Spectrometer with a large spot size

Abstract

A portable optical device (100) that provides a large spot size spectrometer. The optical device includes an optical head (102), an optical window (106), and a spectrometer (104). The optical head (102) includes a plastic molded part (105) having an aperture (115) and a plurality of reflectors (112) around the aperture (115) formed in the plastic molded part. Each reflector (130) can include a respective lamp (110) assembled therein. The optical window (106) is configured to receive a sample (108), pass input light (128) from the lamp (130) to the sample (108), and pass scattered light from the sample (108) toward the aperture (115). The aperture (115) is configured to filter a first portion of the scattered light that contains unusable sample information and pass a second portion of the scattered light to the spectrometer (104).

Description

Technical Field

[0001] The techniques described below generally relate to optical spectroscopy, including diffuse reflectance infrared spectroscopy, and more particularly to a mechanism for enlarging the spot size of a spectrometer.

[0002] Cross - reference to related applications This application claims the priority and benefit of non - provisional application No. 17 / 828,747, filed with the United States Patent and Trademark Office on May 31, 2022, and provisional application No. 63 / 195,696, filed with the United States Patent and Trademark Office on June 1, 2021. The entire contents of those applications are hereby incorporated by reference into this specification as if fully set forth herein in their entirety for all applicable purposes.

Background Art

[0003] A spectrometer measures a single - beam spectrum (e.g., power spectral density (PSD)). The intensity of a single - beam spectrum is proportional to the power of the radiation reaching the detector. Diffuse reflectance spectroscopy can be used to study the molecular structure of a given substance based on its spectral response. In diffuse reflectance spectroscopy, a light source (e.g., a broadband light source) directs incident light onto a substance. The incident light interacts with the substance, and as a result, part of the light is transmitted, another part is reflected, and another part is scattered. The scattered part is affected by the absorption spectrum of the sample and can be used to identify the substance based on its spectral fingerprint. Diffuse reflectance spectroscopy can be used for substances in various forms, such as solids, powders, and liquids.

[0004] Various types of diffuse reflectance samples can exhibit different interactions with incident light, depending on the sample's shape, scattering characteristics, and absorption cross-section. For example, samples can be broadly classified into two types. The first type includes homogeneous and uniformly packed samples, where the sample particles are sufficiently small and uniformly distributed throughout the sample area. In homogeneous samples, there is no spectral variation in scattering and absorption characteristics between different locations in the sample. Furthermore, the sample completely and uniformly covers the optical window, so there may be no observable gaps between the window and the sample. Most liquids and powders fall into this category. The second type includes heterogeneous and randomly packed samples, where the sample consists of relatively large particles with dimensions of several millimeters. Scattering and absorption characteristics can differ even within the same particle and from particle to particle. Furthermore, the particles may have irregular shapes and be randomly arranged on the optical window with different orientations and non-uniform packing. This creates gaps between different particles. Generally, some light leaks through the gaps, and the remaining light strikes the particles at different locations, which can lead to measurement errors and / or low diffuse reflectance power. Examples of heterogeneous samples include grain and feed samples.

[0005] Small (e.g., handheld) near-infrared (NIR) spectrometers have limited light spot size, typically smaller than 3 mm in diameter. In this case, the system needs to be equipped with accessories to perform spatial averaging, such as a rotating sampling cup or Petri dish. However, this comes at the expense of measurement time and the overall complexity of the measurement system. [Overview of the project]

[0006] Below is an overview of one or more aspects of the Disclosure to provide a basic understanding of such aspects. This overview is not intended to be a comprehensive overview of all features under consideration in the Disclosure, nor to identify essential or important elements of all aspects of the Disclosure, nor to define the scope of any or all aspects of the Disclosure. Its sole purpose is to present some concepts of one or more aspects of the Disclosure in the form of a prelude to more detailed descriptions presented later.

[0007] Various aspects of this disclosure relate to mechanisms for increasing the spot size of a miniature spectrometer. Examples relate to optical devices including a micro-electromechanical system (MEMS) based Fourier transform infrared (FTIR) spectrometer having a light spot size of 3 mm to 20 mm operating over a spectral range of 1350 nm to 2500 nm. The optical device further includes an optical head comprising a plurality of miniature filament-based incandescent lamps and a reflective optics (e.g., reflectors) surrounding the lamps for illumination. The lamps are positioned in specific locations relative to the sample to provide a large spot size (e.g., a large sample illumination pattern), while retaining elements (e.g., plastic molded parts) are used to hold the lamps and reflectors in place. For example, the reflectors may be formed within plastic molded parts and coated with a metal coating, while the lamps may be assembled within the reflectors. The plastic molded parts may further include apertures configured to allow scattered light from the sample to pass through the spectrometer while limiting unwanted coupled rays to the spectrometer, in order to maximize coupling efficiency based on the spot size. In some examples, plastic molded parts are further used to hold an optical coupling element (e.g., a lens) responsible for collecting scattered light from the sample. The optical device may further include a protective transparent optical window that covers the optical head and provides an optical interface with the sample. In some examples, the optical head is assembled with the spectrometer package using positioning pins to maintain alignment errors at a negligible level.

[0008] In one example, an optical device is disclosed. This optical device comprises an optical head including a plastic molded part, an aperture formed in the plastic molded part, a plurality of reflectors formed around the aperture in the plastic molded part, and a plurality of lamps, each lamp of the plurality of lamps being assembled in one of the plurality of reflectors. The optical device further includes an optical window positioned on the optical head. The optical window is configured to receive a sample, allow input light from the plurality of lamps to pass through the sample, and allow scattered light scattered from the sample to pass through the aperture. The aperture has a shape and diameter configured to filter a first portion of the scattered light and allow a second portion of the scattered light to pass through, the first portion of the scattered light containing unusable sample information. The optical device further includes a spectrometer configured to receive the second portion of the scattered light at an input and obtain a spectrum of the sample based on the second portion of the scattered light.

