Method for checking wavelength shift on a detector in a spectrometer

Abstract

This invention relates to a method for checking wavelength shifts on a detector in a spectrometer. A method for checking wavelength shifts on a detector (2) in a spectrometer (1), wherein the spectrometer (1) includes a sample unit (3) and a detector (2), wherein the sample unit (3) is configured to generate optical properties of a sample, wherein the detector (2) has multiple pixels and is configured to detect the generated light as a spectrum, wherein the method includes the steps of: creating a first wavelength association by associating wavelengths with pixels of the detector (2); acquiring a first spectrum of the sample, the first wavelength association being valid for the first spectrum; acquiring a second spectrum of the sample; determining a wavelength shift between the first and second spectra based on a comparison of the first and second spectra; and creating a second wavelength association, wherein wavelengths are associated with pixels in the second spectrum based on the determined wavelength shift.

Description

Technical Field

[0001] The present invention relates to a method for checking wavelength shifts on a detector in a spectrometer, wherein the spectrometer includes a sample unit and a detector, wherein the sample unit is configured to generate optical properties of a sample, particularly to excite the sample to emit light or to irradiate the sample with light passing through it, wherein the detector has multiple pixels and is configured to detect the generated light as a spectrum. Background Technology

[0002] In analysis, a spectrometer is used to analyze light emitted from a sample (or, in certain cases, a stimulated sample) or light transmitted through the sample. The term "light" specifically refers to electromagnetic radiation. The light being measured passes through various optical components such as lenses, filters, mirrors, and / or gratings before reaching a detector, which detects the light in the form of a spectrum.

[0003] Examples of spectrometers include absorption spectrometers and emission spectrometers. In the case of an absorption spectrometer, light transmitted through the sample falls onto a detector, and the sample's extinction rate, etc., is determined. An emission spectrometer examines the light emitted when the sample is stimulated, and for example, uses an echelle grating. An echelle grating is a diffraction grating with high diffraction efficiency for high diffraction orders. When combined with a second dispersive element (grating or prism), the echelle grating enables the generation of a two-dimensional diffraction order structure. In this way, particularly precise analysis of the sample is achieved.

[0004] To correlate the pixels of the detector with wavelengths, a reference measurement is performed. For example, a reference lamp with a known wavelength emits light onto the detector. Based on the position of the reference lamp's light on the detector, the pixels can then be correlated with wavelengths. Because the position of wavelengths on the detector can change over time (due to thermal drift and / or other reasons, such as pressure fluctuations in the spectrometer or vibrations in the motors used to move the optics of the spectrometer), this reference measurement is repeated periodically and, for example, redefined before each sample measurement. However, this requires additional measurements between sample measurements. Summary of the Invention

[0005] Therefore, the object of the present invention is to provide a method that makes it easy to check wavelength shift.

[0006] According to the present invention, this objective is achieved by the method defined herein.

[0007] According to the present invention, this objective is achieved by a method for checking wavelength shifts on a detector in a spectrometer, wherein the spectrometer includes a sample unit and a detector, wherein the sample unit is configured to generate optical properties of a sample, particularly to excite the sample to emit light or to irradiate the sample with light passing through it, wherein the detector has multiple pixels and is configured to detect the generated light as a spectrum, wherein the method includes the following steps: - Create the first wavelength association by associating the wavelength with the pixels of the detector. - The first spectrum of the acquired sample, the first wavelength correlation is effective for the first spectrum. - Collect the second spectrum of the sample. - The wavelength shift between the first and second spectra is determined by comparing the first and second spectra. - Create a second wavelength association, where wavelengths are associated with pixels in a second spectrum based on the determined wavelength offset.

[0008] According to the invention, a first wavelength correlation is provided and applied to a first spectrum. By comparing the first spectrum with a second spectrum, it is determined that a wavelength shift has been determined between the two spectra. This avoids reference measurements between the first and second spectra and allows for faster spectral analysis of the sample. In particular, the detector is configured to display the intensity of the generated light at each pixel. The spectrum thus formed then displays the light intensity for each pixel. In the context of this invention, intensity always refers to light intensity. The wavelength shift may occur horizontally, vertically, or laterally to the detector. Therefore, the wavelength shift can be determined as a two-dimensional vector. Using this two-dimensional vector, wavelengths can be shifted relative to pixels such that they correspond to a second wavelength correlation. In this case, the translation value in the two-dimensional vector can be smaller than the pixel size. The second spectrum is acquired particularly after the first spectrum. In a given situation, no drift may occur between the first and second spectra, resulting in a wavelength shift of zero and the second wavelength correlation corresponding to the first wavelength correlation.

