Apparatus and method for Raman spectroscopy

Abstract

The present invention relates to an apparatus and method for Raman spectroscopy, and in particular to an apparatus and method for high-resolution Raman spectroscopy comprising a tunable monochromatic laser source that is spectrally modulated by a modulation signal for exciting a sample, and a lock-in device for improving the signal-to-noise ratio of a sample Raman signal occurring within the spectral filter width of a narrowband spectral filter element in an associated measurement signal. The device for Raman spectroscopy according to the present invention is mod1 The present invention relates to a spectrally tunable laser source (10) modulatable by a first modulation signal (S), a spectral filter element (20), a detector (30) for measuring the intensity of the excitation radiation (L1) of the laser source (10) scattered by the sample (P) and filtered by the spectral filter element (20), a means for tuning the laser source (50), and a first modulation signal (S mod1 ) as a reference signal to determine the spectral filter width Δν Filter The first modulating signal (S mod1 and a lock-in device (40) configured to filter the Raman signal (R) of the sample (P) modulated by the Raman filter (R) from the measurement signal (I).

Description

[Technical Field]

[0001] The present invention relates to an apparatus and method for Raman spectroscopy, and in particular to an apparatus and method for high-resolution Raman spectroscopy comprising a spectrally tunable monochromatic laser source that is spectrally modulated by a modulation signal for exciting a sample, and a lock-in device for improving the signal-to-noise ratio of a Raman signal of the sample that occurs within the spectral filter width of a narrowband spectral filter element in an associated measurement signal. [Background technology]

[0002] Raman spectroscopy is increasingly being used in industrial processes and environmental measurement techniques due to its suitability for in situ and online analysis. However, one drawback is that some samples, as a result of their fluorescence and / or scattering properties, produce spectra that are impaired by high background, especially when working without elaborate sample preparation and / or with compact instruments, with measurement times of less than one second.

[0003] In Raman spectroscopy, the sample under investigation is typically illuminated with excitation radiation at a fixed, but spectrally nearly freely selectable, excitation wavelength. The excitation radiation inelastically scattered by the sample is then collected from the sample position using an appropriate spectroscopy setup and spectrally analyzed. Depending on the specific material properties of the sample, individual Raman lines appear in the recorded spectrum, which have precisely defined spectral intervals (customarily called wavenumber intervals) from the excitation wavelength of the excitation radiation that are characteristic of the sample under investigation.

[0004] In addition to high spectral resolution, the spectrometer used to record Raman spectra must be sufficiently sensitive to light to record the scattering spectrum. Typically, such spectrometers have a high-resolution grating as the wavelength-selective element and a multichannel detector with adequately low noise, such as an electronically or liquid nitrogen-cooled CCD camera, for detection. Such spectrometers are often expensive and not particularly suitable for building small, compact, and robust spectroscopy setups.

[0005] Another drawback of conventional spectroscopy setups is their relatively low sensitivity. This is because narrowband filtering by wavelength-selective elements results in low intensities in each wavelength range, and therefore the measured Raman signal has a low signal-to-noise ratio (SNR). The SNR can be increased by increasing the intensity of the excitation radiation or extending the respective integration time, but such measures are subject to severe limitations depending on the use case. On the one hand, excessive excitation power can affect or even destroy the sample, and on the other hand, particularly short measurement times are required for monitoring chemical processes or detecting harmful substances.

[0006] EP 3309538 A1 and EP 3660474 A1 also disclose spectroscopic setups equipped with a tunable monochromatic excitation light source, in which specific Raman signals from a sample are selectively detected through spectrally narrowband filter elements. Here, the SNR can be improved by specifically exciting a sample with excitation radiation from a narrowband wavelength range specifically suited to the sample, without special adaptation of the spectroscopic setup. The single-channel detector used for signal acquisition enables rapid signal acquisition, and detection sensitivity can be significantly improved compared to conventional setups. However, for more reliable, more accurate, and faster Raman spectroscopy of samples, even under suboptimal excitation conditions, the SNR of the acquired Raman signal must be further improved for broader application. Summary of the Invention [Problem to be solved by the invention]

[0007] DISCLOSURE OF THE INVENTION

[0008] It is therefore an object of the present invention to provide an apparatus and method for high-resolution Raman spectroscopy that allows an increase in SNR compared to the prior art, thereby reducing the required integration time while at the same time improving the sensitivity of the spectroscopy setup.