[0009] These and other aspects of the present invention will be better understood by considering the following detailed description. Other aspects, features and embodiments of the present invention will become apparent to those skilled in the art by considering the following description of specific exemplary embodiments of the present invention in conjunction with the accompanying drawings. Features of the present invention may be described with respect to the following specific embodiments and drawings, but all embodiments of the present invention may include one or more of the advantageous features described herein. In other words, one or more embodiments may be described as having a particular advantageous feature, while one or more such features may be used according to the various embodiments of the present invention described herein. Similarly, exemplary embodiments may be described below as embodiments of devices, systems, or methods, but it should be understood that such exemplary embodiments can be implemented in a variety of devices, systems, and methods. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 shows an optical device including an optical head and a spectrometer with a large spot size according to several embodiments. [Figure 2] Figures 2A and 2B show examples of optical heads of optical devices according to several embodiments. [Figure 3] Figures 3A and 3B show an optical device including the optical head shown in Figures 2A and 2B, relating to several embodiments. [Figure 4] Figures 4A and 4B show another example of an optical head of an optical device according to several embodiments. [Figure 5] Figure 5 shows an example of an optical device including the optical head shown in Figures 4A and 4B, relating to several embodiments. [Figure 6] Figure 6 shows another example of an optical device including the optical head shown in Figures 4A and 4B, relating to several embodiments. [Figure 7] Figures 7A to 7C show examples of optical filtering by apertures in optical heads according to several embodiments. [Figure 8] Figures 8A and 8B show examples of optical windows for optical devices according to several embodiments. [Figure 9] Figures 9A to 9C show examples of spot sizes for spectrometers in several embodiments. [Figure 10] Figure 10 shows an example of an optical coupling element in an optical head according to several embodiments. [Figure 11] Figure 11 shows design curves for spot size based on the distance between the sample and the optical coupling element, relating to several embodiments. [Figure 12] Figure 12 shows examples of the configurations of various components of an optical head according to several embodiments. [Figure 13] Figures 13A to 13C show exemplary processes for measuring the spot size of a spectrometer according to several embodiments. [Modes for carrying out the invention]

[0011] The detailed descriptions provided below in relation to the attached drawings are intended to illustrate various configurations and are not intended to show only the configurations in which the concepts described herein can be implemented. The detailed descriptions include specific details to provide a complete understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts can be implemented without specific details. Sometimes, well-known structures and components are shown in block diagram form to avoid obscuring such concepts.

[0012] Figure 1 shows an optical device 100 comprising an optical head 102 and a spectrometer 104 with a large spot size, relating to several embodiments. In some examples, the optical device may be a portable handheld device. The optical device 100 further includes an optical window 106 configured to receive a sample 108 (e.g., a grain or feed sample). The optical head 102 includes an illumination unit 105 containing a plurality of lamps 110 (e.g., incandescent lamps), each lamp being assembled in one of a plurality of reflectors 112. The optical window 106 allows incident light 128 from the illumination unit 105 to pass through the sample 108. The incident light 128 interacts with the sample 108, resulting in some of the light being transmitted, another portion being reflected, and yet another portion being scattered by the sample 108. The scattered light 130 is influenced by the absorption spectrum of the sample and can be used to identify the sample 108.

[0013] The light 128 emitted from each lamp 110 is distributed across the entire solid angle. Each reflector 112 redirects the light from the corresponding lamp 110 towards the sample 108, forming an illumination pattern with a desired light spot size 135 on the sample 108. The number of lamps 110 and corresponding reflectors 112 is variable and can be selected, for example, based on the desired light spot size 135. For example, the optical head 102 may contain 3 to 7 lamps 110 to achieve a spot size diameter of 3 mm to 20 mm operating over a spectral range of 1350 nm to 2500 nm. The number of lamps 110 can be further selected to control the intensity profile and prevent overheating of the sample 108. Positioning the lamps 110 relative to the sample 108 to distribute the light emitted to different points in the sample space provides further flexibility in achieving the desired target illumination pattern.

[0014] In some examples, the optical head 102 may be a plastic molded part including an illumination unit 105. For example, the reflector 112 may be formed within the plastic molded part by injection molding, and the lamp 110 may be assembled within the reflector 110. The plastic molded part may further include an aperture (not shown in Figure 1) configured to couple usable rays (e.g., a portion of the scattered light from the sample 108) to the spectrometer 104. For example, the aperture may have a shape and diameter configured to filter out a first portion of the scattered light (e.g., unusable sample information) and allow a second portion of the scattered light (e.g., usable sample information) to pass through. Furthermore, the aperture may be configured to filter out reflected light that does not contain sample information (e.g., light reflected from the optical window 106).

[0015] In some examples, the optical head 102 may optionally further include a focusing unit 115 (e.g., a focusing optical system). For example, the focusing optical system 115 may include one or more optical coupling elements 114, such as one or more lenses, for focusing available scattered light 130 from the sample 108 and coupling the available scattered light 130 to the input 125 of the spectrometer 104. In some examples, a microoptical system 116, such as one or more coupled micromirrors, may be placed at the input 125 to the spectrometer 104 to inject light into the spectrometer 104. The spectrometer 104 may be, for example, a Fourier transform infrared (FTIR) spectrometer. In some examples, the spectrometer 104 may include a Michelson interferometer or a Fabry-Perot interferometer. In the example shown in Figure 1, the spectrometer 104 includes a Michelson interferometer 118, which includes a beam splitter 120, a fixed mirror 122, and a movable mirror 124, the movable mirror may be coupled to, for example, an electrostatic actuator. The interferometer 118 is configured to generate an interferogram that can be detected by the detector 126. For example, the detector 126 may be an InGaAs photodetector extended to a wavelength of 2600 nm to cover the short-wavelength infrared (SWIR) range. The output of the detector 126 is processed to obtain the spectrum of the detected light, which can then be used to identify various parameters related to the sample 108.

[0016] In some examples, the spectrometer 104 can be realized as a micro-electromechanical system (MEMS) spectrometer. In this specification, the term MEMS refers to the integration of mechanical elements, sensors, actuators, and electronics onto a common substrate by microfabrication techniques. For example, microelectronics are typically manufactured using integrated circuit (IC) processes, while micromechanical components are manufactured using adaptable micromachining processes that selectively etch away portions of a silicon wafer or add new structural layers to form mechanical and electromechanical components. An example of a MEMS element is a micro-optical component with a dielectric or metallized surface that operates in reflective or refractive modes. Other examples of MEMS elements include actuators, detector grooves, and fiber grooves. In some examples, a MEMS spectrometer may include one or more micro-optical components (e.g., one or more reflectors or mirrors) that are movably controlled by a MEMS actuator. For example, a MEMS spectrometer can be fabricated on a silicon-on-insulator (SOI) substrate using a deep reactive ion etching (DRIE) process to create micro-optical components and other MEMS elements capable of processing a free-space light beam propagating parallel to the SOI substrate. For instance, a beam splitter 120, a fixed mirror 122, a movable mirror 124, and an electrostatic actuator (not shown for simplicity) can be fabricated on an SOI MEMS chip. The MEMS actuator can cause displacement of the movable mirror 124, enabling spectral resolutions of 16 nm and 8 nm at 1550 nm.

