation of the photodetector may comprise indicating a change of the at least one state or property of the photodetector or any part thereof with respect to a known or predetermined standard state or property.

[0019] The photodetector comprises at least one photosensitive element. The photodetector is configured for generating at least one detector current depending on an illumination of the photosensitive element by light. The photodetector further comprises at least one evaluation unit for evaluating the detector current. The term “photosensitive element” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a single optically sensitive element or area. The photosensitive element may specifically comprise at least one single, uniform photosensitive area which is configured for receiving incident light which impinges on the individual photosensitive element and for generating an electrical signal depending on the intensity of the incident light, wherein the electrical signal may, in particular, be provided to the evaluation unit. The photosensitive element may comprise at least one substrate, specifically an electrically insulating substrate. For example, the photosensitive element may be a substrate having applied thereon or therein the at least one photosensitive area, which generates a physical response to the illumination for a given wavelength range. The photosensitive element may be configured for generating photoelectric charges upon illumination of a light-sensitive region by light. The generation of photoelectric charges by the photosensitive element over a certain period of time may result in the generation of a photoelectric current if a voltage is applied to the photosensitive element. The photosensitive element, specifically the photosensitive area of the photosensitive element, may comprise at least one photoconductive material selected from the group consisting of: lead sulfide (PbS); lead selenide (PbSe); mercury cadmium telluride (HgCdTe); cadmium sulfide (CdS); cadmium selenide (CdSe); indium antimonide (InSb); indium arsenide (InAs); indium gallium arsenide (InGaAs); silicon (Si); Silicon Germanium (SiGe); extrinsic semiconductors; organic semiconductors. The photosensitive element may be at least one of a photoresistor and a photodiode. For example, the photosensitive element may be or comprise a photoconductor, in particular an inorganic photoconductor. Alternatively or additionally, the photosensitive element may be or may comprise a photodiode. As a further alternative, the photosensitive element may be or may comprise at least one of pyroelectric, bolometer or thermophile detector elements.

[0020] The photodetector may specifically comprise a plurality of photosensitive elements. Specifically, the photodetector may be or may comprise at least one detector array, the detector array specifically comprising an array of the plurality of photosensitive elements. For example, the photodetector may be selected from any known pixel sensor, in particular, from a pixelated organic camera element, preferably, a pixelated organic camera chip, or from a pixelated inorganic camera element, preferably, a pixelated inorganic camera chip, more preferably from a CCD chip or a CMOS chip, which are, commonly, used in various cameras nowadays. The detector array may have a matrix of 1 x N pixels or of M x N pixels, wherein, as an example, M may be < 10 and N may be in the range from 1 to 50, preferably from 2 to 20, more preferred from 5 to 10. Additionally or alternatively, a monochrome camera element, preferably a monochrome camera chip, may be used, wherein the monochrome camera element may be differently selected for each optically sensitive element, especially, in accordance with the varying wavelength along the series of the optical sensors. Thus, the array may be adapted to provide a plurality of the electrical signals which may be generated by the photosensitive areas of the photosensitive elements comprised by the detector array. The electrical signals as provided by the detector array may be forwarded to the evaluation unit. The photosensitive element, in particular the array of photosensitive elements, may be designed to generate detector signals, preferably electronic signals, associated with the intensity of the incident light which impinges on the individual photosensitive elements. The detector signal may be an analogue and / or a digital signal. The electronic signals for adjacent pixelated sensors can, accordingly, be generated simultaneously or else in a temporally successive manner. By way of example, during a row scan or line scan, it is possible to generate a sequence of electronic signals which correspond to the series of the individual photosensitive elements which are arranged in a line. In addition, the individual photosensitive elements may, preferably, be active pixel sensors which may be adapted to amplify the electronic signals prior to providing it to the evaluation unit. For this purpose, the photodetector may comprise one or more signal processing devices, such as one or more filters and / or analogue-digital-converters for processing and / or preprocessing the electronic signals.

[0021] The term “detector current” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an electric current generated by the photodetector. An intensity of the detector current may specifically dependent on an illumination of the photosensitive element, specifically of a photosensitive area of the photosensitive element, by light. As outlined above, the photosensitive element may be configured for generating a photoelectric current upon illumination by light. The detector current may comprise the photoelectric current. However, the detector current may have further current sources. For example, the detector current may comprise, additionally or alternatively, a dark detector current, specifically a dark detector current being generated by the photodetector when no illumination impinges on the photosensitive element. The detector current may be or may comprise a current through the photosensitive element. The detector current may comprise the photocurrent generated by the photosensitive element in response to an illumination by light and a dark current.

[0022] The term “illumination” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an amount or an intensity of light impinging a certain area, specifically a photosensitive area of the photosensitive element. As used herein, the term “light” may refer, without limitation, to electromagnetic radiation in one or more of the infrared spectral range, the visible spectral range and the ultraviolet spectral range. Herein, the term “ultraviolet spectral range”, generally, refers to electromagnetic radiation having a wavelength of 1 nm to 380 nm, preferably of 100 nm to 380 nm. Further, in partial accordance with standard ISO-21348 in a valid version at the date of this document, the term “visible spectral range”, generally, refers to a spectral range of 380 nm to 760 nm. The term “infrared spectral range” (IR) generally refers to electromagnetic radiation of 760 nm to 1000 pm, wherein the range of 760 nm to 1.5 pm is usually denominated as “near infrared spectral range” (NIR) while the range from 1 .5 p to 15 pm is denoted as “mid infrared spectral range” (MidlR) and the range from 15 pm to 1000 pm as “far infrared spectral range” (FIR). Preferably, light used for the typical purposes of the present invention is light in the infrared (IR) spectral range, more preferred, in the near infrared (NIR) and / or the mid infrared spectral range (MidlR), especially the light having a wavelength of 1 pm to 5 pm, preferably of 1 pm to 3 pm. This is due to the fact that many material properties or properties on the chemical constitution of many objects may be derived from the near infrared spectral range. It shall be noted, however, that spectroscopy in other spectral ranges is also feasible and within the scope of the present invention.

[0023] The term “evaluation unit” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an arbitrary device or a combination of devices configured for evaluating, i.e. for processing at least one first item of information in order to generate at least one second item of information thereof. Thus, specifically, the evaluation unit may be configured for processing at least one input and to generate at least one output thereof. The evaluation unit may be or may comprise one or more integrated circuits, such as one or more application-specific integrated circuits (ASICs), and / or one or more data processing devices, such as one or more computers, digital signal processors (DSP) and / or field programmable gate array (FPGA), preferably one or more microcomputers and / or microcontrollers. For example, the evaluation unit may comprise at least one at least one printed circuit and / or at least one integrated circuit for evaluating the detector current and the reference current, such as at least one printed circuit and / or at least one integrated circuit having at least one measurement channel for each of the photosensitive element and the reference resistor. The evaluation unit may be configured for digitalizing the evaluated currents. Further, the evaluation unit may comprise digital signal processors (DSP) and / or field programmable gate array (FPGA) for further evaluating of the digitalized currents. Additional components may be comprised, such as one or more preprocessing devices and / or data acquisition devices, such as one or more devices for receiving and / or preprocessing of the currents, such as one or more AD-converters and / or one or more filters. Further, the evaluation unit may comprise one or more data storage devices. Further, the evaluation unit may comprise one or more interfaces, such as one or more wireless interfaces and / or one or more wire-bound interfaces.

[0024] The evaluation unit may be adapted to execute at least one computer program, such as at least one computer program performing and / or supporting the method according to the present invention, such as according to any one of the embodiments disclosed herein. As an example, one or more algorithms may be implemented which, by using the at least one detector current and the reference current as input variables, may perform a predetermined transformation for deriving the temperature-corrected detector impedance and the temperature-corrected reference impedance, respectively, and, further for deriving information on the degradation of the photodetector thereof. For this purpose, the evaluation unit may, particularly, comprise at least one data processing device, also referred to as a processor, in particular an electronic data processing device, which can be designed to generate the desired information by evaluating the detector current and the reference current. The evaluation unit may use an arbitrary process for generating the required information, such as by calculation and / or using at least one stored and / or known relationship. The evaluation unit specifically may be configured for performing at least one digital signal processing (DSP) technique using the detector current, the reference current and / or any secondary signal derived thereof.

[0025] The method comprises the following steps that may be performed in the given order. However, a different order may also be possible. In particular, one, more than one or even all of the method steps may be performed once or repeatedly. Further, the method steps may be performed successively or, alternatively, one or more of the method steps may be performed in a timely overlapping fashion or even in a parallel fashion and / or in a combined fashion. For example, step a) may be performed at least partially simultaneously to step b). The method may further comprise additional method steps that are not listed.

[0026] The method comprises: a) determining at least one detector current; b) evaluating the detector current with respect to at least one reference value to obtain at least one relative detector current value; and c) deriving at least one item of degradation information on the photosensitive element using the relative detector current value, the item of degradation information describing the degradation of performance due to temperature hysteresis behavior, aging, excessive temperatures and / or excessive illumination.

[0027] The term “determining” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a process of qualitatively or quantitatively measuring at least one variable or parameter, specifically at least one physical variable or parameter. The determining of the detector current may specifically comprise reading out the photodetector, specifically the photosensitive element, for accumulated photoelectric charges. Specifically, the determining of the detector current may comprise determining an analog detector current, e.g. by using one or more readout circuits comprised by the evaluation unit of the photodetector, such as one or more readout integrated circuits (ROIC). Additionally or alternatively, the determining of the detector current may comprise determining a digital detector current. Specifically, the determining of the detector current may comprise an analog-to-digital conversion of the detector current, e.g. by using an analog-to-digital converter, specifically for obtaining the detector current in a digital form for further processing by the evaluation unit.

[0028] The term “reference value” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a predefined or predetermined quantity used for comparison with another quantity. The reference value may specifically comprise a standard value, such as a standard value being defined or determined under standard or normal conditions. The reference value may comprise a numerical quantity being defined or determined by calculation or measurement. The reference value may be defined or determined prior to the method. The reference value may be kept constant during the method and / or during usage of the photodetector. The reference value may specifically be used for comparing the detector current to a predefined or predetermined standard value.

[0029] The term “evaluating the detector current with respect to at least one reference value” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a process of comparing at least one first quantity with at least one second quantity. The evaluating of the detector current with the reference value may comprise comparing the detector value with the reference value. The comparing may specifically comprise at least one operation using the detector current and the reference value, such as a mathematical operation comprising one or more algebraic operations. For example, the evaluating of the detector current with respect to the reference value may comprise determining a quotient or a ratio using the detector current and the reference value. As a result of the evaluating of the detector current, the relative detector current value may be obtained. As used herein, the term “relative detector current value” is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a detector current value being compared to at least one reference value. The relative detector current value may specifically comprise the result of the at least one operation using the detector current and the reference value. For example, the relative detector current value may comprise the quotient or ratio of the detector current and the reference value. However, other examples of operations and / or relative detector current values are also feasible.

[0030] The term “deriving” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to at least one action of processing at least one first item of information in order to generate at least one second item of information. The deriving of the item of degradation information may comprise processing the relative detector current value, such as in one or more processing steps, in order to generate the item of degradation information. Specifically, the deriving may comprise using at least one algorithm, such as at least one mathematical algorithm, for processing the relative detector current value to generate the item of degradation information. For example, the deriving of the item of degradation information may comprise using at least one relation between the relative detector current value and the item of degradation information. The relation may be used for associating the relative detector current value to the item of degradation information.