[0009] According to the invention, these objects are achieved by the features of claims 1, 9 and 10. Advantageous configurations of the invention are set out in the dependent claims. The features set out individually in the claims can be combined with one another in a technically meaningful way and can be supplemented by explanatory facts from the description and / or details from the drawings, which show further variant embodiments of the invention. [Brief explanation of the drawings]

[0010] DETAILED DESCRIPTION OF THE INVENTION

[0011] A first aspect of the present invention relates to a spectrally tunable laser source configured to emit a monochromatic first form of excitation radiation at a first wavelength λ1 from a first wavelength range Δλ1 for exciting a sample, and a filter wavelength ν Filter and the spectral filter width Δν Filter and a spectral filter element having a first wavelength range Δλ1 and a spectral filter width Δν Filter associated with non-overlapping spectral ranges; a detector for measuring the intensity of the excitation radiation filtered by the spectral filter element as a measurement signal; and tuning means for the laser light source, the tuning means being adapted to tune the first wavelength λ1 of the laser light source to a frequency f mod1tuning means for modulating the spectral filter width Δν of the spectral filter element from the measurement signal using the first modulating signal as a reference signal; Filter and a lock-in device configured to filter a Raman signal of the sample generated within the spectral filter element and modulated with a first modulation signal. Thus, using the first modulation signal as a reference signal, the lock-in device adjusts the spectral filter width Δ of the spectral filter element. νFilter The signal-to-noise ratio of a measured signal of a Raman signal of the sample generated within the sample and modulated with the first modulation signal can be improved.

[0012] In Raman spectroscopy, a sample is excited with excitation radiation and the occurrence of at least one specific Raman line is spectroscopically investigated. In particular, for the purposes of the present invention, this is taken to mean the spectroscopic investigation of a sample at at least one preselected Raman line of the sample. However, it is also possible to simply investigate the presence of a corresponding Raman line in an unknown sample.

[0013] Monochromatic excitation radiation is understood to mean radiation with a small spectral width at a central wavelength determined as the excitation wavelength. Such excitation radiation can typically be emitted by a diode laser or laser diode operating in single mode. The spectral width should be selected to match the spectral resolution of the measurement system and the spectral width of the Raman line under investigation. A central wavelength of approximately 785 nm with a spectral half-width ("full width at half maximum", FWHM) of less than 1 nm is particularly preferred here.

[0014] The laser light sources are spectrally tunable over a first wavelength range Δλ1, and each emission wavelength (i.e., the first wavelength λ1) of the laser light sources varies at a frequency f within the first wavelength range Δλ1. mod1The wavelength range Δλ is modulated with a first modulation signal of λ. Tuning is taken to mean detuning of a particular radiation wavelength λ within the associated wavelength range Δλ. This can be, for example, continuous or discontinuous tuning of a particular radiation wavelength λ within the associated wavelength range Δλ (e.g., quasi-continuous tuning with at least one spectral step change range). Binary tuning between wavelength λ and a relatively detuned wavelength λ+δλ within the wavelength range Δλ associated with wavelength λ is also referred to as switchover ("digital" modulation). Typical modulation widths are about 5 nm to 10 nm. The accessible wavelength range Δλ can be correspondingly wider. The maximum frequency f at which each radiation wavelength of the excitation radiation can be modulated is mod The preferred modulation frequency f depends heavily on the modulation characteristics of the modulator, the laser source, and the possible readout speed of the associated detector. mod is about 0.01 Hz, more preferably 0.1 Hz, more preferably 1 Hz, more preferably 10 Hz, more preferably 100 Hz, and even more preferably 1 kHz. At an assumed radiation wavelength of 785 nm, the wavelength range Δλ available for modulation of 10 nm (modulation width) is about 160 cm -1 corresponds to the wavenumber range of

[0015] The excitation radiation scattered by the sample is filtered at a specific filter wavelength ν Filter (where the symbol ν denotes a wave number corresponding to a wavelength commonly used in Raman spectroscopy) is spectrally filtered by a spectral filter element. The spectral filter element may preferably be a passive filter element, in particular a dichroic filter, a Bragg filter (e.g., Bragg grating, VBG, FBG), or a Fabry-Perot filter. Likewise, it is preferable to use a diffraction grating, an etalon, or a Mach-Zehnder interferometer. Passive means that the filter characteristics of the filter element are not actively modified in order to record the Raman spectrum, in particular the filter wavelength ν of the spectral filter element. Filter This means that is time invariant.