[0009] The method of this invention is particularly applicable to absorption and emission spectrometers. It is especially advantageous for echelle spectrometers, particularly ICP-OES (inductively coupled plasma optical emission spectrometers) without temperature control. Drift in ICP-OES spectrometers is often addressed through temperature control (and thus heating or cooling) to minimize wavelength shift. Consequently, echelle spectrometers without such temperature control require numerous reference measurements. The method of this invention minimizes these. Similarly, the method of this invention can also be advantageously applied to atomic absorption spectrometers.

[0010] In one embodiment, the method includes the following steps: - Acquire a first spectrum of the sample, which includes multiple spectral structures, particularly emission structures, wherein at least one spectral structure is selected from the first spectrum as the test structure. - Acquire the second spectrum of the sample and locate the test structure in the second spectrum. - The wavelength shift between the first and second spectra is determined by comparing the test structures based on the first and second spectra. - Create a second wavelength association, where wavelengths are associated with pixels in a second spectrum based on the determined wavelength offset.

[0011] The spectral structure specifically corresponds to the characteristic wavelength of the sample. When the sample unit is implemented to excite the sample to emit light, the spectral structure is particularly the emission structure. Excitation of the sample can be performed, for example, by plasma. The emission structure has a positive light intensity and is visible as a bright region in the spectrum.

[0012] Alternatively, when the sample unit is implemented to illuminate the sample with light that has passed through it, the spectral structure can also be an absorption structure. Since an absorption structure is characterized by a reduction in the intensity of light initially incident on the sample, it is darker than the rest of the spectrum and is characterized by lower intensities. Therefore, in a given situation, the first and second spectra can be converted to extinction spectra before selecting or finding a test structure. Alternatively, a first and second inverse spectrum can be formed from the first and second spectra by taking the reciprocal of all intensities of the spectrum. In this way, the original absorption structure appears as a positive structure in the inverse or extinction spectrum, allowing for easier evaluation.

[0013] If more than two spectra of a sample are collected, all spectra can be collected before selecting a test structure. This ensures that the selected test structure can be well evaluated in each spectrum.

[0014] The selected test structure can be a spectral structural characteristic of the sample and therefore can be found in every spectrum of the sample. It is specifically assumed that the morphology of the test structure remains the same in each spectrum, and therefore does not change between the first and second spectra. Here, "morphology" refers both to the geometric arrangement of the test structure on the pixels and the intensity distribution of the test structure on the pixels. The test structure remains structurally unchanged, but its position in the spectrum changes only according to wavelength shifts. The detected intensity distribution may differ slightly between spectra only due to the discrete pixel grid. Typically, the total intensity (i.e., the sum of intensities) of the test structure on each pixel also does not change. However, this does not apply to transient spectral structures, which occur, for example, when measuring a specific sample, and in the case of transient spectral structures, the intensity may fluctuate due to irregular concentration distributions in the sample. The test structure selected in the first spectrum is searched for in the second spectrum. In this case, a first position of the test structure in the first spectrum and a second position of the test structure in the second spectrum can be determined. By comparing the test structure in the first and second spectra, wavelength shifts can be detected.

[0015] In one embodiment, the selected test structure is a spectral structure having a predetermined minimum area, a predetermined minimum signal-to-noise ratio, and / or a predetermined minimum intensity. To facilitate comparison of the test structures in the first and second spectra, conditions can be set for the selection of the test structure; for example, the test structure must have a predetermined minimum area, thus extending over a predetermined number of pixels. Furthermore, one condition could be that the test structure has a predetermined minimum signal-to-noise ratio, thus minimizing the signal-to-noise ratio. Another condition could be that the test structure has a predetermined minimum intensity, thus ensuring that the sum of the light intensities across all pixels extending from the test structure exceeds the predetermined minimum intensity.

[0016] In one embodiment, the comparison of the test structure in the first and second spectra is based on the determination of the intensity center of the test structure. The so-called "intensity center" is the center of the test structure; however, it is not determined based on mass distribution, but rather in a similar manner based on the intensity distribution of light on pixels. For this purpose, typical methods for determining the centroid can be used, where mass is replaced by light intensity and position by pixels. For example, pixels extending from the test structure are weighted individually by the intensity associated with each pixel. In this case, the pixel can also be divided into multiple sub-pixels, each weighted individually by its corresponding intensity. Based on the intensity distribution generated in this way, the intensity center can then be determined. In particular, with this embodiment, a wavelength shift value is obtained, which can be smaller than the pixel size.

