Wavelength calibration method, calibration sample, and wavelength calibration program

Abstract

To provide a new technique for performing a wavelength calibration.SOLUTION: A wavelength calibration method for a polychromator spectroscope equipped with a diffraction grating and a detector where light scattered by the diffraction grating forms an image, includes the steps of: applying light including a known bright line spectrum to the polychromator spectroscope and acquiring a first measurement result outputted from the spectroscope; applying reflected light or transmitted light resulting from irradiation with light of a calibration sample provided with a gap therein, and acquiring a second measurement result outputted from the spectroscope; determining a wavelength table so that the position of the known bright line spectrum in the first measurement result matches the wavelength of the known bright line spectrum; and repeating update of the wavelength table such that the error calculated on the basis of the second measurement result and the wavelength table is minimized.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a wavelength calibration method, a calibration sample, and a wavelength calibration program. [Background technology]

[0002] Polychromator spectrometers achieve high-speed measurements by using multi-channel detectors such as linear image sensors or area image sensors. Spectrometers require wavelength calibration, which determines the relationship between the detector's detection position (pixel number) and wavelength. In wavelength calibration, a wavelength table is created to determine the wavelength measured at each pixel of the detector.

[0003] In such wavelength calibration, a wavelength table is created by using a known emission line spectrum (e.g., Hg, Ar, Ne, Xe, etc.) as a reference and interpolating wavelength ranges other than the emission line spectrum (e.g., between adjacent emission line spectra).

[0004] Regarding such wavelength calibration, Japanese Patent Laid-Open Publication No. 2021-067611 (Patent Document 1) discloses a new technique that enables wavelength calibration even when the measurement wavelength range is narrow and a sufficient number of reference emission lines cannot be included in the measurement wavelength range. Japanese Patent Laid-Open Publication No. 2022-150580 (Patent Document 2) discloses a configuration that calibrates wavelengths with high precision without requiring a reference light source with a known wavelength, even when there is a possibility of a relatively large wavelength shift. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-067611 [Patent Document 2] Japanese Patent Publication No. 2022-150580 Summary of the Invention [Problem to be solved by the invention]

[0006] There may be cases where only one or no emission line spectrum exists within the measurement wavelength range of a high-resolution spectrometer. In such cases, it is not possible to create a wavelength table.

[0007] Japanese Patent Laid-Open Publication No. 2021-067611 (Patent Document 1) discloses a method using a standard sample. Japanese Patent Laid-Open Publication No. 2022-150580 (Patent Document 2) does not disclose any solution to this problem.

[0008] An object of the present invention is to provide a new method for performing wavelength calibration. [Means for solving the problem]

[0009] (Configuration 1) According to one aspect of the present invention, there is provided a wavelength calibration method for a polychromator spectrometer including a diffraction grating and a detector on which light dispersed by the diffraction grating is imaged. The wavelength calibration method includes the steps of: applying light containing a known emission line spectrum to the polychromator spectrometer and obtaining a first measurement result output from the detector; applying reflected or transmitted light generated by irradiating a calibration sample having an internal gap with the light to the polychromator spectrometer and obtaining a second measurement result output from the detector; and determining a wavelength table so that the position of the known emission line spectrum in the first measurement result matches the wavelength of the known emission line spectrum. The wavelength table indicates the correspondence between the detector output and wavelength. The wavelength calibration method also includes the step of repeatedly updating the wavelength table so as to minimize an error calculated based on the second measurement result and the wavelength table.

[0010] (Configuration 2) In configuration 1, the error may include an error between power spectra calculated from each waveform obtained by dividing the waveform calculated from the second measurement result using a wavelength table with respect to wavelength.

[0011] (Configuration 3) In configuration 1 or 2, the error may include an error between a waveform calculated from the second measurement result using the wavelength table and a simulation waveform calculated based on a model of the calibration sample.

[0012] (Configuration 4) In configuration 3, the wavelength calibration method may further include a step of determining the thickness of the gap in the calibration sample when the error is minimized.

[0013] (Configuration 5) In configuration 4, the wavelength calibration method further includes the steps of changing the positional relationship of the diffraction gratings of the polychromator spectrometer, applying reflected or transmitted light generated by irradiating light onto the calibration sample to the polychromator spectrometer with the positional relationship of the diffraction gratings changed, and obtaining a third measurement result output from the detector, and repeatedly updating the wavelength table so as to minimize the error between a waveform calculated from the third measurement result using the wavelength table and a simulation waveform calculated based on a model of the calibration sample with the determined gap thickness fixed.

[0014] (Configuration 6) In any of configurations 1 to 5, the step of repeatedly updating the wavelength table may include a step of maintaining the wavelengths of the emission line spectrum in the optical spectrum calculated from the first measurement result using the updated wavelength table to match the wavelengths of the known emission line spectrum.