[0016] Spectral filtering is the process of filtering wavelengths, specifically, Filter Monochromatic radiation of ν is transmitted through the filter element with maximum intensity, and the filter wavelength ν Filter The term "filtering" is intended to mean filtering in which a spectral range adjacent to the filter wavelength v is suppressed or blocked. The spectral filter element may be a suitably configured reflective filter element. Filter is the center wavelength of the passband (also called the transmission range) of the filter element. For a symmetric bandpass filter, this is obtained from the spectral position of the center of the bandpass filter. Alternatively, the center wavelength of a filter element can be determined based on the transmission behavior in the passband.

[0017] The center wavelength can be conveniently determined based on the center of the spectral range, with the filter element having a relative transmittance of at least 0.9 compared to the maximum transmittance in the passband. This definition is particularly suitable for determining the center wavelength of a spectral filter element having asymmetric filter range edges. The width of the passband of the spectral filter element (i.e., the width Δν of the spectral filter) is Filter ) can also be defined based on its transmission behavior. The passband of a spectral filter element can be defined as a continuous spectral range in which the relative transmittance is preferably at least 0.95 compared to the maximum transmittance in the passband. Continuous spectral ranges in which the relative transmittance is at least 0.7, at least 0.8, at least 0.9, or at least 0.99 are even more preferred. The cutoff range of a filter element can also be correspondingly defined based on the transmission characteristics of the spectral filter element within this cutoff range. A spectral filter element is defined to have a filter wavelength ν for this wavelength. Filter Wavelengths having a relative transmittance of less than 0.3, less than 0.2, less than 0.1, less than 0.5, or less than 0.01 compared to the maximum transmittance of the spectral filter element in the passband can be considered to be blocked.

[0018] The spectral filter element is preferably spectrally narrowband. Spectrally narrowband means that the spectral filter width Δν Filter This means that the wavelength or wavenumber range of the device is limited to a certain spectral range. Particularly preferred passband widths (FWHM) are less than 10 nm, less than 5 nm, less than 1 nm, and less than 0.1 nm. Depending on the wavelength range, this corresponds to a frequency bandwidth from the lower THz range up to the MHz range.

[0019] First wavelength range Δλ1 and spectral filter width Δν Filter are related to non-overlapping spectral ranges. This means that excitation light having a first wavelength λ1 from a first wavelength range Δλ1 and directly scattered by the sample is filtered by the spectral filter element. Therefore, excitation light can be transmitted or reflected by the spectral filter element only if a corresponding frequency shift has previously occurred in the excitation light due to inelastic scattering (e.g., due to a Stokes or anti-Stokes shift occurring within the sample). Direct or elastically scattered excitation light (e.g., due to Rayleigh or Mie scattering on the sample) is filtered by the spectral filter element, which means that the SNR cannot be reduced as a result.

[0020] The detector is preferably a single-channel detector. This can be either an individual single-channel detector or a multi-channel detector that can be read out individually as a corresponding single-channel detector. This has the advantage that particularly inexpensive, compact, and robust detector devices can be used. It is not necessary to use a high-resolution, low-noise, and highly sensitive CCD camera. If a multi-channel detector with individual channels operates as a single-channel detector, several channels of the multi-channel detector can also be combined to form individual single-channel detectors.

[0021] The apparatus according to the present invention comprises a lock-in device, via which the first modulated signal is used as a reference signal to determine the spectral filter width Δν of the spectral filter element. Filter The signal-to-noise ratio of the Raman signal of the sample generated within the sample and modulated with the first modulation signal can be enhanced in the detected measurement signal by corresponding frequency-selective electronic filtering of the Raman signal. mod1 The first modulation signal is modulated by an associated means for tuning the laser source, allowing the lock-in device to be set to the corresponding reference signal, thereby improving the SNR. As a result, additional noise components caused by ambient light, residual scattered light, and other factors that interfere with spectroscopy can be effectively suppressed in the measurement signal, and therefore, despite detection by a single-channel detector, the Raman signal can be selectively obtained as a corresponding low-noise evaluation signal. Lock-in techniques and lock-in devices are well known in the prior art and are commonly used to filter specific frequency-modulated signals from the measurement signal based on the corresponding reference signal.

[0022] The lock-in device may in particular be a lock-in amplifier, in which the filtered signal is further amplified. However, the amplification factor may take any real value. In particular, the amplification factor of the lock-in amplifier may be 0, 1 or -1. An amplification factor of 0 means that the signal filtered by the lock-in amplifier is completely attenuated.

[0023] The main idea of ​​the present invention is therefore to use a lock-in technique to significantly increase the SNR compared to prior art techniques, enabling shorter integration times and increased sensitivity compared to comparable spectroscopy setups. The Raman signal can be acquired and evaluated virtually noise-free via individual single-channel detectors. The device according to the present invention can therefore be manufactured very compactly, simply, and inexpensively, without moving mechanical parts. Thanks to the simple optical path, the excitation power can be varied without additional measures depending on the sample being investigated.