[0031] The term “item of degradation information” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to data conveying information on a degradation of a device. Specifically, the item of degradation information may comprise digital data, such as a number or sequence of numerical or alpha-numerical values, conveying information on a degradation of the photodetector, specifically of the pho- tosensitive element. The item of degradation information may comprise classification information on the degradation of the photodetector, specifically of the photosensitive element, e.g. a classification of the degradation being either “degraded” or “non-degraded”. Alternatively or additionally, the item of degradation information may comprise information on a degree of the degradation of the photodetector, specifically of the photosensitive element, e.g. a numerical value quantifying a degree of degradation. The item of degradation information may also comprise a combination of classification information and a degree of degradation, wherein, in case the degree of degradation exceeds a given or predetermined threshold, the photodetector, specifically the photosensitive element, is classified as "degraded”, wherein, in case the degree of degradation is equal to or below the given or predetermined threshold, the photodetector, specifically the photosensitive element, is classified as “non-degraded”. Further options are also feasible.

[0032] The item of degradation information may comprise at least one item of information selected from the group consisting of: at least one item of aging information, specifically comprising information on an aging of the photosensitive element; at least one item of hysteresis information, specifically comprising information on a hysteresis of the photosensitive element, more specifically information on a temperature hysteresis of the photosensitive element; at least one item of excessive temperature information; at least one item of excessive illumination information, specifically comprising information on at least one excessive illumination of the photosensitive element in at least one of the visible spectral range, the infrared spectral range and the ultraviolet spectral range.

[0033] As outlined above, the item of degradation information describes the degradation of performance due to temperature hysteresis behavior, aging, excessive temperatures and / or excessive illumination, specifically in at least one of a visible spectral range, an infrared spectral range and an ultraviolet spectral range.

[0034] The term “performance” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an ability of a device of performing at least one functionality. The performance of the photodetector, specifically of the photosensitive element, may refer to an ability of detecting illumination of the photosensitive element by light. The performance of the photodetector, specifically of the photosensitive element, may comprise a sensitivity of the photosensitive element with respect to the illumination by light. The sensitivity of the photosensitive element may comprise an ability of the photosensitive element to generate an amount of photoelectric charges in response to the illumination by light. For example, the performance of the photodetector, specifically of the photosensitive element, may be considered degraded if a constant illumination of the photosensitive element by light causes different detector currents, specifically lower detector currents. Vice versa, the performance of the photodetector, specifically of the photosensitive element, may be considered non-degraded if a constant illumination of the photosensitive element by light causes equal detector currents, at least within a detection error of the detector current. The performance of the photodetector, specifically of the photosensitive element, may depend on internal and / or external influences, such as temperature, aging, illumination or the like.

[0035] The term “temperature hysteresis behavior” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a dependence of a state or property of a device or element on a past evolution of at least one parameter influencing the state or property of the device or element. The performance of the photodetector, specifically of the photosensitive element, may depend on the temperature of the photodetector, specifically of the photosensitive element. For example, a temperature increase of the photodetector, specifically of the photosensitive element, from an initial temperature value may lead to an increase of the detector current, specifically assuming constant illumination by light. The increase of the detector current may remain a certain time after the temperature returns to the initial temperature value. Thus, the photodetector, specifically the photosensitive element, may be subject to temperature hysteresis behavior.

[0036] The term “aging” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a change of a state or property of a device or element over time. The aging of the photodetector, specifically of the photosensitive element, may comprise a change in the performance of the photodetector, specifically of the photosensitive element, over time, specifically irrespective of external influences on the performance. The aging may specifically comprise a decrease in the performance of the photodetector, specifically of the photosensitive element, compared to an initial state of the photodetector, specifically of the photosensitive element.

[0037] The term “excessive” as used herein, specifically in the context of “excessive temperature” or “excessive illumination”, is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an amount of a quantity or parameter exceeding a threshold of detrimental effects. Specifically, an excessive quantity or parameter may be present in an amount in which detrimental effects of the quantity or parameter can be expected. For example, the excessive temperatures may comprise any temperature above a given or predetermined threshold for which detrimental effects of the performance of the photodetector, specifically of the photosensitive element, can be expected, more specifically irreversible detrimental effects. For example, the excessive illumination may comprise any amount of illumination, specifically any amount of illumination in at least one of the visible spectral range, the infrared spectral range and the ultraviolet spectral range, above a given or predetermined threshold for which detrimental effects of the performance of the photodetector, specifically of the photosensitive element, can be expected, more specifically irreversible detrimental effects.

[0038] The detector current may comprise a dark detector current, specifically a dark detector current without illumination of the photosensitive element by light. The reference value may comprise at least one calibration value, specifically at least one predetermined calibration value. The calibration value may be predefined or predetermined and, specifically, may be kept constant during the method and / or usage of the photodetector. The relative detector current value may comprise at least one degradation quotient using the dark detector current and the calibration value. Step b) may optionally comprise a temperature correction of the dark detector current. The temperature-corrected dark detector current may be evaluated with respect to the calibration value. Thus, in this example, the relative detector current value may comprise a degradation quotient using the temperature-corrected dark detector current and the calibration value.

[0039] Alternatively or additionally, the photodetector may further comprise at least one reference resistor. The term “reference resistor” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an electric device having a known or predetermined electrical resistance. The resistance may be given by a ratio of a voltage drop at the reference resistor and the flow of electric current flowing through the reference resistor. The resistance of the reference resistor may depend on one or more external or internal quantities. For example, the resistance may depend on a temperature of the reference resistor. The reference resistor may have an essentially identical temperature dependency to the photosensitive element. The resistance of the reference resistor may be known or predetermined at least for one standard temperature. Alternatively or additionally, a temperature dependence of the resistance of the reference resistor may be known or predetermined, e.g. by using a temperature curve or a look-up table. As will be outlined in further detail below, the evaluation unit may comprise at least one printed circuit and / or at least one integrated circuit. The reference resistor may be part of the printed circuit or the integrated circuit, respectively.

[0040] The photodetector may be configured for generating at least one reference current through the reference resistor. The term “reference current” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an electric current through the reference resistor. The reference current may be generated by applying voltage, e.g. a bias voltage, to the reference resistor.

[0041] The evaluation unit may be configured for evaluating the reference current. Specifically, step a) may comprise determining a dark detector current and the reference current through the reference resistor. Further, in step b), the reference current may be used as the reference value. The relative detector current value may comprise at least one degradation quotient using the dark detector current and the reference current. Step b) may optionally comprise a temperature correction of the dark detector current and the reference current. The temperature-corrected dark detector current may be evaluated with respect to the temperature-corrected reference current. Thus, in this example, the relative detector current value may comprise a degradation quotient using the temperature-corrected dark detector current and the temperature-corrected reference current. Alternatively or additionally, as an option, step a) may further comprise determining at least one temperature-corrected detector impedance of the photosensitive element from the detector current. Step a) may further comprise determining at least one temperature-corrected reference impedance of the reference resistor from the reference current. In step b), the temperature-corrected reference impedance may be used as the reference value. The temperature-corrected detector impedance may be evaluated with respect to the temperature-corrected reference impedance. The relative detector current value may comprise at least one degradation quotient using the temperature-corrected detector impedance and the temperature-corrected reference impedance.

[0042] For example, the photodetector may further comprise at least one skimming circuit for skimming the detector current separating a measurement current to the evaluation unit and a skimming current to the skimming circuit. The detector current may be a sum of the measurement current and the skimming current. The reference resistor may be used to determine the skimming current by comparing the detector current and the reference current. A known or predetermined bias voltage may be applied to the photosensitive element, wherein the temperature-corrected detector impedance may be determined using the bias voltage, the measurement current and the skimming current. For example, an absolute value of the bias voltage applied to a photodiode may be in the range of 0 V to 10 V, specifically in the range of 0 V to 8 V, more specifically in the range of 0.5 V to 2 V. As an example, the photodiode may be operated with zero bias voltage. Alternatively, the photodiode may be operated with a reverse bias voltage, i.e. a negative bias voltage having an absolute value in the range of 0 V to 10 V, specifically in the range of 0 V to 8 V, more specifically in the range of 0.5 V to 2 V. The bias voltage applied to a photoresistor may be dependent on the resistance of the photoresistor. The bias voltage applied to a photoresistor may be in the range of 0 V to 50 V, specifically in the range of 1 V to 20 V, more specifically in the range of 1 V to 10 V. Alternatively, an alternating bias voltage may be applied to the photoresistor, specifically having an amplitude in the range of 0 V to 50 V, specifically in the range of 1 V to 20 V, more specifically in the range of 1 V to 10 V. The known or predetermined bias voltage may be applied to the reference resistor, wherein the temperature-corrected reference impedance may be determined using the bias voltage and the reference current. In this example, the determining of the temperature-corrected detector impedance of the photosensitive element and the determining of the temperature-corrected reference impedance of the reference resistor may be performed at least partially simultaneously. The temperature-corrected reference impedance may be determined using the same or an equivalent circuit used for determining the temperature-corrected detector impedance.

[0043] The photodetector may comprise a plurality of photosensitive elements. The determining of the temperature-corrected detector impedance and the deriving of the item of degradation information may be performed for each photosensitive element of the plurality of photosensitive elements. The temperature-corrected reference impedance may be determined once for all of the plurality of photosensitive elements. However, it may also be possible to have a plurality of ref- erence resistors, each reference resistor being associated with at least one photosensitive element of the plurality of photosensitive elements, and, thus, to determine the temperature-corrected reference impedance for each reference resistor of the plurality of reference resistors.

[0044] The term “impedance” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to at least one measure indicating an opposition of an object to a flow of electric current, specifically to alternating electric current. The impedance of an object may specifically comprise the object's resistance and reactance. The impedance of an object may be quantified by a ratio of a voltage drop at the object and the flow of electric current flowing through the object. Consequently, the term “detector impedance” as used herein may refer, without limitation, to an impedance of the photodetector, specifically of the photosensitive element. Similarly, the term “reference impedance” as used herein may refer, without limitation, to an impedance of the reference resistor.

[0045] The term “temperature-corrected” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a property of a quantity or measure of having considered temperature effect in the process of determining the quantity or measure. Specifically, temperature effects on the quantity or measure, e.g. a change in the quantity or measure due to temperature change, may be considered when a temperature- corrected quantity or measure is determined. The temperature-corrected quantity or measure may comprise the quantity or measure adjusted for temperature effects. For example, the temperature-corrected impedance may comprise an impedance being corrected for any temperature-induced changed of the impedance. The temperature-corrected impedance may be determined with respect to a reference temperature, e.g. a standard temperature under standard conditions, such as normal temperature.

[0046] The temperature-corrected detector impedance may be determined using the bias voltage, the measurement current and the skimming current. Similarly, a known or predetermined bias voltage may be applied to the reference resistor. The temperature-corrected reference impedance may be determined using the bias voltage and the reference current. The evaluation unit, specifically the printed or integrated circuit of the evaluation unit, may be configured, e.g. by using one or more electronic or digital switches, for receiving the detector current from the photosensitive element or, alternatively, from the reference resistor, e.g. via different measurement channels of the evaluation unit. Alternatively, however, the evaluation unit may also be configured for receiving the detector current from both the photosensitive element and the reference resistor, e.g. simultaneously via different measurement channels of the evaluation unit.

[0047] The temperature-corrected reference impedance in step b) may be determined using the same or equivalent circuit used for determining the temperature-corrected detector impedance. Thus, the evaluation unit may be configured for evaluating both the detector current from the photosensitive element and the reference current from the reference resistor. Alternatively or additionally, the photodetector may be comprised by at least one spectrometer device, specifically by at least one spectrometer device according to any one of the embodiments of a spectrometer device described in further detail below. Specifically, the photodetector may be part of the spectrometer device. The spectrometer device may comprise at least one light source for generating illumination light illuminating an object applied to at least one object interface of the spectrometer device. The illumination light may specifically comprise light in at least one optical spectral range, as will be outlined in further detail below. The spectrometer device may further comprise at least one first optical path configured for allowing the illumination light to propagate to the photodetector by passing the object interface at least once. The spectrometer device may further comprise at least one second optical path configured for allowing the illumination light to propagate to the photodetector without passing the object interface. The method may comprise in step a) determining at least one dark detector current and at least one illumination detector current via the second optical path. Further, in step b), the illumination detector current may be evaluated with respect to the dark detector current.