[0017] Figures 2A and 2B are diagrams showing an example of an optical head 200 of an optical device according to some embodiments. FIG. 2A is a top view of the optical head 200, and FIG. 2B is a bottom perspective view of the optical head 200. The optical head 200 includes a plastic molded part 202 formed, for example, by injection molding. A plurality of reflectors 204 are formed within the plastic molded part 202 and are coated with a metal coating to provide a high reflectivity exceeding 95% in the near-infrared range of 1000 nm to 3000 nm. The surface shape and curvature of the reflector 204 can be selected to achieve a desired illumination pattern (e.g., light spot size). In some examples, each of the plurality of reflectors 204 has an optical surface with a surface roughness of less than 10 nm. For example, the optical surface of the reflector 204 can be manufactured using a high-quality insert that provides the desired surface roughness. In some examples, the plurality of reflectors 204 may be elliptical reflectors with dimensions selected to generate a desired light spot size.

[0018] Furthermore, a plurality of lamp cups 206 (e.g., vertical cups) can be formed within the plastic molded part 202 inside the reflector 204. Each lamp cup 206 can be configured to receive a respective lamp 208. For example, each reflector 204 can include a vertical lamp cup 206, into which the lamp 208 can be inserted and fixed with an adhesive. Thus, each lamp 208 can be assembled into one of each of the reflectors 204. In the example shown in FIG. 2A, there are three lamps 208. However, the number of lamps 208 can be varied based on the desired light spot size. In some examples, the plastic material of the plastic molded part 202 is selected to withstand the high temperature (e.g., 2000°K to 3000°K) of the lamp 208. In some examples, each lamp 208 may be an incandescent lamp with a single filament.

[0019] An opening 210 is further formed within the plastic molded part 202. As described above, the opening 210 can have a position, shape, and diameter configured to filter light containing unusable sample information or light without sample information in order to maximize the coupling efficiency based on a desired light spot size. For example, the dimensions of the opening 210 can be selected to enhance the visibility of the spectrometer by restricting the acceptance angle of the direct current (DC) component of the interference signal while maintaining the acceptance angle of the alternating current (AC) component of the interference signal. In some examples, as shown in FIG. 2A, by removing the metal coating on each portion of the reflector 204 within the region 212 adjacent to and surrounding the opening 210, an error signal corresponding to light rays that do not contain spectral information about the sample can be reduced. In some examples, an area 212 without a metal coating can be obtained by controlling the metal deposition process on the plastic molded part 202, or by removing the metal coating within the region 212, or by removing the region 212 from the reflector 204.

[0020] The optical head 200 can further include a frame 214 formed within the plastic molded part 202. The frame 214 is configured to receive an optical window 218, and a test sample (not shown) can be placed on the optical window. In some examples, the optical window 218 can be attached to the frame 214 with epoxy. Further, as shown in FIG. 2B, the optical head 200 can further include a plurality of positioning pins 216 formed within the plastic molded part, and the opening 210 can be aligned with the input portion to the spectrometer.

[0021] Figures 3A and 3B show an optical device 300, including the optical head 200 shown in Figures 2A and 2B, relating to several embodiments. Figure 3A is a top perspective view of the optical device 300, and Figure 3B is a side view of the optical device 300. The optical head 200 includes a plastic molded part 302 with a plurality of reflectors 304 formed inside, as shown in Figure 2A. Furthermore, the optical head 200 further includes a plurality of lamps 306, each assembled in one of the plurality of reflectors 304. An optical window 308 is positioned on the optical head 200 to cover the plurality of reflectors 304 and the corresponding plurality of lamps 306. Furthermore, an aperture 310 in the plastic molded part 302 is aligned with the input to the spectrometer 312 in order to allow usable scattered light from a sample (not shown) on the optical window 308 to pass to the spectrometer 312. The optical head 200 and the spectrometer 312 can be assembled on a substrate 314 (for example, a printed circuit board (PCB)), and positioning pins on the optical head 200 (shown in Figure 2B) can be configured to align the aperture 310 with the input to the spectrometer 312 during assembly onto the substrate 314.

[0022] Figures 4A and 4B show another example of an optical head 400 of an optical device according to several embodiments. Figure 4A is a top view of the optical head 400, and Figure 4B is a side view of the various components of the optical head 400. The optical head 400 includes a plastic molded part 402 formed, for example, by injection molding. Multiple reflectors 404 are formed within the plastic molded part 402 and coated with a metal coating to provide high reflectivity. The surface shape and curvature of the reflectors 404 can be selected to obtain a desired illumination pattern (e.g., light spot size). In some examples, each of the multiple reflectors 404 has an optical surface with a surface roughness of less than 10 nm. For example, the optical surface of the reflector 404 can be manufactured using a high-quality insert that provides the desired surface roughness. In some examples, the multiple reflectors 404 may be elliptical reflectors of dimensions selected to yield a desired light spot size.

[0023] Furthermore, multiple lamp cups 406 (e.g., vertical cups) may be formed within the plastic molded part 402 inside the reflector 404. Each lamp cup 406 may be configured to receive its own lamp (not specifically shown in Figure 4A or Figure 4B). For example, each reflector 404 may include a vertical lamp cup 406 into which a lamp can be inserted and secured with adhesive. In this example, the lamp axis can be aligned with the mechanical axis of the reflector 404. In the example shown in Figures 4A and 4B, there are seven lamps, each assembled in one of the reflectors 404. However, the number of lamps can be varied based on the desired light spot size. In some examples, each lamp may be an incandescent lamp containing a double filament within the same glass envelope. In some examples, the two filaments are arranged so that the elliptical focus is centered between them in order to reduce the alignment sensitivity for lamp placement within the reflector 404. In some examples, the lamp glass includes a lens at the tip to collect the input light from the lamp and direct that input light towards the sample. In some examples, the position of the reflector 404 is selected to produce a target illumination spot (e.g., a large light spot size of 3 mm to 20 mm) on the sample with a target uniform intensity profile and low peak intensity values ​​(e.g., below a threshold peak intensity value) in order to prevent the sample from overheating.

[0024] An aperture 408 is further formed within the plastic molded part 402. The aperture 408 may have a position, shape, and diameter configured to filter out light containing or not containing sample information in order to maximize coupling efficiency based on a desired light spot size, as described above. The optical head 400 may further include a frame 214 formed within the plastic molded part 402. The frame 412 is configured to receive an optical window 410, on which a sample under test (not shown) can be placed. In some examples, the optical window 410 can be attached to the frame 214 by epoxy resin. For example, the optical window 410 can be fixed with an adhesive that can provide sealing above an IP65 rating. Although not shown in Figure 4A or Figure 4B, the optical head 400 may further include an optical coupling element (e.g., a lens) for collecting scattered light from the sample and coupling the scattered light to the input of the spectrometer.