[0024] The spectrally tunable laser source is preferably configured to emit a monochromatic second form of excitation radiation at a second wavelength λ2 from a second wavelength range Δλ2 for exciting the sample, the second wavelength λ2 of the laser source being tuned by a tuning means of the laser source at a frequency f mod2 (within an associated second wavelength range Δλ2), and the lock-in device determines from the measurement signal the spectral filter width Δν of the spectral filter element using the second modulated signal as a reference signal. Filter The lock-in device is configured to filter the Raman signal of the sample generated within the spectral filter element and modulated with the second modulation signal. Thus, the lock-in device uses the second modulation signal to adjust the spectral filter width Δν of the spectral filter element. Filter The signal-to-noise ratio of a measured signal of a Raman signal of the sample generated within the sample and modulated with the first modulation signal can be improved.

[0025] The spectrally tunable laser source is preferably configured to emit excitation radiation in the form of at least one further monochromatic wavelength λ3 from a further wavelength range Δλ3 for exciting the sample, the at least one further wavelength λ3 of the laser source being tuned by a tuning means of the laser source at a frequency f mod3(within at least one further associated wavelength range Δλ3), and the lock-in device determines from the measurement signal the spectral filter width Δν of the spectral filter element using the at least one further modulated signal as a reference signal. Filter The lock-in device is configured to filter a Raman signal of the sample generated within the spectral filter element and modulated with at least one further modulation signal. Thus, the lock-in device uses the at least one further modulation signal to adjust the spectral filter width Δν of the spectral filter element. Filter The signal-to-noise ratio of the measured signal of the Raman signal of the sample generated within the sample and modulated with at least one further modulation signal can be improved.

[0026] The different forms of excitation radiation are preferably emitted simultaneously, but each form of excitation radiation may be emitted with a time delay. The forms of excitation radiation can be provided, for example, by using multiple laser diodes emitting at different emission wavelengths in a laser light source. The different forms of excitation radiation at different excitation wavelengths can also be generated by a single laser diode with a variable emission wavelength or by a corresponding spectrally tunable diode laser. In addition to providing discrete, spaced emission wavelengths (e.g., 10 nm or 20 nm apart), it is also possible to appropriately select each emission wavelength from the wide available spectral range of a laser light source.

[0027] It is preferable to use laser diodes that can excite different modes, so that a larger, at least discretely achievable, wavelength range can be achieved, for example with a spacing of a few tens of nanometers. Direct frequency modulated laser diodes, where the wavelength can be changed by intrinsic diode parameters, for example via temperature or current, are also preferable.

[0028] For example, a "dual-wavelength" or "multi-wavelength" laser such as a Y-branch dual-wavelength DBR diode laser (e.g., Maiwald et al., "Dual-Wavelength Y-Branch Distributed Bragg Reflector Diode Laser at 785 Nanometers for Shifted Excitation Raman Difference Spectroscopy", Appl. Spectrosc. 69, 1144-1151 (2015)) may be preferably used. Furthermore, it is preferred that the laser source is a corresponding narrow-band diode laser that is spectrally tunable over a wide range. This may be, for example, an ECDL system or a spectrally tunable diode-pumped solid-state laser. Correspondingly tunable dye lasers or fiber lasers are also particularly suitable.

[0029] The wavelength ranges associated with at least two forms of excitation radiation, i.e., all wavelength ranges associated with each form of excitation radiation, do not overlap with each other. This means that, also with respect to modulation, the forms of excitation radiation do not have a spectral overlap, and therefore, each tunable form of excitation radiation can be uniquely associated with an individual wavelength range. The designated filter wavelength ν Filter In combination with the spectral filter element having , this means that the wavenumber ranges that are spectrally separated by the modulation also do not overlap with one another.

[0030] Preferably, for a given sample under investigation, at least two forms of excitation radiation are applied to the spectral filter element with a spectral filter width Δν Filter, which are selected so that different Raman signals occur within the spectral filter element. This embodiment is particularly applicable to samples with different compositions (e.g., different molecules, chemical groups, etc.). In these cases, different forms of excitation radiation can be set to measure different Raman lines of individual components of the composition. It is then possible to determine, for example, the mixing ratio of the compositions based on the intensity ratio of the measured Raman signals. However, the spectral filter width Δν of the spectral filter element Filter The different Raman signals generated within may be formed by different Raman lines of individual sample components. By evaluating multiple Raman lines from individual sample components, the reliability of sample determination can be improved.