[0048] The dark detector current may specifically be determined having no illumination light on the photodetector via the second optical path. The illumination detector current may specifically be determined with illumination of the photodetector by the light source via the second optical path. The illumination detector current may be determined at a predefined or predetermined illumination power of the light source.

[0049] Further, optionally, step b) may comprise a temperature correction of the dark detector current and the illumination detector current. The temperature-corrected illumination detector current may be evaluated with respect to the temperature-corrected dark detector current.

[0050] The relative detector current value may comprise at least one degradation quotient using the illumination detector current, specifically the temperature-corrected illumination detector current, and the dark detector current, specifically the temperature-corrected dark detector current.

[0051] As used herein, the term “degradation quotient” is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a fraction of at least two numbers, values or quantities comprising information on the degradation. Specifically, the degradation quotient may be or may comprise a quotient of the detector current and the reference value. The item of degradation information on the photosensitive element may specifically be derived using the degradation quotient, specifically directly from the degradation quotient and / or indirectly, such as by performing one or more processing steps with the degradation quotient. For example, the item of degradation information may indicate a degraded photosensitive element if the degradation quotient differs from a predetermined value by more than a given threshold, specifically by more than 20 % of the predetermined value, more specifically by more than 10 % of the predetermined value. The predetermined value may be defined or determined by determining the detector current of a pristine photodetector, such as a newly manufactured photodetector, and evaluating the pristine detector current with respect to the reference value.

[0052] Further, as outlined above, the photodetector may comprise a plurality of photosensitive elements. The method may performed for each photosensitive element. For example, the method may be performed for each photosensitive element individually, such as for each photosensitive element independently from the other photosensitive elements. Alternatively or additionally, the deriving of the item of degradation information on the photosensitive element may comprise comparing the degradation quotients of the plurality of photosensitive elements. The item of degradation information may indicate a degraded photosensitive element if a degradation quotient for the photosensitive element differs from at least one comparison degradation quotient of the plurality of photosensitive elements by more than a given threshold. The comparison degradation quotient of the plurality of photosensitive elements may comprise at least one of: a mean of the degradation quotients of the plurality of photosensitive elements, specifically an arithmetic mean of the degradation quotients of the plurality of photosensitive elements; a minimum degradation quotient of the degradation quotients of the plurality of photosensitive elements; a maximum degradation quotient of the degradation quotients of the plurality of photosensitive elements. For example, the degradation quotient of one the photosensitive elements may be compared to an arithmetic mean of the degradation quotients of the plurality of photosensitive elements to derive the item of degradation information on the photosensitive element. The comparing may specifically be performed in case the photodetector may comprise a number of photosensitive elements for which the arithmetic mean of the degradation quotient may not be influenced by one degraded photosensitive element, e.g. for a number of 16 photosensitive elements or more. Alternatively or additionally, as another example, the degradation quotient of one photosensitive element may be compared to one or both of a maximum degradation quotient and a minimum degradation quotient of the degradation quotients of the plurality of photosensitive elements to derive the item of degradation information on the photosensitive element, specifically in case the number of photosensitive elements may be less than 16.

[0053] The method may further comprise identifying a defective photosensitive element if the degradation quotient exceeds a number of 10, specifically a number of 5, more specifically a number of 2. For example, in case of a reference resistor, the resistance of the reference resistor may be chosen to be equal to a resistance of the photosensitive element at a standard or reference temperature, specifically at least within an error range of the respective resistance values. As outlined above, the bias voltage may be applied to both the photosensitive element and the reference resistor to determine the detector current and the reference current, respectively. The degradation quotient using the dark detector current and the reference current may be equal to unity at the standard or reference temperature, specifically for non-degraded photosensitive elements. Alternatively or additionally, the calibration value may be determined in accordance with a dark current value of the photodetector in a pristine state of the photodetector at a standard or reference temperature. The degradation quotient using the dark detector current and the calibration value may be equal to unity at the standard or reference temperature, specifically for non-degraded photosensitive elements. Alternatively or additionally, in general, it may be possible to determine the degradation quotient such that the degradation quotient is equal to unity for a non-degraded photosensitive element, e.g. by using one or more normalization factors. In any case, if the degradation quotient differs by more than a given threshold, e.g. by more than 20 %, from unity, a degraded photodetector, specifically a degraded photosensitive element, may be determined. In case the degradation quotient exceeds a factor of 2, the photodetector, specifically the photosensitive element may be determined defective. Thus, it may be important to monitor the degradation quotient for the photodetector, specifically for the photosensitive element, in order to avoid having the photodetector, specifically the photosensitive element, in a defective state.

[0054] The method may comprise, if the item of degradation information indicates a degraded photosensitive element, preventing displaying an erroneous measurement performed with the degraded photosensitive element.

[0055] Alternatively or additionally, the method may comprise, if the item of degradation information indicates a degraded photosensitive element for a predetermined period of time, identifying a defective photosensitive element.

[0056] The photodetector may further comprise at least one temperature sensor for determining at least one temperature, specifically at least one temperature of the photosensitive element. The method may further comprise, specifically prior to step a) or at least partially simultaneously, determining at least one temperature, specifically at least one temperature of the photosensitive element. The temperature may be used to determine a temperature correction, specifically a temperature correction for one or more of the detector current and the reference current, more specifically a temperature correction comprising temperature compensation curves. For example, the detector current may be temperature-corrected by using temperature compensation curves, such as a temperature compensation curve comprising temperature compensation coefficients for at least one temperature range, the temperature compensation coefficients compensating temperature-induced changes of the detector current with respect to a standard or reference temperature. Alternatively or additionally, the reference current may be temperature-corrected by using temperature compensation curves, such as a temperature compensation curve comprising temperature compensation coefficients for at least one temperature range, the temperature compensation coefficients compensating temperature-induced changes of the reference current with respect to a standard or reference temperature.

[0057] The photodetector may further comprise at least one skimming circuit for skimming the detector current separating a measurement current to the evaluation unit and a skimming current to the skimming circuit. The skimming circuit may be an arbitrary electric circuit configured for skimming the detector current. Step a) may specifically comprise determining both the measurement current and the skimming current. The detector current may be a sum of the measurement current and the skimming current. As an example, the reference resistor may be used to determine the skimming current by comparing the detector current and the reference current. The reference resistor may be used to get more accurate relation between detector signal and current by calibrating the detector current and the skimming current.

[0058] As outlined above, a known or predetermined bias voltage may be applied to the photosensitive element. For example, an absolute value of the bias voltage applied to a photodiode may be in the range of 0 V to 10 V, specifically in the range of 0 V to 8 V, more specifically in the range of 0.5 V to 2 V. As an example, the photodiode may be operated with zero bias voltage. Alternatively, the photodiode may be operated with a reverse bias voltage, i.e. a negative bias voltage having an absolute value in the range of 0 V to 10 V, specifically in the range of 0 V to 8 V, more specifically in the range of 0.5 V to 2 V. The bias voltage applied to a photoresistor may be dependent on the resistance of the photoresistor. The bias voltage applied to a photoresistor may be in the range of 0 V to 50 V, specifically in the range of 1 V to 20 V, more specifically in the range of 1 V to 10 V. Alternatively, an alternating bias voltage may be applied to the photoresistor, specifically having an amplitude in the range of 0 V to 50 V, specifically in the range of 1 V to 20 V, more specifically in the range of 1 V to 10 V.

[0059] The method, specifically step b) and / or step c), may be at least partially computer-implemented. Further details regarding the computer-implementation will be outlined in further detail below.

[0060] In a further aspect of the present invention, a photodetector is disclosed, comprising at least one photosensitive element, the photodetector being configured for generating at least one detector current depending on an illumination of the photosensitive element by light, wherein the photodetector further comprises at least one evaluation unit for evaluating the detector current. For definitions of terms and possible embodiments of the photodetector or any part thereof, reference is made to the description of the method for evaluating degradation of a photodetector.

[0061] The photodetector may comprise at least one reference resistor. The photodetector may be configured for generating at least one reference current. The evaluation unit may be configured for evaluating the reference current.

[0062] The photodetector is configured for performing the method according to the present invention, such as according to any one of the embodiments disclosed above and / or according to any one of the embodiments disclosed in further detail below.

[0063] In a further aspect of the present invention, a spectrometer device, specifically a portable spectrometer device, for obtaining spectroscopic information on at least one object is disclosed, the spectrometer device comprising at least one photodetector according to the present invention, such as according to any one of the embodiments disclosed above and / or according to any one of the embodiments disclosed in further detail below. The term “spectrometer device” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an optical device configured for acquiring at least one item of spectral information on at least one object. Specifically, the at least one item of spectral information may refer to at least one optical property or optically measurable property which is determined as a function of a wavelength, for one or more different wavelengths. More specifically, the optical property or optically measurable property, as well as the at least one item of spectral information, may relate to at least one property characterizing at least one of a transmission, an absorption, a reflection and an emission of the at least one object, either by itself or after illumination with external light. The at least one optical property may be determined for one or more wavelengths. The spectrometer device specifically may form an apparatus which is capable of recording a signal intensity with respect to the corresponding wavelength of a spectrum or a partition thereof, such as a wavelength interval, wherein the signal intensity may, specifically, be provided as an electrical signal which may be used for further evaluation.

[0064] The spectrometer device, as an example, may be or may comprise a device which allows for a measurement of at least one spectrum, e.g. for the measurement of a spectral flux, specifically as a function of a wavelength or detection wavelength. The spectrum may be acquired, as an example, in absolute units or in relative units, e.g. in relation to at least one reference measurement. Thus, as an example, the acquisition of the at least one spectrum specifically may be performed either for a measurement of the spectral flux (unit W / nm) or for a measurement of a spectrum relative to at least one reference material (unit 1 ), which may describe the property of a material, e.g., reflectance over wavelength. Additionally or alternatively, the reference measurement may be based on a reference light source, an optical reference path, a calculated reference signal, e.g. a calculated reference signal from literature, and / or on a reference device.

[0065] Specifically, the at least one spectrometer device may be a diffusive reflective spectrometer device configured for acquiring spectral information from the light which is diffusively reflected by the at least one object, e.g. the at least one sample. Additionally or alternatively, the at least one spectrometer device may be or may comprise an absorption- and / or transmission spectrometer. In particular, measuring a spectrum with the spectrometer device may comprise measuring absorption in a transmission configuration. Specifically, the spectrometer device may be configured for measuring absorption in a transmission configuration. As outlined above, however, other types of spectrometer devices are also feasible.

[0066] The spectrometer device, as will be outlined in further detail below, may comprise at least one light source, in particular at least one artificial light source. The light source, as an example, may be at least one of a tunable light source, a light source having at least one fixed emission wavelength and a broadband light source. Other embodiments of light source may be possible, too. For example, ambient light may be used. The spectrometer device further comprises the at least one photodetector, the photodetector specifically being configured for detecting light, such as light which is at least one of transmitted, reflected or emitted from the at least one object. The spectrometer device further may comprise, as will be outlined in further detail below, at least one wavelength-selective element, such as at least one of a grating, a prism and a filter, e.g. a length variable filter having varying transmission properties over its lateral extension. The wavelength-selective element may be used for separating incident light into a spectrum of constituent wavelength signals whose respective intensities are determined by employing the photodetector, such as the photodetector having an array of photosensitive elements as described above.