[0017] In one embodiment, the wavelength shift corresponds to the difference in intensity centers of the test structure in the first and second spectra, specifically the vector difference. Since the test structures in the two spectra are structurally identical and only their positions in the spectra change with the wavelength shift, the wavelength shift can be determined based on the difference between the intensity centers of the test structures in the first and second spectra.

[0018] In one embodiment, the comparison of the test structure in the first and second spectra is based on fitting the test structure to a second- or higher-order function. This function can be a Gaussian function or a Lorentz function. The test structure can be fitted to this function, for example, according to a two-dimensional image on the detector. Alternatively, the pixels of the test structure along one axis of the detector can be summed (i.e., added together), and fitted in this one-dimensional representation. In this case, the expected value of the Gaussian function or the maximum value of the Lorentz function then corresponds to the intensity center of the test structure. In this case, it is assumed that the intensity distribution of the test structure is symmetrical. By comparing the expected or maximum values ​​of the test structure in the first and second spectra, the wavelength shift can be determined.

[0019] In one embodiment, the comparison of the test structure in the first and second spectra is based on the edge of the test structure. The edge of the test structure corresponds to a transition region of intensity from the background signal to the test structure and is characterized by a sharp increase in intensity, thus making it easily detectable. By selecting the edge and comparing its position in the first and second spectra, the wavelength shift can be determined.

[0020] In one embodiment, a test structure in a second spectrum is located based on a first position of the test structure in a first spectrum. To locate the selected test structure in the second spectrum, it is advantageous to determine the first position of the test structure in the first spectrum and locate the test structure in the second spectrum based on that first position. Due to the wavelength shift between the first and second spectra, the first position of the test structure differs from a second position of the test structure in the second spectrum. Typically, the test structure in the second spectrum is expected to be near the first position.

[0021] In one embodiment, locating the test structure in the second spectrum includes the following steps: - Determine the first position of the test structure in the first spectrum. - Locate the spectral structure in a predetermined region surrounding the first position within the second spectrum. - Compare the morphology of the test structure in the first spectrum with the morphology of the spectral structure found in the second spectrum. When the deviation between these two morphologies is within the tolerance range, the found spectral structure is determined to correspond to the test structure. The method is terminated when the deviation between these two forms exceeds the tolerance range.

[0022] The test structure in the second spectrum can be determined based on its first position in the first spectrum. In this case, the second position of the test structure in the second spectrum is expected to be within a predetermined region surrounding the first position. If the second position of the test structure extends beyond the predetermined region, it indicates a significant wavelength shift, making it impossible to determine the wavelength shift by comparing the first and second spectra. Instead, a new first wavelength correlation must be established, such as through a new reference measurement. Ideally, this reference measurement should allow for more precise wavelength correlation. Therefore, if no spectral structure is found within the predetermined region surrounding the first position, the method terminates here.

[0023] If a spectral structure can be determined within a predetermined region surrounding the first location, the morphology of the test structure in the first spectrum is compared with the morphology of the found spectral structure. Since it is assumed that the morphology of the test structure remains substantially unchanged, the found spectral structure can be considered to correspond to the test structure when the deviation of the morphology of the found spectral structure is within the tolerance range of the morphology of the test structure in the first spectrum. If the difference between the two morphologies exceeds the tolerance range, the determined spectral structure is not the test structure of the first spectrum, and the method terminates.

[0024] In one embodiment, multiple spectral structures in a first spectrum are selected as test structures, and these test structures are found in a second spectrum. The wavelength shift between the first and second spectra is determined based on a comparison of the test structures in the first and second spectra. Because multiple test structures are selected in the first spectrum and the wavelength shift is determined based on these multiple test structures, the wavelength shift can be measured with higher accuracy. For example, a wavelength shift can be determined for each test structure, and then the average of these wavelength shifts can be calculated, which is then used as the wavelength shift between the first and second spectra. Outliers occurring in a given case can be ignored. Alternatively, the test structures and their associated wavelength shifts can be weighted, for example, based on the signal-to-noise ratio of the test structures, which then affects the formation of the average.