[0025] Figure 5 shows an example of an optical device 500, including an optical head 400 as shown in Figures 4A and 4B, relating to several embodiments. The optical head 400 includes a plastic molded part 502 with a plurality of reflectors 504 formed inside, as shown in Figures 4A and 4B. Furthermore, the optical head 400 further includes a plurality of lamps 506 (e.g., seven lamps), each lamp being assembled in one of the plurality of reflectors 504. An optical window 510 is positioned on the optical head 400 to cover the plurality of reflectors 504 and the corresponding plurality of lamps 506. Furthermore, the plastic molded part 502 further includes an optical coupling element (e.g., a concave lens) 512 and an aperture 508 aligned to the input to the spectrometer 514, in order to allow usable scattered light from a sample (not shown) on the optical window 510 to pass into the spectrometer 514. In some examples, the focal length of the concave lens 512 can be selected to increase the acceptance angle of the spectrometer 514.

[0026] The optical head 400 and spectrometer 514 can be assembled on a substrate 516 (e.g., a printed circuit board (PCB)). Positioning pins 518 extending from the optical head 400 may be configured to align the aperture 508 to the input to the spectrometer 514 during assembly on the substrate 516. Furthermore, a heat sink 520 can be coupled to the plastic molded part 502, and metal pins 522 can be coupled to the heat sink, thereby providing heat dissipation from the electrical components of the optical head 400 and spectrometer, as well as mechanical assembly.

[0027] Figure 6 shows another example of an optical device 600, including an optical head 400 as shown in Figures 4A and 4B, relating to several embodiments. The optical head 400 includes a plastic molded part 602 with a plurality of reflectors 604 formed inside, as shown in Figures 4A and 4B. Furthermore, the optical head 400 further includes a plurality of lamps 606 (e.g., seven lamps), each lamp being assembled in one of the plurality of reflectors 604. An optical window 610 is positioned on the optical head 400 to cover the plurality of reflectors 604 and the corresponding plurality of lamps 606. Furthermore, the plastic molded part 602 further includes an optical coupling element (e.g., a concave lens) 612 and an aperture 608 aligned to the input to the spectrometer 614, in order to allow usable scattered light from a sample (not shown) on the optical window 610 to pass into the spectrometer 614. In some examples, the focal length of the concave lens 612 can be selected to increase the receiving angle of the spectrometer 614.

[0028] In the example shown in Figure 6, a plastic molded part 602 is assembled within a metal housing 618 to increase heat dissipation to the surroundings. Furthermore, the metal housing 618 may include fins 620 configured as a heat sink. By attaching an additional plastic molded part 622 to the metal housing 618, the flow of heat to the spectrometer can be blocked (or minimized). Additionally, an additional plastic molded part 622 can be attached to the spectrometer 614 to provide airtightness to the spectrometer 614.

[0029] The additional plastic molded part 622 and the spectrometer 614 can be assembled on a substrate 616 (e.g., a printed circuit board (PCB)). The additional plastic molded part 622 may further include a positioning pin 624 configured to align the aperture 608 with the input to the spectrometer 614 during assembly onto the substrate 616. A metal pin 626 can be coupled to a heat sink 620, thereby providing heat dissipation from the optical head 400 and the electrical components of the spectrometer, as well as mechanical assembly.

[0030] Figures 7A to 7C show examples of light filtering by an aperture 708 of an optical head according to several embodiments. As described herein, the aperture 708 is configured to limit unwanted rays coupled to the spectrometer. Unwanted rays can be classified into two main categories. Referring to Figure 7A, the first group includes rays 710 that are directly reflected from the optical window 700 (e.g., from the outer surface 702 or inner surface 704 of the optical window 700). This reflected light 710 does not contain sample information.

[0031] Referring to Figure 7B, the second group includes rays 712 scattered from the sample 706 on the optical window 700 but containing no usable sample information. For example, in a Fourier transform spectrometer, there is a DC portion and an AC portion of the interference signal (e.g., generated by a Michelson interferometer). The DC portion saturates the detector, limits the dynamic range of the spectrometer, and increases noise. The presence of this second group of unwanted rays 712 is due to the sensitivity of the generated interference to the polarization, angle, and relative position of the interfering rays.

[0032] Therefore, as shown in Figures 7A and 7B, the aperture 708 can be configured to filter both unwanted reflected rays 710 and rays 712 that do not contribute to the AC portion. Furthermore, as shown in Figure 7C, the aperture 708 can be further configured to allow rays 714 that contribute to the AC portion of the interference signal to pass through. In this way, the aperture 708 is configured to filter out a first portion 712 of the scattered light containing unusable sample information (e.g., the DC component of the scattered light) and to allow out a second portion 714 of the scattered light containing usable sample information (e.g., the AC component of the scattered light). In addition, the aperture 708 is configured to also filter out reflected light 710 that is directly reflected from the optical window 700.

[0033] In some cases, aperture 708 can increase the spectrometer's visibility by 2-3 times. The aperture shape and diameter can be selected to allow desired rays 714 to pass through while removing unwanted rays 710, 712. For example, the aperture shape may be a simple circle, but it can also be a complex shape to precisely remove unwanted rays and minimize the impact on the useful AC portion. Accurate modeling of the spectrometer's coupling and the sample's scattering profiles can be used to select the aperture design (e.g., shape and diameter). Furthermore, the position of aperture 708 relative to the sample 706 and an optional coupling lens can be considered. For example, the presence of this aperture 708 imposes a minimum distance between the sample 706 and the lens (not shown) so that different rays can be separated before spatial filtering. The aperture design can also take into account the spectrometer's acceptance angles (e.g., the acceptance angles for the useful AC portion and the DC portion). In some cases, the DC acceptance angle may be larger.

[0034] Figures 8A and 8B show examples of optical windows 800 of an optical device according to several embodiments. The optical window 800 includes an outer surface 802 on which a sample to be tested (not shown) can be placed, and an inner surface 804 opposite the outer surface 802. The optical window 800 allows light from the optical head of the optical device to pass through to the sample, and further allows scattered light from the sample to return to the optical head.

[0035] To enable the optical device to measure various types of samples with diverse mechanical and chemical properties (e.g., grains, feed, soil, rocks, etc.), the optical window 800 can have sufficient hardness (e.g., a hardness higher than the threshold hardness) to remain scratch-free even against highly abrasive samples while maintaining a high-quality optical interface. Furthermore, the optical window 800 can be designed with high transparency to increase the power supplied to the sample from the illumination unit, thereby maintaining the signal-to-noise ratio of the spectrometer and minimizing the lamp power as much as possible, thus maintaining the overall electrical efficiency of the optical device.

[0036] However, the highly transparent optical window 800 may produce reflections (e.g., reflections from the inner surface 804 or outer surface 802) that could adversely affect the performance of the spectrometer. These reflections may generate error signals in the spectrometer's detector. In certain applications, these error signals can be corrected in signal processing after data acquisition. However, these reflections may be partially dependent on the refractive index contrast between the window 800 and the sample, which may vary depending on the type of sample. This refractive index dependence may hinder the effective removal of error signals by signal processing correction techniques. Furthermore, absorption of light reflections by various components of the housing, fixtures, and system may cause various components to heat up, leading to thermal expansion and displacement of some optical components, or increasing noise in the electronic components of the spectrometer's electrical circuitry, which can adversely affect the device's performance.