[0067] The spectrometer device, specifically, may be a portable spectrometer device. The term “portable” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to the property of at least one object of being moved by human force, such as by a single user. Specifically, the object characterized by the term “portable” may have a weight not exceeding 10 kg, specifically not exceeding 5 kg, more specifically not exceeding 1 kg or even not exceeding 500 g. Additionally or alternatively, the dimensions of the object characterized by the term “portable” may be such that the object extends by no more than 0.3 m into any dimension, specifically by no more than 0.2 m into any dimension. The object, specifically, may have a volume of no more than 0.03 m3, specifically of no more than 0.01 m3, more specifically no more than 0.001 m3or even no more than 500 mm3. In particular, as an example, the portable spectrometer device may have dimensions of e.g. 10 mm by 10 mm by 5 mm. Specifically, the portable spectrometer device may be part of a mobile device or may be attachable to a mobile device, such as a notebook computer, a tablet, a cell phone, such as a smartphone, a smartwatch and / or a wearable computer, also referred to as “wearable”, e.g. a body borne computer such as a wrist band or a watch. In particular, the weight of the spectrometer device, specifically the portable spectrometer device, may be in the range from 1 g to 100 g, more specifically in the range from 1 g to 10 g.

[0068] The term “spectroscopic information”, also referred to as “spectral information” or as “an item of spectral information”, as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an item of information, e.g. on at least one object and / or radiation emitted by at least one object, characterizing at least one optical property of the object, more specifically at least one item of information characterizing, e.g. qualifying and / or quantifying, at least one of a transmission, an absorption, a reflection and an emission of the at least one object. As an example, the at least one item of spectral in formation may comprise at least one intensity information, e.g. information on an intensity of light being at least one of transmitted, absorbed, reflected or emitted by the object, e.g. as a function of a wavelength or wavelength sub-range over one or more wavelengths, e.g. over a range of wavelengths. Specifically, the intensity information may correspond to or be derived from the signal intensity, specifically the electrical signal, recorded by the spectrometer device with respect to a wavelength or a range of wavelengths of the spectrum. The spectrometer device specifically may be configured for obtaining at least one spectrum or at least a part of a spectrum of detection light propagating from the object to the spectrometer device. The spectrum may describe the radiometric unit of spectral flux, e.g. given in units of watt per nanometer (W / nm), or other units, e.g. as a function of the wavelength of the detection light. Thus, the spectrum may describe the optical power of light, e.g. in the NIR spectral range, in a specific wavelength band. The spectrum may contain one or more optical variables as a function of the wavelength, e.g. the power spectral density, electric signals derived by optical measurements and the like. The spectrum may indicate, as an example, the power spectral density and / or the spectral flux of the object, e.g. of a sample, e.g. relative to a reference sample, such as a transmittance and / or a reflectance of the object. The spectrometer device may be configured for obtaining the spectrum in wavelength range at least partially comprising one or more of an infrared, a visible and an ultraviolet spectral range. The spectrometer device may be a near-infrared spectrometer. For example, the spectrometer device may be configured for obtaining the spectrum in a wavelength range at least partially comprising the near-infrared spectral range, such as in a wavelength range from 760 nm to 5 pm, specifically in a wavelength range from 1 pm to 3 pm.

[0069] The spectrum, as an example, may comprise at least one measurable optical variable or property of the detection light and / or of the object, specifically as a function of the illumination light and / or the detection light. As an example, the at least one measurable optical variable or property may comprise at least one at least one radiometric quantity, such as at least one of a spectral density, a power spectral density, a spectral flux, a radiant flux, a radiant intensity, a spectral radiant intensity, an irradiance, a spectral irradiance. Specifically, as an example, the spectrometer device, specifically the detector, may measure the irradiance in Watt per square meter (W / m2), more specifically the spectral irradiance in Watt per square meter per nanometer (W / m2 / nm). Based on the measured quantity the spectral flux in Watt per nanometer (W / nm) and / or the radiant flux in Watt (W) may be determined, e.g. calculated, by taking into account an area of the photodetector.

[0070] The term “object” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an arbitrary body, chosen from a living object and a non-living object. Thus, as an example, the at least one object may comprise one or more articles and / or one or more parts of an article, wherein the at least one article or the at least one part thereof may comprise at least one component which may provide a spectrum suitable for investigations. Additionally or alternatively, the object may be or may comprise one or more living beings and / or one or more parts thereof, such as one or more body parts of a human being, e.g. a user, and / or an animal. The object specifically may comprise at least one sample which may fully or partially be analyzed by spectroscopic methods. As an example, the object may be or may comprise at least one of: human or animal skin; edibles, such as fruits; plastics and textile. The spectrometer device may further comprise at least one light source for generating illumination light illuminating the object applied to at least one object interface of the spectrometer device. The term “light source” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an arbitrary device configured for generating or providing light. The light source specifically may be or may comprise at least one electrical light source, such as an electrically driven light source.

[0071] The light source may be configured for emitting light in a spectral range at least partially comprising the infrared spectral range, specifically the near-infrared spectral range, more specifically in a spectral range from 300 nm to 3 pm, more specifically in a spectral range from 760 nm to 3 pm, more specifically in a spectral range from 1 pm to 20 pm, more specifically in a spectral range from 1 pm to 2.5 pm, more specifically in a spectral range from 1 .3 pm to 2.5 pm, most specifically in a spectral range from 1 .5 pm to 2.2 pm.

[0072] For example, the light source may comprise at least one light source selected from the group consisting of: an incandescent lamp; a light emitting diode (LED); a laser, a laser diode, a solid- state laser, a gas laser, a quantum cascade laser, a plasma light source. For example, the light source may comprise a blue light LED having a primary light emission at 440 nm and, optionally, further comprising at least one luminescent material for at least partially converting the primary light at least partially into light the infrared spectral range, specifically the near-infrared spectral range, e.g. a phosphor luminescent material.

[0073] The term “object interface” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a port of the spectrometer device through which light in the optical spectral range, such as in at least one partition of the optical spectral range or in the full optical spectral range, may enter the spectrometer device, specifically for the purpose of the spectral sensing, and / or may leave the spectrometer device, e.g. for the purpose of illuminating the at least one object. The object interface, as an example, may define an optical plane, e.g. a plane either material or imaginary, of the spectrometer device, through which the illumination light from a first optical path, as will be explained in further detail below, may travel to reach the object and / or through which the detection light from the object may travel to reach the photodetector, e.g. to generate a detector signal. The object interface may be a fictional plane The object interface may or may not be constituted by a physical element and / or barrier, such as a transparent element, e.g. a glass or quartz window. The object interface may also be defined by a surface of the object itself or by a plane where the object can be placed or aligned. As an example, the object interface may be or may comprise at least one element comprising at least one transparent material being at least partially transparent in the optical spectral range, such as in at least one partition of the optical spectral range or in the full optical spectral range. The object interface may be configured for transmitting light in the optical spectral range. The object interface may be arranged in an optical path of the spectrometer device, specifically in the first optical path, to allow the illumination light emitted from the light source to illuminate the object placed in front of the spectrometer device, specifically in front of the object interface. The transparent material may, as an example, comprise one or more of a glass material, such as silica, soda lime, borosilicate or the like, and / or a polymeric material, such as polymethylmethacrylate or polystyrene.

[0074] The spectrometer device may further comprise at least one first optical path configured for allowing the illumination light to propagate to the photodetector by passing the object interface at least once. The spectrometer device may further comprising at least one second optical path configured for allowing the illumination light to propagate to the photodetector without passing the object interface.

[0075] The term “optical path” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to a trajectory of light in the spectrometer device. The optical path of light in the spectrometer device may be affected by reflection, refraction, dispersion and / or absorption at one or more optical elements, such as lenses, prisms, mirrors, gratings or the like, comprised by the spectrometer device. The terms “first” and “second”, as generally used herein, are used for nomenclature, only, without implying any ranking or numbering.

[0076] The term “first optical path” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an optical path with interaction of the illumination light at the object. Specifically, a detector signal obtained via the first optical path may be affected from a presence and / or an absence of the object at the spectrometer device, specifically at the object interface of the spectrometer device. For example, a detector signal obtained via the first optical path having the object applied to the spectrometer device may be different from a detector signal obtained via the first optical path having no object applied to the spectrometer device, specifically irrespective of constant environmental conditions. In particular, the first optical path may be configured for allowing the illumination light emitted from the light source to propagate to the photodetector, optionally via at least one wave- length-selective element, by passing the object interface at least once. Specifically, the first optical path may allow the illumination light emitted from the light source to propagate to the object interface and, subsequently, to the photodetector, optionally via at least one wavelength-selective element. Via the first optical path, the illumination light emitted from the light source may be guided directly or indirectly, such as by reflection, refraction and / or dispersion, to the object interface. The first optical path may be partially arranged outside the spectrometer device, such as outside a housing of the spectrometer device. Specifically, the illumination light in the first optical path may leave the spectrometer device, in particular a housing of the spectrometer device, at the object interface to illuminate the object arranged outside the spectrometer device. The first optical path may be configured for coupling the detection light reflected at the object back into the spectrometer device. The detection light may be guided from the object interface di- rectly or indirectly, such as by reflection, refraction and / or dispersion, to the photodetector, optionally via at least one wavelength-selective element. The reflection at the object may comprise a diffuse reflection. Specifically, the detection light in the first optical path illuminating the photodetector may be light diffusively reflected at the object. The photodetector may be configured for generating at least one detector signal in response to an illumination by incident light via the first optical path.

[0077] The term “passing the object interface” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to one or more of propagating to the object interface and from the object interface, traversing the object interface, and / or interacting with the object interface. The illumination light may impinge on the object interface, e.g. under an angle of incidence. The illumination light may interact with the object interface and may leave the object interface, e.g. under an exit angle. The illumination light may traverse the object interface and may illuminate the object received at the object interface.

[0078] The term “second optical path” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an optical path without interaction of the illumination light at the object. Specifically, a detector signal obtained via the second optical path may be unaffected from a presence and / or an absence of the object at the spectrometer device. For example, a detector signal obtained via the second optical path having the object applied to the spectrometer device, specifically to the object interface, may be equal to a detector signal obtained via the second optical path having no object applied to the spectrometer device, specifically assuming constant environmental conditions. In particular, the second optical path may be configured for allowing the illumination light emitted from the light source to propagate to the photodetector, optionally via at least one wavelength-selective element, without passing the object interface, specifically without being reflected at the object. The second optical path may be arranged completely in the spectrometer device, such as within a housing of the spectrometer device. The illumination light following the second optical path may be emitted by the light source and may be directly or indirectly, such as by reflection, refraction and / or dispersion, guided to the photodetector. For example, the second optical path may comprise at least one internal reflection target, wherein the illumination light emitted from the light source via the second optical path may be passed to the internal reflection target and subsequently to the photodetector without interacting with the object at the object interface. Alternatively or additionally, the second optical path may comprise a fiber coupled optical path transferring light from the light source to the photodetector. Alternatively or additionally, the second optical path may be configured for direct illumination of the photodetector with the illumination light emitted from the light source. The detector may be configured for generating at least one detector signal in response to an illumination by incident light via the second optical path.

[0079] As an example, the spectrometer device may comprise at least two light sources, wherein at least one light source is arranged in each of the first optical path and the second optical path. Alternatively, the spectrometer device may comprise at least one light source configured for emitting the illumination light into the first optical path and the second optical path.

[0080] The spectrometer device may comprise at least one wavelength-selective element for selectively transferring detection light from the object to the photodetector. The term “wavelength-selective element” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an optical device or element which interacts with differing spectral portions of incident light in a different manner, e.g. by having at least one wavelength-dependent optical property, such as at least one wavelength-dependent optical property selected from the list consisting of a degree of reflection, a direction of reflection, a degree of refraction, a direction of refraction, an absorption, a transmission, an index of refraction.