[0031] Preferably, at least two forms of excitation radiation are modulated at a uniform frequency and phase angle via respective modulation signals. Such an embodiment has the advantage that, for example, two different Raman lines (i.e., belonging to different wavenumber intervals) of two signals filtered from the two forms of excitation radiation via a spectral filter element are acquired as a sum signal by a lock-in device at a common modulation frequency. The signal level measured by the lock-in device is a superposition of two different Raman signals from individual sample components. Compared to acquiring one specific Raman signal, measuring multiple Raman signals in parallel can further significantly improve the SNR.

[0032] In particular, the corresponding high maximum signal level (e.g., above a certain threshold) can be used as the basis for inferring the simultaneous occurrence of different Raman lines from specific sample components (or specific sample materials). Such additive Raman spectroscopy can achieve high sensitivity and reliability of the spectroscopic setup, especially in the specific determination of individual samples, with the shortest integration times.

[0033] The generated Raman signal is preferably based on both the Stokes shift and the anti-Stokes shift. The phrase "generated Raman signal" refers to the spectral filter width Δν of the spectral filter element.Filter The term refers to the actual presence in the measured signal of a Raman signal from the sample generated within the sample and modulated with a first modulation signal. This term therefore refers to the wavelength of the excitation radiation modulated in the relevant wavelength range and the filter wavelength v of the spectral filter element used. Filter The signed spectral interval (wavenumber interval) between

[0034] The Stokes shift involves an energy transfer from the photon of excitation radiation to the scattering sample. After the scattering process, the molecules of the sample are in a higher energy level than before, and the scattered photons have lower energy and frequency than the excitation photons. The anti-Stokes shift involves an energy transfer from the sample to the photon of excitation radiation. After the excitation process, the molecules of the sample are in a lower energy level than before, and the scattered photons have higher energy and frequency than the excitation photons.

[0035] In a preferred embodiment, both the Stokes shift and the anti-Stokes shift are acquired as Raman signals. The intensity ratio of the Stokes shift and the anti-Stokes shift of each Raman signal can be used to specifically measure the temperature of the sample. Therefore, for spatially extensive samples containing different components, it is also possible to perform highly position-specific and material-specific temperature measurements of individual components of the sample's composition. State-specific temperature measurements are also possible, for example, temperature measurements of single rotational and vibrational states of molecules in thermal non-equilibrium.

[0036] The device according to the invention preferably comprises at least one display device for displaying the measurement signal filtered by the lock-in device. The display device may preferably be a simple analog or digital pointer element or a binary display element (e.g., optical signal above a certain threshold). Furthermore, the display device may preferably be an analog or digital time plotter for depicting the Raman signal as a time profile in a corresponding diagram. Preferably, each different Raman signal is displayed on an associated display device.

[0037] The described embodiments can be advantageously combined in whole or in part.

[0038] A further aspect of the invention is a method for Raman spectroscopy using an apparatus according to the invention, comprising: determining the wavelengths (λ1, λ2, λ3) of at least one form of excitation radiation (L1, L2, L3) and the filter wavelength v of a spectral filter element; Filter The spectral interval between is the wavenumber interval Δν ~ In Raman spectroscopy, a sample is excited with excitation radiation and the occurrence of at least one specific Raman line is investigated spectroscopically. Thus, to perform Raman spectroscopy of a given sample using the device according to the invention, the wavelength λ of the monochromatic excitation radiation modulated in the relevant wavelength range Δλ and the filter wavelength v of the spectral filter element are selected. Filter At least one spectral interval between the wavenumber interval Δν ~ Therefore, if no corresponding Raman signal occurs during spectroscopy of a particular sample, it can be concluded that at least the corresponding sample pre-determined for testing is not present.

[0039] A further aspect of the present invention relates to the use of the method according to the present invention for measuring the temperature or the mixing ratio of a sample. The temperature of the sample can be measured, in particular, via the intensity ratio of the Stokes shift and anti-Stokes shift of the respective Raman signals. The mixing ratio of samples with different compositions (e.g., different molecules, chemical groups, etc.) can be measured by the intensity ratio of the individual Raman lines of the different components. Therefore, the method according to the present invention can also be used to record the time profile of the mixing ratio (e.g., for in situ monitoring of chemical reactions in reactors). The mixing ratio of a sample can be used, for example, to determine the degree of saturation of a solution or the degree of polymerization in a polymerizable monomer solution.