[0025] In one embodiment, the first spectrum is divided into multiple sub-regions, and spectral structures within these sub-regions are selected as test structures. Because test structures are selected from different sub-regions of the first spectrum and the wavelength shift is determined based on comparisons of these test structures, higher accuracy of the determined wavelength shift is achieved.

[0026] In one embodiment, the comparison of a first and a second spectrum is based on the autocorrelation of the two spectra. The concept of autocorrelation originates from probability theory and signal processing, and it typically describes the correlation between a function or signal and itself at another point in time. In this invention, the autocorrelation function is used to compare the first and second spectra, where the first spectrum can be considered an earlier point in time of the second spectrum. Through autocorrelation, the degree to which the first and second spectra are similar or different can be examined. Thus, the wavelength shift between the first and second spectra can be determined.

[0027] In one embodiment, a sub-region is selected from both the first and second spectra, wherein the comparison between the first and second spectra is based on the autocorrelation of these two sub-regions. The sub-regions of the first and second spectra include the same regions of their respective spectra. Because only sub-regions of the spectra are compared, rather than the entire spectrum, wavelength shifts can be determined in a shorter time.

[0028] In one embodiment, the method further includes the following additional steps: - Collect the third spectrum, - The wavelength shift between the first and third spectra can be determined by comparing the first and third spectra, or the wavelength shift between the second and third spectra can be determined by comparing the second and third spectra. - Create a third wavelength association, wherein a wavelength is associated with a pixel in the third spectrum based on a wavelength offset determined between the second and third spectra or based on a wavelength offset determined between the first and third spectra.

[0029] Typically, not only the first and second spectra of the sample are acquired, but also additional spectra, such as the third, fourth, or fifth spectra. If another spectrum, such as the third spectrum, is acquired, the wavelength shift can also be determined for the third spectrum and any other spectra. On one hand, this can be based on a comparison of a previously acquired spectrum (e.g., the second spectrum) with the current spectrum (e.g., the third spectrum). Alternatively, the wavelength shift can be determined based on a comparison of an earlier spectrum (e.g., the first spectrum) with the current spectrum (e.g., the third spectrum). The third spectrum is particularly acquired after the first and second spectra.

[0030] In one embodiment, the method further includes the following additional steps: - Collect the third spectrum, - The wavelength shift between the second and third spectra is determined by extrapolating the wavelength shift between the first and second spectra. - Create a third wavelength association, where a wavelength is associated with a pixel in the third spectrum based on a wavelength offset determined between the second and third spectra.

[0031] In this embodiment, the wavelength shift between the first and second spectra is extrapolated to determine the wavelength shift between the second and third spectra. In this case, a first wavelength correlation and a second wavelength correlation can be used. This allows for the rapid creation of a third wavelength correlation. The third spectrum is acquired specifically after the first and second spectra.

[0032] In one embodiment, the method further includes the following additional steps: - Create the first wavelength association by associating the wavelength with the pixels of the detector. - The first spectrum of the acquired sample is used for first wavelength correlation, which is valid for this first spectrum. - Collect the second spectrum of the sample. - Acquire the third spectrum, which is acquired after the first spectrum and before the second spectrum. - The wavelength shift between the first and second spectra is determined by comparing the first and second spectra. - Create a second wavelength association, where wavelengths are associated with pixels in the second spectrum based on the determined wavelength offset between the first and second spectra. - The wavelength shift between the first and third spectra is determined based on the interpolation of the wavelength shift between the first and second spectra. - Create a third wavelength association, where a wavelength is associated with a pixel in the third spectrum based on a wavelength offset determined between the first and third spectra.

[0033] If the wavelength offset between two spectra (here, the first and second spectra) is known, this can be advantageously applied to interpolation calculations of the wavelength offset of a spectrum acquired between these two spectra (here, the third spectrum). This allows for the rapid creation of a third wavelength correlation.

[0034] In one embodiment, a reference spectrum is acquired, and a first wavelength association is created based on this reference spectrum. The reference spectrum can be acquired without a sample and using at least one reference light source having predetermined wavelengths. Wavelength-to-pixel association can be performed based on at least one predetermined wavelength of the at least one reference light source and the reference spectrum. Alternatively, other predetermined spectral structures can also be used for the first wavelength association. For example, a filter can be inserted into the beam path of the light generated between the sample unit and the detector, allowing only predetermined wavelengths to pass through. Based on the reference spectrum obtained through the filter, it is possible to detect which wavelengths of the filter have passed through and appeared on the detector, making wavelength association possible. The reference spectrum can also be the spectrum of the sample, in which additional predetermined spectral structures, such as those of a reference light source or filter, are added. The first wavelength association can also be created based on the spectral structure of the sample, especially when the components of the sample are at least partially known, or through pattern recognition, which generates patterns from the spectrum and compares them with a catalog of patterns to detect the components of the sample according to the patterns and create wavelength associations based on these components associated with predetermined wavelengths. Attached Figure Description

[0035] The invention will now be explained in more detail based on the accompanying drawings, the figures of which are shown below.