[0081] The wavelength-selective element specifically may be selected from the group of a tunable wavelength-selective element and a wavelength-selective element having a fixed transmission spectrum. By using a tunable wavelength-selective element, as an example, differing wavelength ranges may be selected sequentially, whereas, by using a wavelength-selective element having a fixed transmission spectrum, the selection of the wavelength ranges may be fixed and may, however, be dependent e.g. on a detection position, thereby allowing, as an example, for simultaneously exposing photodetectors and / or different photosensitive elements of the photodetector to differing spectral ranges of light.

[0082] The wavelength-selective element may comprise at least one of a filter, a grating, a prism, a plasmonic filter, a diffractive optical element and a metamaterial. The wavelength-selective element may comprise one or more of a dispersive (e.g. prism), or diffractive (grating) element, or a detector with an inherently limited bandwidth of its spectral response. Additionally or alternatively, the wavelength-selective element may comprise at least one of the following elements: an array of individual bandpass filters, an array of patterned filters, a MEMS-lnterferometer, a MEMS-Fabry Perot interferometer. Further elements are feasible.

[0083] In a further aspect of the present invention, a computer program is disclosed, comprising instructions which, when the program is executed by a photodetector according to the present invention, such as according to any one of the embodiments disclosed above and / or according to any one of the embodiments disclosed in further detail below, cause the photodetector to perform the method according to the present invention, such as according to any one of the embodiments disclosed above and / or according to any one of the embodiments disclosed in further detail below.

[0084] In a further aspect of the present invention, a computer-readable storage medium, specifically a non-transient computer-readable storage medium, is disclosed, comprising instructions which, when the instructions are executed by a photodetector according to the present invention, such as according to any one of the embodiments disclosed above and / or according to any one of the embodiments disclosed in further detail below, cause the photodetector to perform the method according to the present invention, such as according to any one of the embodiments disclosed above and / or according to any one of the embodiments disclosed in further detail below.

[0085] As used herein, the term “computer-readable storage medium” specifically may refer to non- transitory data storage means, such as a hardware storage medium having stored thereon computer-executable instructions. The computer-readable storage medium specifically may be or may comprise a storage medium such as a random-access memory (RAM) and / or a read-only memory (ROM). The computer-readable storage medium may be or may comprise at least one computer-readable data carrier.

[0086] Referring to the computer-implemented aspects of the invention, one or more of the method steps or even all of the method steps of the method according to one or more of the embodiments disclosed herein may be performed by using a computer or computer network. Thus, generally, any of the method steps including provision and / or manipulation of data may be performed by using a computer or computer network. Generally, these method steps may include any of the method steps, typically except for method steps requiring manual work, such as providing the samples and / or certain aspects of performing the actual measurements.

[0087] As used herein, the terms “have”, “comprise” or “include” or any arbitrary grammatical variations thereof are used in a non-exclusive way. Thus, these terms may both refer to a situation in which, besides the feature introduced by these terms, no further features are present in the entity described in this context and to a situation in which one or more further features are present. As an example, the expressions “A has B”, “A comprises B” and “A includes B” may both refer to a situation in which, besides B, no other element is present in A (i.e. a situation in which A solely and exclusively consists of B) and to a situation in which, besides B, one or more further elements are present in entity A, such as element C, elements C and D or even further elements.

[0088] Further, it shall be noted that the terms “at least one”, “one or more” or similar expressions indicating that a feature or element may be present once or more than once typically are used only once when introducing the respective feature or element. In most cases, when referring to the respective feature or element, the expressions “at least one” or “one or more” are not repeated, nonwithstanding the fact that the respective feature or element may be present once or more than once.

[0089] Further, as used herein, the terms "preferably", "more preferably", "particularly", "more particularly", "specifically", "more specifically" or similar terms are used in conjunction with optional features, without restricting alternative possibilities. Thus, features introduced by these terms are optional features and are not intended to restrict the scope of the claims in any way. The invention may, as the skilled person will recognize, be performed by using alternative features. Simi- larly, features introduced by "in an embodiment of the invention" or similar expressions are intended to be optional features, without any restriction regarding alternative embodiments of the invention, without any restrictions regarding the scope of the invention and without any restriction regarding the possibility of combining the features introduced in such way with other optional or non-optional features of the invention.

[0090] The method and the devices according to the present invention may provide a large number of advantages over known method and devices. Specifically, the method and the devices according to the present invention may ensure long-term usability of photodetectors, in particular for consumer spectroscopy systems. Additionally, bad or false measurements with degraded photodetectors can be avoided which specifically may avoid bad user experience. The method may specifically be performed using photodetectors without adding additionally required hardware components or requiring extra measurement time. The method may specifically be configured for evaluating degradation by exploiting information obtained from the required skimming during readout of the photodetector. Further, the method and devices according to the present invention may solve the problem arising from an uncontrollable environment, e.g. an environment being implemented as a part of a larger system, as then no dedicated measurements can be performed, that are not user triggered. Specifically, in large systems or large environments, e.g. in situations where the photodetector and / or the spectrometer device form part of a larger system, such as in a handheld multipurpose device or in a production machine, the photodetector may be subject to degradation or aging but is not used itself and maintenance or monitoring is not actively performed by the user. In this situation, the method and devices according to the present invention may provide the possibility to monitor the degradation or aging even when the photodetector is not actively used and may trigger maintenance to prevent use of a degraded or faulty device. Further, the method and devices according to the present invention may allow continuously monitoring degradation of photodetectors without any user interaction triggering the evaluation. The information on the detector current, the reference current and / or the respective impedances may be measured or determined from the obtained data in the background and, thus, may allow to derive the item of degradation information every time the photodetector or the spectrometer device is used. Additionally, data generated by the method on the long-term usage of the photodetector can be obtained for further developments or evaluation.

[0091] The method for evaluating degradation of a photodetector may specifically be performed before and / or during each measurement triggered by the user of the photodetector. A temperature of the photodetector, specifically of the photosensitive element, may be determined and may be logged to compensate the detector current based on the detector temperature. The detector impedance may be calculated from the bias voltage and the sum of skimming current and measurement current. The reference impedance of the reference resistor may be determined in order to prevent other temperature effects from affecting the measurement. The impedances may be compensated by temperature curves. The degradation quotient using a relation between the temperature-corrected reference impedance and the temperature-corrected detector impedance may be determined in order to derive the item of degradation information, such as an aging quo- tient, the item of degradation information specifically comprising information for detecting defective photodetectors, specifically defective photosensitive elements, and / or to compensate for the aging effect. For example, aging may be tracked based on the temperature-compensated detector impedance over usage time. Additionally or alternatively, in case the degradation quotient of the temperature-corrected detector impedance and the temperature-corrected reference impedance exceeds a predetermined threshold and / or differs from other degradation quotients of other photosensitive elements, an erroneous measurement and / or the displaying thereof may be prevented. If the item of degradation information may indicates a degraded photosensitive element for a predetermined period of time, a defective photosensitive element may be identified.

[0092] The temperature-corrected detector impedance may be obtained from measurement by accompanying analysis: The applied bias voltage to the photosensitive element may be either known or predetermined by the evaluation unit, e.g. using a control loop. The detector current may be a sum of the skimming current and the measurement current. Skimming of the detector current may specifically be performed have small signal current flow into the evaluation unit, i.e. the measurement cell, in order to determine the detector current much more precisely. For measuring under different conditions, e.g. different temperatures, a skimming algorithm may be performed to obtain the measurement current in an optimal range for the measurement circuit of the evaluation unit. The skimming algorithm may comprise determining if the measurement current is in a predefined range. A binary search over skimming bit may be implemented. The skimming algorithm may comprise determining the skimming current by determining the difference of the measurement current upon applying different skimming current settings. Thus, multiple measurements of the detector current may be conducted before the user-triggered measurement is even started. A dark resistance may thus be known before the measurement and may be used to detect degradation from aging and / or temperature hysteresis behavior.

[0093] The temperature-corrected reference impedance may be determined accompanying the determining of the temperature-corrected detector impedance. The determining of the temperature- corrected reference impedance may be performed using the same or equivalent circuit compared with the determining of the temperature-corrected detector impedance. The influence of conditions, e.g. temperature or the like, on the measurement circuit may be compensated. Additionally or alternatively, the known reference resistor may be used to determine the skimming current by comparing the detector current and the reference current.

[0094] Further, in case the photosensitive element may comprise a photodiode, the determining of the temperature-corrected detector impedance may be performed similar to a photoresistor but with different bias voltage. The skimming current may reduce a reverse current of the photodiode into the evaluation unit, specifically the measurement cell. The skimming algorithm may provide further information on a dark current of the photodiode.

[0095] Summarizing and without excluding further possible embodiments, the following embodiments may be envisaged: Embodiment 1 : A method for evaluating degradation of a photodetector, the photodetector comprising at least one photosensitive element, the photodetector being configured for generating at least one detector current depending on an illumination of the photosensitive element by light, the photodetector further comprising at least one evaluation unit for evaluating the detector current, wherein method comprises: a) determining at least one detector current; b) evaluating the detector current with respect to at least one reference value to obtain at least one relative detector current value; and c) deriving at least one item of degradation information on the photosensitive element using the relative detector current value, the item of degradation information describing the degradation of performance due to temperature hysteresis behavior, aging, excessive temperatures and / or excessive illumination.

[0096] Embodiment 2: The method according to the preceding embodiment, wherein the detector current comprises a dark detector current and a photocurrent.

[0097] Embodiment 3: The method according to any one of the preceding embodiments, wherein the detector current comprises a dark detector current, specifically a dark detector current without illumination of the photosensitive element by light, wherein the reference value comprises at least one calibration value, specifically at least one predetermined calibration value.

[0098] Embodiment 4: The method according to the preceding embodiment, wherein step b) further comprises a temperature correction of the dark detector current, wherein the temperature- corrected dark detector current is evaluated with respect to the reference value.

[0099] Embodiment 5: The method according to any one of the two preceding embodiments, wherein the relative detector current value comprises at least one degradation quotient using the dark detector current, specifically the temperature-corrected dark detector current, and the calibration value.

[0100] Embodiment 6: The method according to any one of the preceding embodiments, wherein the photodetector further comprises at least one reference resistor, the photodetector being configured for generating at least one reference current through the reference resistor, wherein the evaluation unit is configured for evaluating the reference current, wherein step a) comprises determining a dark detector current and the reference current through the reference resistor, wherein, in step b), the reference current is used as the reference value.

[0101] Embodiment 7: The method according to the preceding embodiment, wherein the evaluation unit comprises at least one printed circuit and / or at least one integrated circuit, wherein the reference resistor is part of the printed circuit or the integrated circuit Embodiment 8: The method according to the two preceding embodiments, wherein the relative detector current value comprises at least one degradation quotient using the dark detector current and the reference current.

[0102] Embodiment 9: The method according to any one of the three preceding embodiments, wherein step a) further comprises determining at least one temperature-corrected detector impedance of the photosensitive element from the detector current, wherein step a) further comprises determining at least one temperature-corrected reference impedance of the reference resistor from the reference current, wherein, in step b), the temperature-corrected reference impedance is used as the reference value, wherein the temperature-corrected detector impedance is evaluated with respect to the temperature-corrected reference impedance.

[0103] Embodiment 10: The method according to the preceding embodiments, wherein the relative detector current value comprises at least one degradation quotient using the temperature- corrected detector impedance and the temperature-corrected reference impedance.

[0104] Embodiment 11 : The method according to any one of the two preceding embodiments, wherein the photodetector further comprises at least one skimming circuit for skimming the detector current separating a measurement current to the evaluation unit and a skimming current to the skimming circuit.

[0105] Embodiment 12: The method according to the preceding embodiment, wherein the detector current is a sum of the measurement current and the skimming current.

[0106] Embodiment 13: The method according to any one of the two preceding embodiments, wherein the reference resistor is used to determine the skimming current by comparing the detector current and the reference current.