[0040] In addition, further preferred configurations of the method according to the invention are directly apparent from the features described in the specification with respect to the device according to the invention.

[0041] Further preferred configurations of the invention are revealed by the features set forth in the respective dependent claims.

[0042] The different embodiments of the invention described in this application can be advantageously combined with one another, unless otherwise stated.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present invention and technical background will be described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not intended to be limited to the exemplary embodiments described. In particular, unless expressly stated otherwise, it is also possible to extract sub-aspects of the subject matter described in the drawings and combine them with other elements and insights of this specification.

[0045] FIG. 1 shows a schematic diagram of a first embodiment of an apparatus according to the invention for Raman spectroscopy with associated spectra.

[0046] FIG. 2 shows a schematic diagram of a second embodiment of an apparatus according to the invention for Raman spectroscopy with associated spectra.

[0047] FIG. 3 shows a schematic diagram of a third embodiment of an apparatus according to the invention for Raman spectroscopy with associated spectra.

[0048] FIG. 4 shows an exemplary diagram of the spectrum of the third embodiment of the device according to the invention of FIG.

[0049] Detailed Description of the Drawings

[0050] 1 is a schematic diagram of a first embodiment of an apparatus according to the invention for Raman spectroscopy with an associated spectrum. The apparatus shown in Fig. 1 a) comprises a spectrally tunable laser source 10, which is configured to emit a monochromatic first form of excitation radiation L1 at a first wavelength λ1 from a first wavelength range Δλ1, for exciting a sample P; Filter and the spectral filter width Δν Filter a spectral filter element 20 having a first wavelength range Δλ1 and a spectral filter width Δν Filter a spectral filter element 20 associated with a non-overlapping spectral range; a detector 30 for measuring the intensity of the first excitation radiation L1′ scattered by the sample P (i.e., the first form of excitation radiation L1′ scattered by the sample) and filtered by the spectral filter element 20 (i.e., the excitation radiation L1″ scattered by the sample and filtered by the spectral filter element) as a measurement signal I; tuning means for the laser source 50, which is configured to tune the first wavelength λ1 of the laser source 10 at a frequency f mod1 The first modulated signal S mod1 (within a first wavelength range Δλ1 associated therewith) means for modulating the measurement signal I; mod1 as a reference signal, the spectral filter width Δν of the spectral filter element 20 Filter The first modulated signal S mod1 and a lock-in device 40 configured to filter the Raman signal R of the sample P modulated at the modulation frequency (f mod1 ) is provided with a display device 60 for displaying the measurement signal I filtered by the lock-in device 40. The filtering is performed by filtering the first modulation signal S mod1 The signal-to-noise ratio of the measured signal l of the Raman signal R of the sample P modulated by the

[0051] The spectra shown in figures b) and c) show the spectral relationship during modulation. These spectra are obtained by measuring the excitation radiation (ν L1 ) and individual Raman lines ν1 L1 ~ν4L1 (The symbol ν is the wavenumber related symbol conventionally used in Raman spectroscopy to denote wavelength and was chosen for ease of expression) and the respective wavenumber interval Δν ~ Excitation radiation (ν L1 ) is plotted against the filter wavelength ν Filter where the spectral filter width Δν Filter Also shown is the filter range of the spectral filter element 20, which has the excitation radiation (ν L1 ) and the filter wavelength ν of the spectral filter element 20. Filter The wavenumber interval between -1 Figure b) shows the excitation radiation (ν L1 ) is shown. Figure c) shows the ratio of the excitation radiation v L1 The excitation radiation (ν L1 +δν1). The entire Raman spectrum is also spectrally shifted by the same amount δν1, so in the example shown, the fourth Raman line ν4 L1 +δν1 is the spectral filter width Δν of the spectral filter element 20 Filter Therefore, the Raman line ν4 L1 is ν L1 and ν4 L1 A simple modulation of the excitation radiation during +δν 1 allows detection with the aid of the spectral filter element 20 .

[0052] 2 shows a schematic diagram of a first embodiment of an apparatus according to the invention for Raman spectroscopy with an associated spectrum. The apparatus shown in FIG. 2a) substantially corresponds to the embodiment shown in FIG. 1a). The reference symbols and their respective assignment to the individual features of the apparatus are therefore applied accordingly. In contrast to the embodiment shown in FIG. 1a), the spectrally tunable laser source 10 is set to emit a monochromatic second form of excitation radiation L2 at a second wavelength λ2 from a second wavelength range Δλ2 for exciting the sample P, the second wavelength λ2 of the laser source 10 being tuned by the tuning means of the laser source 50 at a frequency f mod2 The second modulation signal S mod2 (within a second associated wavelength range Δλ2), and the lock-in device 40 derives from the measurement signal I a second modulated signal S mod2 as a reference signal to determine the spectral filter width Δν of the spectral filter element 20. Filter The second modulated signal S mod2 The illustrated device is further configured to filter the Raman signal R of the sample P modulated at two modulation frequencies (f mod1 , f mod2 ) are provided with two display devices 60, 60' for displaying the measurement signal I filtered by the lock-in device 40.