[0037] Therefore, as shown in Figures 8A and 8B, an anti-reflective coating 806 can be added to the optical window 800 to reduce unwanted reflections. The anti-reflective coating 806 can provide high transmittance over the operating wavelength range of the spectrometer. In some examples, as shown in Figure 8A, the anti-reflective coating 806 can be applied to one side of the optical window 800 (e.g., the inner surface 804). In other examples, as shown in Figure 8B, anti-reflective coatings 806a and 806b can be applied to both sides of the optical window 800 (e.g., the inner surface 804 and the outer surface 802). Double-sided anti-reflective coating significantly reduces reflections from the window interface. However, anti-reflective coatings may not be hard enough to withstand scratching of the sample. Therefore, as shown in Figure 8A, applying the anti-reflective coating 806 to only the inner surface 804 may be a good compromise between unwanted reflections and scratch resistance.

[0038] Figures 9A to 9C show examples of spectrometer spot sizes in several embodiments. Referring to Figure 9C, the spectrometer 902 can be considered optically as an aperture 908 having a specific area and acceptance angle θ. The acceptance angle θ represents the angle of the head of the cone of light optically coupled from the illuminated spot 906 (e.g., 906c) on the sample to the spectrometer 902. For example, light scattered from the sample is optically coupled from the illuminated spot 906c toward the spectrometer 902. The throughput of the spectrometer 902 shown in Figure 9C can be written as follows: TIFF0007881198000001.tif16170

[0039] Scattered light from a sample typically spreads over a wide range of angles. If there is no lens between the sample and the spectrometer, the spot size (spot diameter 906c) observed by the spectrometer 901 is proportional to the distance d between the sample interface and the spectrometer aperture 908 and the tangent of the acceptance angle θ. If the distance d is large compared to the diameter of the aperture 908, and the focused spot area of ​​the illuminated spot 906c is much larger than the area of ​​the aperture 908, the effective area observed by the spectrometer (e.g., field of view) is approximated by the following relationship: TIFF0007881198000002.tif16170

[0040] MEMS-based spectrometers or other types of miniature spectrometers typically have limitations on aperture area and acceptance angle, sometimes less than 10 degrees. Spectral measurements of heterogeneous materials may not be suitable for such limited apertures. For this reason, as shown in Figures 9A and 9B, a focusing optical system 904 (e.g., an optical coupling element) can be used to transform the field of view of the spectrometer 902 to match the required field of view on the sample. This field of view depends on the application and can range from less than a few millimeters to tens of millimeters for large granular samples (such as plant seeds or soil for agricultural applications). Usually, for small field of view areas, the aperture 908 of the original spectrometer is sufficient to achieve the required averaging. However, as the field of view area increases, the design of the coupling optical system becomes more complex.

[0041] Due to the limitations of optical throughput, increasing the spot area means reducing the angular range of coupled rays from each point on the sample, as shown in Figures 9A and 9B. The focused spot area 906a shown in Figure 9A is smaller than the focused spot 906b shown in Figure 9B, which means that the focused spot angle α1 is larger than α2 in order to maintain a constant throughput. Therefore, in order to maintain an appropriate level of illumination intensity on the sample, the total power radiated from the lamp may increase to cover a larger spot area. This implies a trade-off between spot size, lamp power, and total power coupled to the instrument. Since the total power coupled affects the SNR, assuming the total radiated power from the lamp is the same, there is a trade-off between spot size and SNR.

[0042] In some examples, the coupling optical system 904 can be effectively modeled as a single concave lens. The concave lens effectively changes the acceptance angle θ so that more inclined rays are coupled and focused at the spectrometer aperture 908, as shown in Figures 9A and 9B. The focal length of the concave lens is determined by the distance d between the spectrometer aperture 908 and the sample, the diameter of the illumination spot 906a / 906b, and the acceptance angle θ of the spectrometer 902. The longer the allowable distance between the sample and the spectrometer, the greater the focal length. In most portable spectrometers, the overall size is a critical factor. For this reason, a shorter focal length can be used to obtain the required spot area. In some examples, the required focal length cannot be achieved with the focal lengths available with a single concave lens. For this reason, the coupling optical system 904 can include multiple optical coupling elements (e.g., multiple lenses) to effectively achieve the required short focal length.

[0043] Figure 10 shows an example of an optical coupling element 1004 of an optical head according to several embodiments. In the example shown in Figure 10, the optical coupling element 1004 includes a concave lens introduced between the optical window 1002 and the spectrometer aperture 1006. The spot radius of the illumination spot without the concave lens for a limited spectrometer aperture can be written as follows: TIFF0007881198000003.tif16170 Here, θ' is the input angle of the spectrometer. The actual spot radius may be larger, but if R'>u (where u represents the input aperture diameter of the spectrometer), equation 3 is a good approximation. Assuming a thin lens approximation, the following equation can be used to define the relationships between various parameters. TIFF0007881198000004.tif37170

[0044] Equation 7 shows that the spot radius increases when θ > θ', which can be achieved with a negative focal length system. By using equations 4-7 above, design curves with various parameters can be generated. For example, if the acceptance angle of the spectrometer is 6.6° and the total distance between the spectrometer aperture 1006 and the sample (optical window 1002) is 50 mm, the spot radius without a lens system is given by the following equation. TIFF0007881198000005.tif16170 In some examples, the minimum spot diameter is 15 mm, taking into account manufacturing variations and assembly tolerances of various system components. In this example, the spot radius in Equation 8 is smaller than the minimum spot diameter. Therefore, by including a lens system (e.g., concave lens 1004), the spot diameter can be increased to the desired optical spot size.

[0045] Figure 11 shows design curves for spot sizes depending on the distance between the sample and the optical coupling element in several embodiments. These design curves are shown for various spot sizes with varying lens positions from the sample, while keeping the total distance constant at 50 mm for various focal lengths. As shown, by increasing the curvature of the lens, a larger spot radius can be achieved within the same dimensions. The resulting set of curves provides a potential range of focal length options. However, conventional biconvex lenses have the following constraints on their lens diameter: TIFF0007881198000006.tif16170

[0046] Therefore, the maximum collision point of light rays on the lens can be written as follows: TIFF0007881198000007.tif16170

[0047] This allows for the elimination of several points on the generated set of curves. This condition can be relaxed if an aspherical lens is used. However, the same constraint may still apply even with the new relaxed limit. For practical reasons related to illumination, d should be kept higher than the threshold to avoid interference with the illumination path. The curves shown in Figure 11 can be generated for both the expected minimum and expected maximum acceptance angles of the spectrometer, which can more accurately represent the variability between units in manufacturing.