[0107] Embodiment 14: The method according to the three preceding embodiments, wherein a known or predetermined bias voltage is applied to the photosensitive element, wherein the temperature-corrected detector impedance is determined using the bias voltage, the measurement current and the skimming current.

[0108] Embodiment 15: The method according to any one of the four preceding embodiments, wherein a known or predetermined bias voltage is applied to the reference resistor, wherein the temperature-corrected reference impedance is determined using the bias voltage and the reference current. Embodiment 16: The method according to any one of the seven preceding embodiments, wherein the determining of the temperature-corrected detector impedance of the photosensitive element and the determining of the temperature-corrected reference impedance of the reference resistor is performed at least partially simultaneously.

[0109] Embodiment 17: The method according to any one of the eight preceding embodiments, wherein the temperature-corrected reference impedance is determined using the same or an equivalent circuit used for determining the temperature-corrected detector impedance.

[0110] Embodiment 18: The method according to any one of the preceding embodiments, wherein the photodetector is comprised by at least one spectrometer device, specifically is part of at least one spectrometer device, the spectrometer device comprising at least one light source for generating illumination light illuminating an object applied to at least one object interface of the spectrometer device, the spectrometer device further comprising at least one first optical path configured for allowing the illumination light to propagate to the photodetector by passing the object interface at least once, the spectrometer device further comprising at least one second optical path configured for allowing the illumination light to propagate to the photodetector without passing the object interface, wherein the method comprises in step a) determining at least one dark detector current and at least one illumination detector current via the second optical path, wherein, in step b), the illumination detector current is evaluated with respect to the dark detector current.

[0111] Embodiment 19: The method according to the preceding embodiment, wherein the dark detector current is determined having no illumination light on the photodetector via the second optical path, wherein the illumination detector current is determined with illumination of the photodetector by the light source via the second optical path.

[0112] Embodiment 20: The method according to any one of the two preceding embodiments, wherein step b) further comprises a temperature correction of the dark detector current and the illumination detector current, wherein the temperature-corrected illumination detector current is evaluated with respect to the temperature-corrected dark detector current.

[0113] Embodiment 21 : The method according to any one of the three preceding embodiments, wherein the illumination detector current is determined at a predefined or predetermined illumination power of the light source.

[0114] Embodiment 22: The method according to any one of the four preceding embodiments, wherein the relative detector current value comprises at least one degradation quotient using the illumination detector current, specifically the temperature-corrected illumination detector current, and the dark detector current, specifically the temperature-corrected dark detector current. Embodiment 23: The method according to any one of embodiments 5, 8, 10 or 22, wherein the item of degradation information indicates a degraded photosensitive element if the degradation quotient differs from a predetermined value by more than a given threshold, specifically by more than 20 % of the predetermined value, more specifically by more than 10 % of the predetermined value.

[0115] Embodiment 24: The method according to the preceding embodiment, the photodetector comprising a plurality of photosensitive elements, wherein the method is performed for each photosensitive element.

[0116] Embodiment 25: The method according to the preceding embodiment, wherein the deriving of the item of degradation information on the photosensitive element comprises comparing the degradation quotients of the plurality of photosensitive elements.

[0117] Embodiment 26: The method according to the preceding embodiment, wherein the item of degradation information indicates a degraded photosensitive element if a degradation quotient for the photosensitive element differs from at least one comparison degradation quotient of the plurality of photosensitive elements by more than a given threshold, wherein the comparison degradation quotient of the plurality of photosensitive elements comprises at least one of: a mean of the degradation quotients of the plurality of photosensitive elements, specifically an arithmetic mean of the degradation quotients of the plurality of photosensitive element; a minimum degradation quotient of the degradation quotients of the plurality of photosensitive elements; a maximum degradation quotient of the degradation quotients of the plurality of photosensitive elements.

[0118] Embodiment 27: The method according to any one of the four preceding embodiments, wherein the method comprises identifying a defective photosensitive element if the degradation quotient exceeds a number of 10, specifically a number of 5, more specifically a number of 2.

[0119] Embodiment 28: The method according to any one of the preceding embodiments, wherein, if the item of degradation information indicates a degraded photosensitive element, the method further comprises preventing displaying an erroneous measurement performed with the degraded photosensitive element.

[0120] Embodiment 29: The method according to any one of the preceding embodiments, wherein, if the item of degradation information indicates a degraded photosensitive element for a predetermined period of time, the method comprises identifying a defective photosensitive element.

[0121] Embodiment 30: The method according to any one of the preceding embodiments, wherein the item of degradation information comprises at least one item of information selected from the group consisting of: at least one item of aging information, specifically comprising information on an aging of the photosensitive element; at least one item of hysteresis information, specifically comprising information on a hysteresis of the photosensitive element, more specifically information on a temperature hysteresis of the photosensitive element; at least one item of excessive temperature information; at least one item of excessive illumination information, specifically comprising information on at least one excessive illumination of the photosensitive element in at least one of the visible spectral range, the infrared spectral range and the ultraviolet spectral range.

[0122] Embodiment 31 : The method according to any one of the preceding embodiments, wherein the photodetector comprises at least one temperature sensor for determining at least one temperature, specifically at least one temperature of the photosensitive element, wherein the method further comprises, specifically prior to step a) or at least partially simultaneously, determining at least one temperature, specifically at least one temperature of the photosensitive element.

[0123] Embodiment 32: The method according to the preceding embodiment, wherein the temperature is used to determine a temperature correction, specifically a temperature correction for one or more of the detector current or the reference current, more specifically a temperature correction comprising temperature compensation curves.

[0124] Embodiment 33: The method according to any one of the preceding embodiments, wherein the photosensitive element is at least one of a photoresistor and a photodiode.

[0125] Embodiment 34: The method according to any one of the preceding embodiments, wherein the photodetector further comprises at least one skimming circuit for skimming the detector current separating a measurement current to the evaluation unit and a skimming current to the skimming circuit, wherein step a) comprises determining both the measurement current and the skimming current, wherein the detector current is a sum of the measurement current and the skimming current.

[0126] Embodiment 35: The method according to any one of the preceding embodiments, wherein the method, specifically step b) and / or step c), is at least partially computer-implemented.

[0127] Embodiment 36: A photodetector comprising at least one photosensitive element, the photodetector being configured for generating at least one detector current depending on an illumination of the photosensitive element by light, wherein the photodetector further comprises at least one evaluation unit for evaluating the detector current, wherein the photodetector is configured for performing the method according to any one of the preceding embodiments.

[0128] Embodiment 37: The photodetector according to the preceding embodiment, further comprising at least one reference resistor, wherein the photodetector is configured for generating at least one reference current, wherein the evaluation unit is configured for evaluating the reference current.

[0129] Embodiment 38: A spectrometer device, specifically a portable spectrometer device, for obtaining spectroscopic information on at least one object, the spectrometer device comprising at least one photodetector according to the preceding embodiment.

[0130] Embodiment 39: The spectrometer device according to the preceding embodiment, further comprising at least one light source for generating illumination light illuminating the object applied to at least one object interface of the spectrometer device.

[0131] Embodiment 40: The spectrometer device according to the preceding embodiment, wherein the light source is configured for emitting light in a spectral range at least partially comprising an infrared spectral range, specifically a near-infrared spectral range, more specifically in a spectral range from 300 nm to 3 pm, more specifically in a spectral range from 760 nm to 3 pm, more specifically in a spectral range from 1 pm to 20 pm, more specifically in a spectral range from 1 pm to 2.5 pm, more specifically in a spectral range from 1.3 pm to 2.5 pm, most specifically in a spectral range from 1.5 pm to 2.2 pm.

[0132] Embodiment 41 : The spectrometer device according to any one of the two embodiments, wherein the light source comprises at least one light source selected from the group consisting of: an incandescent lamp; a light emitting diode (LED); a laser, a laser diode, a solid-state laser, a gas laser, a quantum cascade laser, a plasma light source.

[0133] Embodiment 42: The spectrometer device according to any one of the three preceding embodiment, further comprising at least one first optical path configured for allowing the illumination light to propagate to the photodetector by passing the object interface at least once, the spectrometer device further comprising at least one second optical path configured for allowing the illumination light to propagate to the photodetector without passing the object interface.

[0134] Embodiment 43: The spectrometer device according to any one of the preceding embodiments referring to a spectrometer device, further comprising at least one wavelength-selective element for selectively transferring detection light from the object to the photodetector.

[0135] Embodiment 44: A computer program comprising instructions which, when the program is executed by a photodetector according to any one of the preceding embodiments referring to a photodetector, cause the photodetector to perform the method according to any one of the preceding embodiments referring to a method.

[0136] Embodiment 45: A computer-readable storage medium, specifically a non-transient computer- readable storage medium, comprising instructions which, when the instructions are executed by a photodetector according to any one of the preceding embodiments referring to a photodetector, cause the photodetector to perform the method according to any one of the preceding embodiments referring to a method.

[0137] Short description of the Figures

[0138] Further optional features and embodiments will be disclosed in more detail in the subsequent description of embodiments, preferably in conjunction with the dependent claims. Therein, the respective optional features may be realized in an isolated fashion as well as in any arbitrary feasible combination, as the skilled person will realize. The scope of the invention is not restricted by the preferred embodiments. The embodiments are schematically depicted in the Figures. Therein, identical reference numbers in these Figures refer to identical or functionally comparable elements.

[0139] In the Figures:

[0140] Figure 1 shows a first embodiment of a spectrometer device and of a photodetec- tor in a schematic view; and

[0141] Figures 2A and 2B show exemplary embodiments of the photodetector;

[0142] Figure 3 shows a flow chart of a method for evaluating degradation of a photodetector;

[0143] Figure 4 shows a diagram of a resistance of a photoresistor as a function of temperature;

[0144] Figure 5 shows a second embodiment of a spectrometer device and of a photodetector in a schematic view; and

[0145] Figure 6 shows a third embodiment of a spectrometer device and of a photodetector in a schematic view.

[0146] Detailed description of the embodiments

[0147] Figure 1 shows a first exemplary embodiment of a spectrometer device 110 and of a photodetector 112 in a schematic view. As shown in Figure 1 , in this exemplary embodiment, the photodetector 112 is comprised by the spectrometer device 110. However, the photodetector 112 according to the present invention may also be used separately from the spectrometer device 110, such as in the field of flame monitoring, flame and spark detection, gas sensing and / or moisture monitoring. Other fields of application are also feasible. The spectrometer device 110 may specifically be a portable spectrometer device, such as a spectrometer device 110 being part of a mobile device or being attachable to a mobile device (not shown in Figure 1 ), such as a notebook computer, a tablet, a cell phone, such as a smartphone, a smartwatch and / or a wearable computer.

[0148] The spectrometer device 110 is configured for obtaining spectroscopic information on at least one object 114. Specifically, as shown in Figure 1 , the spectrometer device 110 may be a diffusive reflective spectrometer device configured for acquiring spectral information from light which is diffusively reflected by the at least one object 114, e.g. at least one sample. Additionally or alternatively, the at least one spectrometer device 110 may be or may comprise an absorption- and / or transmission spectrometer. In particular, measuring a spectrum with the spectrometer device 110 may comprise measuring absorption in a transmission configuration. Specifically, the spectrometer device 110 may be configured for measuring absorption in a transmission configuration. However, other types of spectrometer devices 110 are also feasible.