[0036] Figure 1 A schematic diagram of the spectrometer is shown.

[0037] Figure 2 The first spectrum is shown as an example.

[0038] Figure 3 A view showing the wavelength offset of the test structure is provided. Detailed Implementation

[0039] Figure 1A schematic diagram of a spectrometer 1 according to the present invention is shown. The spectrometer 1 includes a sample unit 3 and a detector 2. Optionally, the spectrometer 1 may have multiple optical components 5. The optical components 5 are arranged and implemented in such a way that they guide the beam path 8 of the generated light from the sample unit 3 to the detector 2. The detector 2 is implemented to detect the generated light in the form of a spectrum. The sample unit 3 may have a light source 4 that excites the sample to emit light or illuminates the sample to allow light to pass through it. The light source 4 may in particular be a plasma. The sample unit 3 may be implemented to focus the generated light and guide it to the main region 9 of the spectrometer. The sample unit 3 may have other optical components, such as an aperture stop 6, an input opening, a mirror, and a lens; some of these may not be shown to avoid clutter. The spectrometer 1 may have a slit 7. The slit 7 may be arranged between the sample unit 3 and the main region 9. The aperture stop 6 may be arranged adjacent to the slit 7. Optical components 5a, 5b, and 5c may be mirrors. As an example, optical component 5d is implemented as a mid-echelon grating. Other optical components may include filters, prisms, and / or lenses. Spectrometer 1 may be an ICP-OES device or an atomic absorption spectrometer.

[0040] Figure 2 The first spectrum is illustrated by an example. Several spectral structures exist within this first spectrum. The first spectrum in this example is a segment of a mid-level echelle spectrum acquired using an ICP-OES spectrometer. This segment was chosen to facilitate better identification of the spectral structures. In particular, these spectral structures are emission structures, which appear as bright regions against a dark plasma background. Due to thermal drift or other drifts, the positions of these emission structures on the detector may change over time. Therefore, for accurate evaluation of the spectrum, the correct wavelength correlation within the spectrum must always be ensured.

[0041] Therefore, in the method of this invention, firstly, a first wavelength correlation is created, for example, by using a reference spectrum. Then, a first spectrum and a second spectrum can be acquired. Based on a comparison of these two spectra, a wavelength shift is determined. In this case, the first wavelength correlation is valid for the first spectrum, which is acquired, for example, shortly after the reference spectrum and the first wavelength correlation. Due to thermal drift or other drifts, the first wavelength correlation is not necessarily valid for the second spectrum. A wavelength shift may have occurred between the first and second spectra, and this possibility must be investigated.

[0042] One of the multiple spectral structures in the first spectrum can be selected (i.e. Figure 2 The spectral structure circled in the box in the first spectrum is used as the test structure. Then, this test structure is located in the second spectrum. Based on the comparison between the test structure in the first spectrum and the test structure in the second spectrum, the wavelength shift between the first and second spectra can be determined.

[0043] Figure 3 The left side of the image shows a test structure in detail. Clearly, the closer to the center of the test structure, the higher the intensity; the further outward, the lower the intensity. Thus, the test structure exhibits an intensity distribution. The circle roughly located in the center of the image marks the center of this intensity distribution. Figure 3 The right side shows the change in the intensity center of the test structure over time. Therefore, the test structure in the first spectrum has the same intensity center, indicated by a circle. Due to thermal drift or other drift factors, the intensity center of the test structure initially shifts to the right and then gradually moves upwards in the view, as shown by the arrows. In this case, each arrow marks the intensity center of the test structure in a subsequently acquired spectrum. The dashed arrows mark the total wavelength shift over time. The wavelength shift, smaller than the pixel size, can be determined by evaluating the intensity center of the test structure. This can also be done in... Figure 3 As seen in the right-hand portion, which shows a 3×3 pixel area, the intensity center of the test structure shifts within one pixel in this case.