[0048] The above calculations serve as initial design points for the focusing optical system. In designing the illumination unit, the optical power coupled to the spectrometer (e.g., provided by the spectrometer manufacturer) to achieve a specific signal-to-noise ratio can be converted into a minimum level of intensity on the sample surface. In some examples, this conversion can be utilized for the initial computational design of the focusing optical system. This intensity can then be integrated over the irradiated sample area to calculate the total amount of optical power required for the system.

[0049] In one example, the total optical power on the sample required to achieve the desired signal-to-noise ratio for a given spectrometer is approximately equal to 2 watts. As a reasonable initial assumption, 60% of the optical power emitted by the lamp is focused and directed to the sample surface. In some examples, a filament lamp can be used to provide a broad spectral range beyond 1000 nm. In this example, filament radiation can be approximated by blackbody radiation. Therefore, not all optical power is emitted within the spectrometer's operating wavelength range. For example, the spectrometer can operate in the NIR region from 1300 nm to 2600 nm. The blackbody spectrum can be integrated to calculate the effective portion of the radiation within the operating range (referred to herein as spectral efficiency). This can be performed for various blackbody temperatures in the range of 2000°K to 3000°K, assuming emissivity is equal to 1 for simplicity. The calculated values ​​are summarized in the table below. TIFF0007881198000008.tif56170

[0050] As shown in Table 1, spectral efficiency improves with decreasing temperature, but at the cost of reduced radiance within the operating spectral band. For example, a midpoint with a spectral efficiency of 44.7% can be selected, and a tungsten filament lamp with the corresponding midpoint temperature can be used. Electrical-to-optical efficiency can be defined as the ratio of the total light power radiated across the entire wavelength range to the total power injected into the lamp. Assuming an electrical-to-optical efficiency of 80%, the total power required to achieve the desired signal-to-noise ratio can be calculated as follows: TIFF0007881198000009.tif45170

[0051] In addition to selecting the lamp's operating temperature, the overall structural size can be reduced by designing the lamp's external dimensions to be small enough to fit within a small reflector. Furthermore, a small lens can be used to couple light from the front of the lamp to the sample, while the sides are covered with a reflector.

[0052] In one example, the optical device shown in Figures 4-6 can use seven lamps rated at 1.5 watts each. Each lamp contains two filaments assembled within a glass envelope. The filaments can operate at a temperature of 2450°K.

[0053] After selecting the number of lamps and their power ratings, the optical head can be designed to maximize the filament-to-sample coupling. For example, an estimate of the minimum distance from the sample to which the lamps and reflectors are positioned can be calculated.

[0054] Figure 12 shows exemplary configurations of various components of an optical head 1200 of an optical device that can be used to estimate minimum distance according to several embodiments. The optical head 1200 includes a plurality of reflectors 1202 (one of which is shown for convenience), a plurality of corresponding lamps 1204 (one of which is shown for convenience), and an optical coupling element (e.g., a concave lens) 1220. Each lamp 1204 includes two filaments (e.g., a rear filament 1206 and a front filament 1208) within a glass envelope 1214. Holes can be drilled in the reflectors 1202 to secure the glass envelope 1214 and for electrical connections to the lamps 1204. In some examples, each lamp 1204 may further include a small lens 1205 at its tip to collect input light from the lamp 1204 and guide the input light to a sample on the optical window 1212 of the optical device.

[0055] The free space 1218 between the sample (e.g., the optical window 1212 on which the sample is placed) and the optical coupling element 1220 can be defined within the optical head 1200 so as not to block scattered light from the sample. This space 1218 can be calculated using knowledge of edge rays 1222 that fall within the lens-receiving range emitted from the sample surface. Next, assuming a target spot region 1216 (e.g., target spot size) of 10 mm to 15 mm, and assuming the axis 1232 of the reflector 1202 is tilted at 45° with respect to the optical axis 1224 of the concave lens 1220, the minimum distance can be estimated to be 5 mm from basic geometric calculations. The calculated minimum distance provides a target for the reflector 1202 and lens 1205 around the filaments 1206 and 1208 to refocus the light at that distance.

[0056] Based on the minimum distance, the curvature of each reflector 1202 can be designed to refocus the filament light emitted in all directions relative to the sample. In the example shown in Figure 12, the reflector 1202 has an elliptical curvature. The elliptical reflector 1202 focuses all the light emitted from one focal point (e.g., elliptical focus 1210a) to the other focal point (e.g., elliptical focus 1210b). Thus, the lamp 1204 can be positioned on one side of the focal point 1210a (e.g., the elliptical focus 1210a is between the double filaments 1206 and 1208), as shown in Figure 12, and the sample point can be positioned at the other focal point 1210b. In some examples, the elliptical linear eccentricity 1230 of the reflector 1202 can be at least 5 mm. Furthermore, the minor axis diameter 1228 of the reflector 1202 is at least the same size as the diameter of the lamp 1204. For example, if the glass envelope 1205 of the lamp 1204 has a diameter of 3.5 mm, then the minor axis diameter 1228 is at least 3.5 mm. However, in order to produce an effective focusing effect on the reflector 1204, there should be sufficient space around the lamp 1204. For this reason, the minor axis diameter may be constrained to be at least twice the diameter of the lamp glass (e.g., 7 mm).

[0057] The optical axis 1224 can further correspond to the central axis of the optical device aligned with the aperture and the input to the spectrometer. To achieve a large illumination spot 1216 (e.g., 3 mm to 20 mm), a reflector 1202 with a lamp 1204 can be positioned at a certain position (e.g., shift 1226) and angle θ from the central axis 1224 to generate free space 1218 and achieve the target illumination spot 1216 on the sample at the estimated minimum distance from the sample. Furthermore, each of multiple reflectors 1202 can be further oriented relative to the central axis 1224 to achieve a target uniform intensity profile of the illumination spot 1216 on the sample with a peak intensity value below a threshold (e.g., to prevent overheating of the sample). Figure 12 shows a single lamp 1204 with a reflector 1202, but it should be understood that other lamps can be positioned in the same location for a sample distributed circumferentially.

[0058] The uniformity on the sample can be calculated by adding multiple annular detectors with consecutive radii and calculating the intensity of each ring. Therefore, uniformity is defined as the standard deviation of all ring intensities divided by the average intensity of all rings, as follows: TIFF0007881198000010.tif17170

[0059] The peak intensity value of the illumination spot indicates low sample heating. This design is chosen to achieve low peak intensity values ​​and uniformity at a specific illumination power on the sample.