[0053] The spectra shown in figures b) and c) show the spectral relationships during modulation of the individual forms of excitation radiation, which correspond to the ratios shown in figures 1b) and c). In this example, the first form of excitation radiation ν L1 and the second form of excitation radiation ν L2 The wavenumber interval between -1 Therefore, as shown in Figure b), two Raman lines ν4 L1 and v3 L2 With the help of the spectral filter element 20, by spectral tuning (e.g., detuning, tuning, or switching over) each form of excitation radiation (ν L1 , ν L2 ) correspondingly.

[0054] 3 shows a schematic diagram of a third embodiment of the apparatus according to the invention for Raman spectroscopy with an associated spectrum. The apparatus shown in FIG. 3 a) substantially corresponds to the embodiment shown in FIG. 2 a). The reference symbols and their respective assignment to the individual features of the apparatus are therefore applied accordingly. In contrast to the embodiment shown in FIG. 2 a), the spectrally tunable laser source 10 is configured to emit at least one further monochromatic form of excitation radiation L3 at a further wavelength λ3 from a further wavelength range Δλ3 in order to excite the sample P, the at least one further wavelength λ3 of the laser source 10 being tuned by tuning means of the laser source 50 at a frequency f mod3 at least one further modulated signal S mod3 (within at least one further relevant wavelength range Δλ3), and the lock-in device 40 derives from the measurement signal I at least one further modulation signal S mod3 as a reference signal to determine the spectral filter width Δν of the spectral filter element 20. Filter and at least one further modulated signal S mod3 The illustrated device is further configured to filter the Raman signal R of the sample P modulated at three modulation frequencies (f mod1 , f mod2 , f mod3 ) at least two display devices 60, 60' for displaying the measurement signal I filtered by the lock-in device 40.

[0055] 4 shows an exemplary diagram of the spectrum of a third embodiment of the device according to the invention of FIG. 3. In this embodiment, four monochromatic forms of excitation radiation (ν L1 , ν L2 , ν L3 , ν L4 ) is the spectral filter width Δν of the spectral filter element 20 Filter Different Raman lines (ν1 L4 , ν2 L3 , ν3 L2 , ν4 L1) is selected to occur. Corresponding to the illustrations of FIGS. 1b) and 1c), FIG. 4a) shows the spectral filter width Δν Filter Spectrally superimposed Raman lines (ν1) for the unmodulated form of pump radiation at a specific output wavelength λ located within L4 , ν2 L3 , ν3 L2 , ν4 L1 ) while b) shows the excitation radiation at output wavelength λ (ν L1 , ν L2 , ν L3 , ν L4 ) the corrected ratio in the case of a corresponding modulation of the form of the shifted Raman line ν1 L4 +δν4, ν2 L3 +δν3, ν3 L2 +δν2, ν4 L1 +δν1, and the shifted form of excitation radiation (ν L1 +δν1,ν L2 +δν2,ν L3 +δν3,ν L4 +δν3). For this purpose, we use the monochromatic form of excitation radiation (ν L1 , ν L2 , ν L3 , ν L4 ) is the corresponding modulated signal S mod1 , S mod2 , S mod3 , S mod4 and the associated Raman signals can be displayed on displays 60, 60', respectively. [Explanation of symbols]

[0056] 10. Spectrally tunable laser sources 20 Spectral Filter Elements 30 detectors 40 Lock-in Device 50. Laser source tuning means 60, 60' display unit L1 First form of excitation radiation L1' Excitation radiation scattered by the sample L1" Excitation radiation scattered by the sample and filtered by the spectral filter element L2 Second form of excitation radiation L2': the second form of excitation radiation scattered by the sample L2" is the second form of excitation radiation scattered by the sample and filtered by the spectral filter element L3 Further forms of excitation radiation L3' Further forms of excitation radiation scattered by the sample L3" further forms of excitation radiation scattered by the sample and filtered by the spectral filter element P sample I Measurement signal R Raman signal S mod1 First Modulation Signal S mod2 Second Modulation Signal S mod3 Third Modulation Signal