[0149] The spectrometer device 110 comprises the at least one photodetector 112 according to the present invention. The photodetector 112 comprises at least one photosensitive element 116. In this example, as shown in Figure 1 , the photodetector 112 may specifically comprise a plurality of photosensitive elements 116. Specifically, the photodetector 112 may be or may comprise at least one detector array 118, the detector array 118 specifically comprising an array of the plurality of photosensitive elements 116. The photodetector 112 is configured for generating at least one detector current depending on an illumination of the photosensitive element 116 by light. The photodetector 112, in this example, may further comprise at least one reference resistor 122. The photodetector 112 may be configured for generating at least one reference current. The photodetector 112 further comprises at least one evaluation unit 120 for evaluating the detector current and, optionally, the reference current. A detailed view of the photodetector 112, specifically of measurement channels of the photodetector 112, is shown in Figures 2A and 2B. However, other embodiments of the photodetector 112 described herein may also be feasible.

[0150] The photodetector 112 is configured for performing the method according to the present invention, such as according to the embodiment described with respect to Figure 3 and / or according to any other embodiment disclosed herein. Thus, for a description of the method for evaluating degradation of the photodetector 112, reference is made to the description of Figure 3 below.

[0151] The spectrometer device 110 may further comprise at least one light source 124 for generating illumination light 126 illuminating the object 114. The light source 124 may be configured for emitting light in a spectral range at least partially comprising the infrared spectral range, specifically the near-infrared spectral range, more specifically in a spectral range from 300 nm to 3 pm, more specifically in a spectral range from 760 nm to 3 pm, more specifically in a spectral range from 1 pm to 20 pm, more specifically in a spectral range from 1 pm to 2.5 pm, more specifically in a spectral range from 1 .3 pm to 2.5 pm, most specifically in a spectral range from 1 .5 pm to 2.2 pm. For example, the light source 124 may comprise at least one light source selected from the group consisting of: an incandescent lamp; a light emitting diode (LED); a laser, a laser diode, a solid-state laser, a gas laser, a quantum cascade laser, a plasma light source. For example, the light source 124 may comprise a blue light LED having a primary light emission at 440 nm and, optionally, further comprising at least one luminescent material for at least partially converting the primary light at least partially into light the infrared spectral range, specifically the near-infrared spectral range, e.g. a phosphor luminescent material. Other examples of the light source 124 are, however, also feasible.

[0152] Further, as shown in Figure 1 , the spectrometer device 110 may comprise at least one wave- length-selective element 128 for selectively transferring detection light 130 from the object 114 to the photodetector 112. The wavelength-selective element 128 may specifically be arranged in a beam path of the detection light, such as in a beam path in between the object 114 and the photodetector 112. The wavelength-selective element 128 specifically may be selected from the group of a tunable wavelength-selective element and a wavelength-selective element having a fixed transmission spectrum. By using a tunable wavelength-selective element, as an example, differing wavelength ranges may be selected sequentially, whereas, by using a wavelength-selective element having a fixed transmission spectrum, the selection of the wavelength ranges may be fixed and may, however, be dependent e.g. on a detection position, thereby allowing, as an example, for simultaneously exposing photodetectors 112 and / or different photosensitive elements 116 of the photodetector 112 to differing spectral ranges of light.

[0153] The wavelength-selective element 128 may comprise at least one of a filter, a grating, a prism, a plasmonic filter, a diffractive optical element and a metamaterial. The wavelength-selective element 128 may comprise one or more of a dispersive (e.g. prism), or diffractive (grating) element, or a detector with an inherently limited bandwidth of its spectral response. Additionally or alternatively, the wavelength-selective element 128 may comprise at least one of the following elements: an array of individual bandpass filters, an array of patterned filters, a MEMS-lnterfer- ometer, a MEMS-Fabry Perot interferometer. Further elements are feasible.

[0154] Further, as schematically shown in Figure 1 , the photodetector 112 may further comprise at least one temperature sensor 131 for determining at least one temperature, specifically at least one temperature of the photosensitive element 116. The temperature may be used, for example, for determining temperature-corrected quantities with the photodetector 112, as will be outlined in further detail below.

[0155] Figures 2A and 2B show exemplary embodiments of the photodetector 112. Specifically, Figures 2A and 2B show exemplary embodiments of a measurement channel 132 of the photodetector 112 for a photoresistor 134 (Figure 2A) and a photodiode 136 (Figure 2B).

[0156] As shown in Figures 2A and 2B, the photodetector 112, specifically the measurement channel 132 of the photodetector 112, may further comprise at least one skimming circuit 138 for skimming the detector current (denoted as ID in Figures 2A and 2B) separating a measurement current (denoted as lmin Figures 2A and 2B) to the evaluation unit 120 and a skimming current (denoted as lsin Figures 2A and 2B) to the skimming circuit 138. The skimming circuit 138 may be an arbitrary electric circuit configured for skimming the detector current. As can be seen in Figures 2A and 2B, the detector current may be a sum of the measurement current and the skimming current.

[0157] Further, a known or predetermined bias voltage (denoted as Vb in Figures 2A and 2B) may be applied to the photosensitive element 116. For example, an absolute value of the bias voltage applied to the photodiode 136 may be in the range of 0 V to 10 V, specifically in the range of 0 V to 8V, more specifically in the range of 0.5 V to 2 V. As an example, the photodiode 136 may be operated with zero bias voltage. Alternatively, the photodiode 136 may be operated with a reverse bias voltage, i.e. a negative bias voltage having an absolute value in the range of 0 V to 10 V, specifically in the range of 0 V to 8 V, more specifically in the range of 0.5 V to 2 V. The bias voltage applied to a photoresistor 134 may be dependent on the resistance of the photoresistor 134. The bias voltage applied to the photoresistor 134 may be in the range of 0 V to 50 V, specifically in the range of 1 V to 20 V, more specifically in the range of 1 V to 10 V. Alternatively, an alternating bias voltage may be applied to the photoresistor 134, specifically having an amplitude in the range of 0 V to 50 V, specifically in the range of 1 V to 20 V, more specifically in the range of 1 V to 10 V. The detector impedance (denoted as RD in Figures 2A and 2B), specifically the temperature-corrected detector impedance as will be outlined in further detail below, may be determined using the bias voltage, the measurement current and the skimming current.

[0158] As indicated in Figure 2A, the measurement channel 132 for the references resistor 122 may be an equivalent circuit compared to the measurement channel 132 for the photosensitive element 116, specifically the photoresistor 134. Thus, in the measurement channel 132 for the references resistor 122, the reference resistor 122 may replace the photosensitive element 116, specifically the photoresistor 134. Similar to the measurement channel 132 for the photoresistor 134, a known or predetermined bias voltage may be applied to the reference resistor 122. The reference impedance of the reference resistor 122, specifically the temperature-corrected reference impedance as will be outlined in further detail below, may be determined using the bias voltage and the reference current. Thus, the evaluation unit 120 may be configured for evaluating both the detector current from the photosensitive element 116 and the current from the reference resistor 122. The evaluation unit 120, specifically the printed or integrated circuit of the evaluation unit 120, may be configured, e.g. by using one or more electronic or digital switches, for receiving the detector current from the photosensitive element 116 or, alternatively, from the reference resistor 122. Alternatively, however, the evaluation unit 120 may also be configured for receiving the detector current from both the photosensitive element 116 and the reference resistor 122.

[0159] Figure 3 shows a flow chart of a method for evaluating degradation of a photodetector 112, specifically of a photosensitive element 116. The photodetector 112 used in the method comprises at least one photosensitive element 116 and is configured for generating at least one detector current depending on an illumination of the photosensitive element 116 by light. The photodetector 112, in this exemplary embodiment, may further comprise at least one reference resistor 122 as shown in Figure 1 and may be configured for generating at least one reference current. The photodetector 112 further comprises at least one evaluation unit 120 for evaluating the detector current and, optionally, the reference current. An exemplary embodiment of the photodetector 112 used in the method is shown in Figure 1 . Thus, for a detailed description of the photodetector 112, reference is made to the description of Figure 1. However, other embodiments of the photodetector 112 to be used in the method are also feasible.

[0160] The method comprises the following steps that may be performed in the given order. However, a different order may also be possible. In particular, one, more than one or even all of the method steps may be performed once or repeatedly. Further, the method steps may be performed successively or, alternatively, one or more of the method steps may be performed in a timely overlapping fashion or even in a parallel fashion and / or in a combined fashion. For example, step a) may be performed at least partially simultaneously to step b). The method may further comprise additional method steps that are not listed.

[0161] The method comprises: a) (denoted by reference number 140) determining at least one detector current; b) (denoted by reference number 142) evaluating the detector current with respect to at least one reference value to obtain at least one relative detector current value; and c) (denoted by reference number 144) deriving at least one item of degradation information on the photosensitive element 116 using the relative detector current value, the item of degradation information describing the degradation of performance due to temperature hysteresis behavior, aging, excessive temperatures and / or excessive illumination.

[0162] As outlined above, the photodetector 112, as an example, may further comprise the at least one temperature sensor 131 for determining at least one temperature, specifically at least one temperature of the photosensitive element 116. The method may further comprise, specifically prior to step a) or at least partially simultaneously, determining at least one temperature, specifically at least one temperature of the photosensitive element 116. The temperature may be used to determine a temperature correction, specifically a temperature correction for one or more of the detector current and a reference current, more specifically a temperature correction comprising temperature compensation curves. For example, Figure 4 shows a diagram of a resistance 146 of a photoresistor 134 as a function of temperature 148. The temperature curve shown in Figure 4 may be known or predetermined for the photosensitive element 116 and / or the reference resistor 122. The temperature curve may be stored and used for temperature correction. In the method, the temperature correction may specifically be performed after determining the detector current, specifically the detector current through the photosensitive element 116, and / or the determining of the reference current through reference resistor 122, respectively.

[0163] As an example, as outlined above, the photodetector 112 may be configured for generating at least one reference current through the reference resistor 122. The evaluation unit 120 may be configured for evaluating the reference current. Specifically, step a) may comprise determining a dark detector current and the reference current through the reference resistor 122. Further, in step b), the reference current may be used as the reference value. The relative detector current value may comprise at least one degradation quotient using the dark detector current and the reference current. The reference resistor 122, as an example, may have an essentially identical temperature dependency to the photosensitive element 116. Thus, in this example, the detector current may be evaluated with respect to the reference current without any temperature correction. Alternatively or additionally, specifically in case the temperature dependence of the resistance of the reference resistor 122 is different from the temperature dependence of the resistance of the photosensitive element 116, step b) may comprise a temperature correction of the dark detector current and the reference current. The temperature-corrected dark detector current may be evaluated with respect to the temperature-corrected reference current. Thus, in this example, the relative detector current value may comprise a degradation quotient using the temperature-corrected dark detector current and the temperature-corrected reference current.

[0164] Figure 5 shows a second exemplary embodiment of the spectrometer device 110 and of the photodetector 112 in a schematic view. The spectrometer device 110 and the photodetector 112 as shown in Figure 5 widely correspond to the first embodiment of the spectrometer device 110 and the photodetector shown in Figure 1 . Thus, for a detailed description of this second embodiment, reference is made to the description of Figure 1.

[0165] In this exemplary embodiment, as can be seen in Figure 5, the photodetector 112 may not have a reference resistor 122. The degradation of this exemplary embodiment may be evaluated by using the detector current only. As an example, in the method for evaluating degradation of a photodetector 112, the detector current may comprise a dark detector current, specifically a dark detector current without illumination of the photosensitive element 116 by light. The reference value may comprise at least one calibration value, specifically at least one predetermined calibration value. The calibration value may be predefined or predetermined and, specifically, may be kept constant during the method and / or usage of the photodetector 112. The relative detector current value may comprise at least one degradation quotient using the dark detector current and the calibration value. Step b) may comprise a temperature correction of the dark detector current. The temperature-corrected dark detector current may be evaluated with respect to the reference value. Thus, in this example, the relative detector current value may comprise a degradation quotient using the temperature-corrected dark detector current and the calibration value.