[0060] Figures 13A to 13C illustrate exemplary processes for measuring the spot size of a spectrometer in an optical device according to several embodiments. In the examples shown in Figures 13A to 13C, the optical device includes an illumination unit, which includes a plurality of lamps 1302 and a corresponding plurality of reflectors 1304, each reflector surrounding one of the plurality of lamps 1302. The optical device further includes an optical window 1306 on which a sample may be placed, a focusing optical system 1308 (e.g., one or more optical coupling elements such as lenses), and a spectrometer 1310. The spot size of the spectrometer 1310 is measured, for example, using a knife-edge technique, with a highly scattering reference material 1312 (e.g., polytetrafluoroethylene (PTFE)) mounted on a moving stage controlled by a positioner 1314. The spectrometer 1310 may then be configured to measure a target spot diameter based on the power detected by the spectrometer 1310 relative to the lateral position of the moving reference sample 1312 on the optical window 1306. For example, initially, the knife edge is positioned away from the optical window 1306, and therefore the reference sample 1312 reflects no power to the spectrometer aperture. Then, as shown in Figures 13A-13C, the positioner 1314 can move the knife edge in constant linear steps until the reference sample 1312 covers the entire illumination spot and the power saturates, capturing power at each step, thereby obtaining cumulative power versus displacement. By differentiating the cumulative power, an intensity profile can be obtained. Next, the spot diameter can be calculated by fitting the intensity profile to a Gaussian distribution (or by other types of fitting) and defining the spot size as the beam diameter containing 90% of the reflected power. It should be understood that the spot diameter can also be calculated using other methods.

[0061] The following is an overview of the embodiments of this disclosure.

[0062] Example 1: An optical device comprising: an optical head comprising a plastic molded part, an aperture formed in the plastic molded part, a plurality of reflectors formed around the aperture in the plastic molded part, and a plurality of lamps, each of the plurality of lamps being assembled in each of the plurality of reflectors; an optical window disposed on the optical head, the optical window configured to receive a sample, allow input light from the plurality of lamps to pass through to the sample, and allow scattered light scattered from the sample to pass through to the aperture, the aperture having a shape and diameter configured to filter a first portion of the scattered light and allow a second portion of the scattered light to pass through, the first portion of the scattered light containing unusable sample information; and a spectrometer configured to receive the second portion of the scattered light at an input unit and obtain the spectrum of the sample based on the second portion of the scattered light.

[0063] Example 2: An optical device as described in Example 1, characterized in that the unusable sample information includes a direct current (DC) component of scattered light, and the aperture is configured to limit the first spectrometer acceptance angle of the DC component of scattered light and maintain a second spectrometer acceptance angle of the alternating current (AC) component of scattered light.

[0064] Example 3: An optical device according to Example 1 or 2, characterized in that the aperture is further configured to filter reflected light directly reflected from the optical window.

[0065] Example 4: An optical device according to any one of Examples 1 to 3, characterized in that the plastic molded part includes a metal coating on a plurality of reflectors.

[0066] Example 5: An optical device as described in Example 4, characterized in that the metal coating on each portion adjacent to the aperture of a plurality of reflectors is removed.

[0067] Example 6: An optical device according to any one of Examples 1 to 5, characterized in that the optical window has an anti-reflective coating on its inner surface.

[0068] Example 7: An optical device according to Example 6, wherein the optical window further has an additional anti-reflective coating on its outer surface, and a sample is placed on its outer surface.

[0069] Example 8: An optical device according to any of Examples 1 to 7, characterized in that each of the multiple reflectors has an optical surface with a surface roughness of less than 10 nm.

[0070] Example 9: An optical device according to any of Examples 1 to 8, characterized in that the optical head further comprises a positioning pin configured to align the aperture with the input section to the spectrometer.

[0071] Example 10: An optical device according to any of Examples 1 to 9, characterized in that the optical head has a central axis aligned with the aperture and the input section to the spectrometer, and each of the plurality of reflectors is directed at an angle and position with respect to the central axis such that it generates an illumination spot on the sample that includes the target spot diameter.

[0072] Example 11: An optical device as described in Example 10, characterized in that each of the multiple reflectors is further directed with respect to the central axis to achieve a target uniform intensity profile of the illumination spot on the sample with a peak intensity value below a threshold.

[0073] Example 12: An optical device according to Example 10 or 11, characterized in that the spectrometer is configured to measure the target spot diameter based on the power detected by the spectrometer with respect to the lateral position of a moving reference sample on an optical window.

[0074] Example 13: An optical device according to any of Examples 1 to 12, characterized in that each of the plurality of reflectors includes an elliptical reflector.

[0075] Example 14: An optical device according to Example 13, characterized in that each of the plurality of lamps includes a glass envelope and a double filament, and the double filament is arranged within the glass envelope such that an elliptical focus is located between the double filaments.

[0076] Example 15: An optical device in which the glass envelope comprises a lens that focuses the input light and guides the input light to the sample, in the optical device described in Example 14.

[0077] Example 16: An optical device according to any of Examples 13 to 15, characterized in that the lamp axis of each of the multiple lamps is aligned with the mechanical axis of each of the multiple reflectors.

[0078] Example 17: An optical device according to any of Examples 1 to 16, further comprising a heat sink bonded to a plastic molded part and metal pins bonded to the heat sink for heat dissipation.

[0079] Example 18: An optical device, characterized in that it further includes a metal housing for housing a plastic molded part, as described in Example 17.

[0080] Example 19: An optical device according to Example 18, characterized in that the metal housing includes a plurality of fins configured as a heat sink.

[0081] Example 20: An optical device according to Example 18 or 19, further comprising a metal housing and an additional plastic molded part attached to a spectrometer, wherein the additional plastic molded part includes a positioning pin configured to align the aperture with the input portion to the spectrometer.

[0082] Example 21: An optical device according to any of Examples 1 to 20, further comprising an optical coupling element configured to couple a second portion of scattered light to the input to a spectrometer via an aperture.

[0083] Example 22: An optical device according to Example 21, characterized in that the optical coupling element includes a concave lens.

[0084] Example 23: An optical device according to Example 21 or 22, characterized in that the focal length of the optical coupling element is selected to increase the acceptance angle of the spectrometer.

[0085] Example 24: An optical device according to any of Examples 1 to 23, characterized in that a plastic molded part includes a plurality of reflectors, a plurality of lamps and a frame surrounding an aperture, and an optical window is fixed to the frame.

[0086] Example 25: An optical device according to any of Examples 1 to 24, characterized in that the plurality of lamps include three lamps or seven lamps.

[0087] Within this disclosure, the word “exemplary” is used to mean “serving as an example, embodiment, or specific example.” An implementation or aspect described herein as “exemplary” should not necessarily be construed as being preferable or advantageous to other aspects of this disclosure. Similarly, the term “aspect” does not require that all aspects of this disclosure include the features, advantages, or modes of operation discussed. The term “combined” is used herein to refer to a direct or indirect combination between two objects. For example, if object A is in physical contact with object B, and object B is in contact with object C, objects A and C may still be considered combined with each other, even if they are not in direct physical contact with each other. For example, object 1 may be combined with object 2 even if object 1 is not in direct physical contact with object 2. The terms “circuit” and “circuitry” are used broadly and are intended to include both hardware implementations of electrical devices and conductors and software implementations of information and instructions, where hardware implementations, when connected and configured, enable the performance of the functions described herein, without being limited to the type of electronic circuit, and software implementations, when performed by a processor, enable the performance of the functions described herein.