[0044] List of reference numerals

[0045] 1. Spectrometer

[0046] 2 Detectors

[0047] 3 Sample Units

[0048] 4. Light source

[0049] 5 Optical components

[0050] 6-aperture stop

[0051] 7. Slit

[0052] 8 Beam Path

[0053] 9 Main Area

Claims

1. A method for checking wavelength shift on detector (2) in a spectrometer (1), wherein, The spectrometer (1) includes a sample unit (3) and a detector (2), wherein the sample unit (3) is configured to generate the optical properties of the sample, particularly to excite the sample to emit light or to irradiate the sample with light passing through it, wherein the detector (2) has multiple pixels and is configured to detect the generated light as a spectrum, wherein the method includes the following steps: - Create a first wavelength association by associating the wavelength with the pixel of the detector (2). - Acquire the first spectrum of the sample, and the first wavelength correlation is valid for the first spectrum. - Acquire the second spectrum of the sample. - Determine the wavelength shift between the first and second spectra based on a comparison of the first and second spectra. - Create a second wavelength association, where a wavelength is associated with a pixel in the second spectrum based on the determined wavelength offset.

2. The method according to claim 1, in, The method includes the following steps: - Acquire a first spectrum of the sample, the first spectrum comprising multiple spectral structures, particularly emission structures, wherein at least one of the spectral structures in the first spectrum is selected as the test structure. - Acquire a second spectrum of the sample, and locate the test structure in the second spectrum. - The wavelength shift between the first and second spectra is determined based on a comparison of the test structures using the first and second spectra. - Create a second wavelength association, where a wavelength is associated with a pixel in the second spectrum based on the determined wavelength offset.

3. The method according to claim 2, in, The selected test structure is a spectral structure with a predetermined minimum area, minimum signal-to-noise ratio, and / or predetermined minimum intensity.

4. The method according to claim 2 or 3, in, The comparison of the test structure in the first spectrum and the second spectrum is based on the determination of the intensity center of the test structure.

5. The method according to claim 4, in, The wavelength shift corresponds to the difference between the intensity centers of the test structure in the first spectrum and the second spectrum.

6. The method according to claim 2 or 3, in, The comparison of the test structure in the first spectrum and the second spectrum is performed based on the edge of the test structure.

7. The method according to claim 2 or 3, in, The comparison of the test structures in the first spectrum and the second spectrum is performed by fitting the test structure to a second-order or higher-order function.

8. The method according to any one of claims 2 to 7, in, Based on the test structure, the test structure in the second spectrum is found at a first position in the first spectrum.

9. The method according to any one of claims 2 to 8, in, Locating the test structure in the second spectrum includes the following steps: - Determine the first position of the test structure in the first spectrum. - Locate the spectral structure in a predetermined region surrounding the first location within the second spectrum. - Compare the morphology of the test structure in the first spectrum with the morphology of the spectral structure found in the second spectrum. When the deviation between these two morphologies is within the tolerance range, the found spectral structure is determined to correspond to the test structure. The method is terminated when the deviation between these two forms exceeds the tolerance range.

10. The method according to any one of claims 2 to 9, in, Multiple spectral structures in the first spectrum are selected as test structures and the test structures are found in the second spectrum, wherein the wavelength shift between the first spectrum and the second spectrum is determined based on a comparison of the test structures in the first spectrum and the second spectrum.

11. The method according to claim 10, in, The first spectrum is divided into multiple sub-regions, and the spectral structure in each sub-region is selected as the test structure.

12. The method according to claim 1, in, The comparison between the first and second spectra is based on the autocorrelation between them.

13. The method according to claim 12, in, A sub-region is selected in the first spectrum and the second spectrum respectively, and the comparison between the first spectrum and the second spectrum is performed based on the autocorrelation of these two sub-regions of the first spectrum and the second spectrum.

14. The method according to any one of claims 1 to 13, in, The method further includes the following additional steps: - Collect the third spectrum, - The wavelength shift between the first spectrum and the third spectrum is determined based on a comparison of the first spectrum and the third spectrum, or the wavelength shift between the second spectrum and the third spectrum is determined based on a comparison of the second spectrum and the third spectrum. - Create a third wavelength association, wherein a wavelength is associated with a pixel in the third spectrum based on a wavelength offset determined between the second spectrum and the third spectrum or based on a wavelength offset determined between the first spectrum and the third spectrum.

15. The method according to any one of claims 1 to 14, in, A reference spectrum is acquired, and the first wavelength association is created based on the reference spectrum.

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