[0166] Figure 6 shows a third exemplary embodiment of a spectrometer device 110 and of a photodetector 112 in a schematic view. The spectrometer device 110 and the photodetector 112 as shown in Figure 6 widely correspond to the first and / or second embodiment of the spectrometer device 110 and the photodetector shown in Figures 1 and 5. Thus, for a detailed description of this third embodiment, reference is made to the description of Figures 1 and / or 5.

[0167] As can be seen in Figure 6, the spectrometer device 110 may comprise the at least one light source 124 for generating illumination light 126 illuminating the object 114 applied to at least one object interface 152 of the spectrometer device 110. The spectrometer device 110 may further comprise at least one first optical path 154 configured for allowing the illumination light 126 to propagate to the photodetector 112 by passing the object interface 152 at least once. The spectrometer device 110 may further comprise at least one second optical path 156 configured for allowing the illumination light 126 to propagate to the photodetector 112 without passing the object interface 152. The method may comprise in step a) determining at least one dark detector current and at least one illumination detector current via the second optical path 156. Further, in step b), the illumination detector current may be evaluated with respect to the dark detector current.

[0168] The dark detector current may specifically be determined having no illumination light on the photodetector 112 via the second optical path 156. The illumination detector current may specifically be determined with illumination of the photodetector 112 by the light source 124 via the second optical path 156. The illumination detector current may be determined at a predefined or predetermined illumination power of the light source 124.

[0169] Further, optionally, step b) may comprise a temperature correction of the dark detector current and the illumination detector current. The temperature-corrected illumination detector current may be evaluated with respect to the temperature-corrected dark detector current.

[0170] The relative detector current value may comprise at least one degradation quotient using the illumination detector current, specifically the temperature-corrected illumination detector current, and the dark detector current, specifically the temperature-corrected dark detector current.

[0171] In the exemplary embodiment of Figure 6, the spectrometer device 110 may comprise one light source 124 configured for emitting the illumination light 126 into the first optical path 154 and the second optical path 156. The second optical path, as an example, may comprise at least one internal reflection target 158, wherein the illumination light 126 emitted from the light source 124 via the second optical path 156 may be passed to the internal reflection target 158 and subsequently to the photodetector 112 without interacting with the object 114 at the object interface 152. Alternatively or additionally, the spectrometer device 110 may also comprise at least two light sources 124, wherein at least one of the light sources 124 is arranged in each of the first optical path 154 and the second optical path 156. The light source 124 in the second optical path 156 may optionally be arranged to directly illuminate photodetector 112.

[0172] Further, as outlined above, the photodetector 112 may comprise a plurality of photosensitive elements 116. The method may performed for each photosensitive element 116. For example, the method may be performed for each photosensitive element 166 individually, such as for each photosensitive element 116 independently from the other photosensitive elements 116. Alternatively or additionally, the deriving of the item of degradation information on the photosensitive element 116 may comprise comparing the degradation quotients of the plurality of photosensitive elements 116. The item of degradation information may indicate a degraded photosensitive element 116 if a degradation quotient for the photosensitive element 116 differs from at least one comparison degradation quotient of the plurality of photosensitive elements 116 by more than a given threshold. The comparison degradation quotient of the plurality of photosensitive elements 116 may comprise at least one of: a mean of the degradation quotients of the plurality of photosensitive elements 116, specifically an arithmetic mean of the degradation quotients of the plurality of photosensitive elements 116; a minimum degradation quotient of the degradation quotients of the plurality of photosensitive elements 116; a maximum degradation quotient of the degradation quotients of the plurality of photosensitive elements 116. For example, the degradation quotient of one the photosensitive elements 116 may be compared to an arithmetic mean of the degradation quotients of the plurality of photosensitive elements 116 to derive the item of degradation information on the photosensitive element 116. The comparing may specifically be performed in case the photodetector 112 may comprise a number of photosensitive elements 116 for which the arithmetic mean of the degradation quotient may not be influenced by one degraded photosensitive element 116, e.g. for a number of 16 photosensitive elements 116 or more. Alternatively or additionally, as another example, the degradation quotient of one photosensitive element 116 may be compared to one or both of a maximum degradation quotient and a minimum degradation quotient of the degradation quotients of the plurality of photosensitive elements 116 to derive the item of degradation information on the photosensitive element 116, specifically in case the number of photosensitive elements may be less than 16.

[0173] The method may further comprise identifying a defective photosensitive element 116 if the degradation quotient exceeds a number of 10, specifically a number of 5, more specifically a number of 2 (denoted by reference number 150 in Figure 3). For example, in case of a reference resistor 122, the resistance of the reference resistor 122 may be chosen to be equal to a resistance of the photosensitive element 116 at a standard or reference temperature, specifically at least within an error range of the respective resistance values. As outlined above, the bias voltage may be applied to both the photosensitive element 116 and the reference resistor 122 to determine the detector current and the reference current, respectively. The degradation quotient using the dark detector current and the reference current may be equal to unity at the standard or reference temperature, specifically for non-degraded photosensitive elements 116. Alternatively or additionally, the calibration value may be determined in accordance with a dark current value of the photodetector in a pristine state of the photodetector 112 at a standard or reference temperature. The degradation quotient using the dark detector current and the calibration value may be equal to unity at the standard or reference temperature, specifically for non-degraded photosensitive elements 116. Alternatively or additionally, in general, it may be possible to determine the degradation quotient such that the degradation quotient is equal to unity for a nondegraded photosensitive element 116, e.g. by using one or more normalization factors. In any case, if the degradation quotient differs by more than a given threshold, e.g. by more than 20 %, from unity, a degraded photodetector 112, specifically a degraded photosensitive element 116, may be determined. In case the degradation quotient exceeds a factor of 2, the photodetector 112, specifically the photosensitive element 116 may be determined defective. Thus, it may be important to monitor the degradation quotient for the photodetector 112, specifically for the photosensitive element 116, in order to avoid having the photodetector 112, specifically the photosensitive element 116, in a defective state. The method may comprise, if the item of degradation information indicates a degraded photosensitive element 116, preventing displaying an erroneous measurement performed with the degraded photosensitive element 116. Alternatively or additionally, the method may comprise, if the item of degradation information indicates a degraded photosensitive element 116 for a predetermined period of time, identifying a defective photosensitive element 116.

[0174] List of reference numbers spectrometer device photodetector object photosensitive element detector array evaluation unit reference resistor light source illumination light wavelength-selective element detection light temperature sensor measurement channel photoresistor photodiode skimming circuit determining at least one temperature-corrected detector impedance determining at least one temperature-corrected reference impedance deriving at least one item of degradation information resistance temperature identifying a defective photosensitive element object interface first optical path second optical path

Claims

Claims1 . A method for evaluating degradation of a photodetector (112), the photodetector (112) comprising at least one photosensitive element (116), the photodetector (112) being configured for generating at least one detector current depending on an illumination of the photosensitive element (116) by light, the photodetector (112) further comprising at least one evaluation unit (120) for evaluating the detector current, wherein method comprises: a) determining at least one detector current; b) evaluating the detector current with respect to at least one reference value to obtain at least one relative detector current value; and c) deriving at least one item of degradation information on the photosensitive element (116) using the relative detector current value, the item of degradation information describing the degradation of performance due to temperature hysteresis behavior, aging, excessive temperatures and / or excessive illumination.

2. The method according to the preceding claim, wherein the detector current comprises a dark detector current, wherein the reference value comprises at least one calibration value, wherein the relative detector current value comprises at least one degradation quotient using the dark detector current.

3. The method according to any one of the preceding claims, wherein the photodetector(112) further comprises at least one reference resistor (122), the photodetector (112) being configured for generating at least one reference current through the reference resistor (122), wherein the evaluation unit (120) is configured for evaluating the reference current, wherein step a) comprises determining a dark detector current and the reference current through the reference resistor (122), wherein, in step b), the reference current is used as the reference value.

4. The method according to the preceding claim, wherein the relative detector current value comprises at least one degradation quotient using the dark detector current and the reference current.

5. The method according to any one of the two preceding claims, wherein step a) further comprises determining at least one temperature-corrected detector impedance of the photosensitive element (116) from the detector current, wherein step a) further comprises determining at least one temperature-corrected reference impedance of the reference resistor (122) from the reference current, wherein, in step b), the temperature-corrected reference impedance is used as the reference value, wherein the temperature-corrected detector impedance is evaluated with respect to the temperature-corrected reference impedance, wherein the relative detector current value comprises at least one degradation quotient using the temperature-corrected detector impedance and the temperature-corrected reference impedance.

6. The method according to any one of the preceding claims, wherein the photodetector (112) is comprised by at least one spectrometer device (110), the spectrometer device (110) comprising at least one light source (124) for generating illumination light (126) illuminating an object (114) applied to at least one object interface (152) of the spectrometer device (110), the spectrometer device (110) further comprising at least one first optical path (154) configured for allowing the illumination light (126) to propagate to the photodetector (112) by passing the object interface (152) at least once, the spectrometer device (110) further comprising at least one second optical path (156) configured for allowing the illumination light (126) to propagate to the photodetector (112) without passing the object interface (152), wherein the method comprises in step a) determining at least one dark detector current and at least one illumination detector current via the second optical path (156), wherein, in step b), the illumination detector current is evaluated with respect to the dark detector current, wherein the relative detector current value comprises at least one degradation quotient using the illumination detector current and the dark detector current.

7. The method according to any one of claims 2, 4, 5 or 6, wherein the item of degradation information indicates a degraded photosensitive element (116) if the degradation quotient differs from a predetermined value by more than a given threshold.

8. The method according to the preceding claim, the photodetector (112) comprising a plurality of photosensitive elements (116), wherein the method is performed for each photosensitive element (116), wherein the deriving of the item of degradation information on the photosensitive element (116) comprises comparing the degradation quotients of the plurality of photosensitive elements (116), wherein the item of degradation information indicates a degraded photosensitive element (116) if a degradation quotient for the photosensitive element (116) differs from at least one comparison degradation quotient of the plurality of photosensitive elements (116) by more than a given threshold, wherein the comparison degradation quotient of the plurality of photosensitive elements (116) comprises at least one of: a mean of the degradation quotients of the plurality of photosensitive elements (116); a minimum degradation quotient of the degradation quotients of the plurality of photosensitive elements (116); a maximum degradation quotient of the degradation quotients of the plurality of photosensitive elements (116).

9. The method according to any one of the preceding claims, wherein, if the item of degradation information indicates a degraded photosensitive element (116), the method further comprises preventing displaying an erroneous measurement performed with the degraded photosensitive element (116).

10. The method according to any one of the preceding claims, wherein, if the item of degradation information indicates a degraded photosensitive element (116) for a predetermined period of time, the method comprises identifying a defective photosensitive element (116).11 . The method according to any one of the preceding claims, wherein the item of degradation information comprises at least one item of information selected from the group consisting of: at least one item of aging information; at least one item of hysteresis information; at least one item of excessive temperature information; at least one item of excessive illumination information.

12. A photodetector (112) comprising at least one photosensitive element (116), the photodetector (112) being configured for generating at least one detector current depending on an illumination of the photosensitive element (116) by light, wherein the photodetector (112) further comprises at least one evaluation unit (120) for evaluating the detector current, wherein the photodetector (112) is configured for performing the method according to any one of the preceding claims.

13. A spectrometer device (110) for obtaining spectroscopic information on at least one object (114), the spectrometer device (110) comprising at least one photodetector (112) according to the preceding claim.

14. A computer program comprising instructions which, when the program is executed by a photodetector (112) according to any one of the preceding claims referring to a photodetector (112), cause the photodetector (112) to perform the method according to any one of the preceding claims referring to a method.

15. A computer-readable storage medium comprising instructions which, when the instructions are executed by a photodetector (112) according to any one of the preceding claims referring to a photodetector (112), cause the photodetector (112) to perform the method according to any one of the preceding claims referring to a method.

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