Claims

1. 1. An apparatus for Raman spectroscopy, comprising: A first wavelength range Δλ for exciting the sample (P) １ The first wavelength λ from １ of the monochromatic first form of excitation radiation (L １ a spectrally tunable laser source (10) configured to emit The filter wavelength is ν Ｆｉｌｔｅｒ and the spectral filter width Δν Ｆｉｌｔｅｒ a spectral filter element (20) having the first wavelength range Δλ １ and the spectral filter width Δν Ｆｉｌｔｅｒ associated with non-overlapping spectral ranges; The excitation radiation (L) scattered by the sample (P) and filtered by the spectral filter element (20) １ a detector (30) for measuring the intensity of the light reflected from the incident light as a measurement signal (I); The first wavelength λ of the laser light source (10) １ is the frequency f ｍｏｄ１ The first modulated signal (S ｍｏｄ１ a tuning means (50) for said laser light source, modulated by a From the measurement signal (I), the first modulated signal (S ｍｏｄ１ ) as a reference signal to determine the spectral filter width Δν of the spectral filter element (20). Ｆｉｌｔｅｒ and the first modulated signal (S ｍｏｄ１ a lock-in device (40) configured to filter the Raman signal (R) of said sample (P) modulated with the Raman signal (R).

2. 2. The apparatus according to claim 1, wherein the spectrally tunable laser source (10) is configured to emit a second wavelength range Δλ for exciting the sample (P). ２ The second wavelength λ ２ Monochromatic second form of excitation radiation (L ２ ), and the second wavelength λ of the laser light source (10) is set to emit ２ is tuned to a frequency f by the tuning means (50) of the laser light source. ｍｏｄ２ The second modulated signal (S ｍｏｄ２ ) and the lock-in device (40) derives the second modulated signal (S) from the measurement signal (I). ｍｏｄ２ ) as a reference signal to determine the spectral filter width Δν of the spectral filter element (20). Ｆｉｌｔｅｒ and the second modulated signal (S ｍｏｄ２ ) modulated Raman signal (R) of said sample (P).

3. 3. The apparatus according to claim 2, wherein the spectrally tunable laser source (10) is configured to provide at least one further wavelength range Δλ for exciting the sample. ３ Further wavelengths λ from ３ Further monochromatic forms of excitation radiation (L ３ ), and the at least one further wavelength λ of the laser light source (10) ３ is tuned to a frequency f by the tuning means (50) of the laser light source. ｍｏｄ３ at least one further modulated signal (S ｍｏｄ３ ) and the lock-in device (40) derives from the measurement signal (I) the at least one further modulation signal (S ｍｏｄ３ ) as a reference signal to determine the spectral filter width Δν of the spectral filter element (20). Ｆｉｌｔｅｒ and said at least one further modulated signal (S ｍｏｄ３ ) modulated Raman signal (R) of the sample.

4. 4. The device according to claim 2 or 3, wherein the at least two forms of excitation radiation (L １ , L ２ , L ３ ) related to the wavelength range (Δλ １ , Δλ ２ , Δλ ３ ) do not overlap each other, device.

5. 5. An apparatus according to claim 2, wherein for a given sample (P) to be spectroscopically investigated, the excitation radiation (L １ , L ２ , L ３ ) form of the spectral filter element (20) Ｆｉｌｔｅｒ The device is selected so that different Raman signals (R) are generated within the device.

6. 6. The device according to claim 2, wherein the excitation radiation (L １ , L ２ , L ３ ) form of each of said modulated signals (S ｍｏｄ１ , S ｍｏｄ２ , S ｍｏｄ３ ) modulated at a uniform frequency and phase angle.

7. 7. The apparatus according to claim 2, wherein the Raman signal (R) generated is based on both the Stokes shift and the anti-Stokes shift.

8. The device according to any one of claims 1 to 7, further comprising at least one display device (60, 60') for displaying the measurement signal (I) filtered by the lock-in device (40).

9. A method for Raman spectroscopy using an apparatus according to any one of claims 1 to 8, comprising the step of: applying at least one form of excitation radiation (L １ , L ２ , L ３ ) wavelength (λ １ , λ ２ , λ ３ ) and the filter wavelength v of the spectral filter element (20) Filter The spectral interval between the Raman signals (R) of a given sample (P) is the wavenumber interval Δν ～ A method corresponding to.

10. 10. Use of the method according to claim 9 for measuring the temperature of a sample (P) or the mixing ratio of a sample (P).

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