[0088] One or more of the components, steps, features, and / or functions shown in Figures 1 to 13C may be rearranged and / or combined into a single component, step, feature, or function, or may be embodied in several components, steps, or functions. Additional elements, components, steps, and / or functions may be added without departing from the novel features disclosed herein. Apparatus, devices, and / or components shown in Figures 1 to 13C may be configured to perform one or more of the methods, features, or steps described herein. Novel algorithms described herein may be efficiently implemented in software and / or embedded in hardware.

[0089] It should be understood that the specific order or hierarchy of steps in the disclosed method is illustrative of an exemplary process. It should be understood that the specific order or hierarchy of steps in the method may be rearranged based on design orientation. The appended claims for the method present elements of various steps in a sample order and are not intended to be limited to the specific order or hierarchy presented unless otherwise specified herein.

[0090] The foregoing description is provided to enable those skilled in the art to implement the various embodiments described herein. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may also apply to other embodiments. Accordingly, the claims are not intended to be limited to the embodiments shown herein, but should be given the entire scope consistent with the language of the claims, and references to elements in the singular are not intended to mean “one” unless specifically stated so, but rather to mean “one or more.” Unless specifically stated, the term “several” means one or more. The phrase “at least one of” a list of items refers to any combination of those items, including a single member. For example, “at least one of a, b or c” is intended to cover: a, b, c and: a and b and: a and c and: b and c and: a, b and c. All structural and functional equivalents to elements of the various embodiments described herein, known or to those skilled in the art, are expressly incorporated herein by reference and are intended to be included in the claims. Furthermore, nothing disclosed herein is intended to be made available to the public, whether such disclosure is expressly contained in the claims. No element of a claim should be construed under Section 112(f) of the United States Patent Act unless it is expressly described using the phrase “means for,” or, in the case of a method claim, using the phrase “step for.”

Claims

1. An optical device, An optical head comprising a plastic molded part, an opening formed in the plastic molded part, a plurality of reflectors formed around the opening in the plastic molded part, and a plurality of lamps, wherein each of the plurality of lamps is assembled in one of the plurality of reflectors, An optical window disposed on the optical head, wherein the optical window is configured to receive a sample, allow input light from the plurality of lamps to pass through the sample, and allow scattered light scattered from the sample to pass towards the aperture, and the aperture has a shape and diameter configured to filter a first portion of the scattered light and allow a second portion of the scattered light to pass through, wherein the first portion of the scattered light contains unusable sample information, The system includes a spectrometer configured to receive a second portion of the scattered light at an input unit and to obtain a spectrum of the sample based on the second portion of the scattered light, An optical device characterized in that the unusable sample information includes the direct current (DC) component of scattered light and stray light originating from reflections from the interface of the optical window, the aperture is configured to limit a first spectrometer acceptance angle for the DC component of the scattered light and maintain a second spectrometer acceptance angle for the alternating current (AC) component of the scattered light, the optical head has a central axis aligned with the aperture and the input to the spectrometer, each of the plurality of reflectors is directed at an angle and position with respect to the central axis such that it generates an illumination spot on the sample including a target spot diameter, and the spectrometer is configured to measure the target spot diameter based on the power detected by the spectrometer with respect to the lateral position of a moving reference sample on the optical window.

2. In the optical device described in claim 1, The optical device is characterized in that the aperture is further configured to filter reflected light that is directly reflected from the optical window.

3. An optical device according to claim 1, characterized in that the plastic molded part includes a metal coating on the plurality of reflectors.

4. In the optical device described in claim 3, An optical device characterized in that the metal coating on each portion of the plurality of reflectors adjacent to the aperture is removed.

5. In the optical device described in claim 1, The optical device is characterized in that the optical window has an anti-reflective coating applied to its inner surface.

6. In the optical device according to claim 5, The optical device is characterized in that the optical window further has an additional anti-reflective coating on its outer surface, and a sample is placed on the outer surface.

7. In the optical device described in claim 1, An optical device characterized in that each of the plurality of reflectors has an optical surface having a surface roughness of less than 10 nm.

8. In the optical device described in claim 1, The optical device is characterized in that the optical head further comprises a positioning pin configured to align the aperture with the input section to the spectrometer.

9. In the optical device described in claim 1, An optical device characterized in that each of the plurality of reflectors is further directed with respect to the central axis to achieve a target uniform intensity profile of the illumination spot on the sample with a peak intensity value below a threshold.

10. In the optical device described in claim 1, An optical device characterized in that each of the plurality of reflectors includes an elliptical reflector.

11. In the optical device according to claim 10, An optical device characterized in that each of the plurality of lamps includes a glass envelope and a double filament, and the double filament is arranged within the glass envelope such that an elliptical focus is located between the double filaments.

12. In the optical device according to claim 11, The optical device is characterized in that the glass envelope comprises a lens that collects the input light and guides the input light to the sample.

13. In the optical device according to claim 10, An optical device characterized in that the lamp axis of each of the plurality of lamps is aligned with the mechanical axis of each of the plurality of reflectors.

14. In the optical device described in claim 1, A heat sink attached to the aforementioned plastic molded part, An optical device further comprising metal pins coupled to the heat sink for heat dissipation.

15. In the optical device according to claim 14, An optical device further comprising a metal housing for housing the aforementioned plastic molded part.

16. In the optical device according to claim 15, An optical device characterized in that the metal housing includes a plurality of fins configured as a heat sink.

17. In the optical device according to claim 15, An optical device further comprising the metal housing and an additional plastic molded part attached to the spectrometer, wherein the additional plastic molded part includes a positioning pin configured to align the aperture with the input portion to the spectrometer.

18. In the optical device described in claim 1, The optical device further comprises an optical coupling element configured to couple a second portion of the scattered light to the input to the spectrometer via the aperture.

19. In the optical device according to claim 18, An optical device characterized in that the optical coupling element includes a concave lens.

20. In the optical device according to claim 18, An optical device characterized in that the focal length of the optical coupling element is selected to increase the acceptance angle of the spectrometer.

21. In the optical device described in claim 1, An optical device characterized in that the plastic molded part includes the plurality of reflectors, the plurality of lamps, and a frame surrounding the opening, and the optical window is fixed to the frame.

22. In the optical device described in claim 1, An optical device characterized in that the plurality of lamps include three lamps or seven lamps.

Images