[0015] (Configuration 7) A calibration sample for use in the wavelength calibration method according to any one of configurations 1 to 6 is provided.

[0016] (Configuration 8) According to another aspect of the present invention, there is provided a wavelength calibration program for calibrating the wavelength of a polychromator spectrometer including a diffraction grating and a detector on which light dispersed by the diffraction grating is imaged. The wavelength calibration program causes a computer to execute the following steps: acquiring a first measurement result output from the detector when light containing a known emission line spectrum is applied to the polychromator spectrometer; acquiring a second measurement result output from the detector when the polychromator spectrometer is applied with reflected or transmitted light generated by irradiating a calibration sample having a gap therein with the light; and determining a wavelength table so that the position of the known emission line spectrum in the first measurement result matches the wavelength of the known emission line spectrum. The wavelength table indicates the correspondence between the detector output and wavelength. The wavelength calibration program causes the computer to execute the step of repeatedly updating the wavelength table so as to minimize an error calculated based on the second measurement result and the wavelength table. [Effects of the Invention]

[0017] According to an embodiment of the present invention, a new method for performing wavelength calibration can be provided. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a schematic diagram illustrating a configuration example of a polychromator spectroscope. [Figure 2] FIG. 10 is a diagram illustrating an example of wavelength calibration for a broadband spectrometer. [Figure 3] FIG. 10 is a diagram illustrating an example of wavelength calibration for a high-resolution spectrometer. [Figure 4] FIG. 10 is a diagram showing an example of a measurement result of an emission line spectrum obtained by a high-resolution spectrometer. [Figure 5] FIG. 1 is a schematic diagram showing an example of a measurement system for performing a first wavelength calibration method according to the present embodiment. [Figure 6] FIG. 2 is a schematic diagram showing an example of the configuration of a calibration sample used in the first wavelength calibration method according to the present embodiment. [Figure 7]6 is a graph showing an example of the results of measuring a calibration sample with an air gap thickness of approximately 100 μm using the measurement system shown in FIG. 5. [Figure 8] 5 is a flowchart showing an example of a processing procedure of a first wavelength calibration method according to the present embodiment. [Figure 9] 9 shows an example of an optical spectrum calculated from the measurement results of the light source in step S4 of FIG. [Figure 10] 8 shows an example of an optical spectrum calculated using the wavelength table f1(λ) determined in step S8 of FIG. [Figure 11] 6 is a graph showing a processing example of the first wavelength calibration method according to the present embodiment. [Figure 12] 6 is a graph showing a processing example of the first wavelength calibration method according to the present embodiment. [Figure 13] 6 is a graph showing a processing example of the first wavelength calibration method according to the present embodiment. [Figure 14] 9 is an example of a spectrum calculated using a wavelength table f(λ) determined by the first wavelength calibration method shown in FIG. 8. [Figure 15] 10 is a flowchart showing an example of a processing procedure of a second wavelength calibration method according to the present embodiment. [Figure 16] 10 is a graph showing an example of measurement results used in the second wavelength calibration method according to the present embodiment. [Figure 17] An example of the optical spectrum calculated from the measurement results of the light source in step S52 of FIG. 15 using the wavelength table f0(λ) and the wavelength table f1(λ) is shown. [Figure 18] 16 is a graph showing an example of an optical spectrum calculated using a wavelength table f1(λ) from the measurement results of the calibration sample in step S54 of FIG. 15. [Figure 19] 16 is a graph showing an example of the results of fitting performed in step S62 of FIG. 15. [Figure 20]An example of a spectroscopic spectrum calculated using the wavelength table f(λ) determined by the second wavelength calibration method shown in FIG. 15. [Figure 21] FIG. 3 is a flowchart showing an example of a processing procedure of a third wavelength calibration method according to the present embodiment. [Figure 22] FIG. 6 is a graph showing an example of a processing example of the third wavelength calibration method according to the present embodiment. [Figure 23] FIG. 9 is a graph showing an example of a processing example of the third wavelength calibration method according to the present embodiment. [Figure 24] An example of a spectroscopic spectrum calculated using the wavelength table f(λ) determined by the third wavelength calibration method shown in FIG. 21. [Figure 25] FIG. 15 is a schematic diagram showing a configuration example of an information processing apparatus for executing the wavelength calibration method according to the present embodiment. MODE FOR CARRYING OUT THE INVENTION

[0019] Embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals and their description will not be repeated.

[0020] <A. Configuration Example of a Polychromator Spectrometer> First, a configuration example of a polychromator spectrometer 1 to which the wavelength calibration method according to the present embodiment can be applied will be described. The wavelength calibration method according to the present embodiment is applied to a polychromator spectrometer including a diffraction grating and a detector on which light dispersed by the diffraction grating is imaged.

[0021] FIG. 1 is a schematic diagram showing a configuration example of the polychromator spectrometer 1. Referring to FIG. 1, the polychromator spectrometer 1 (hereinafter also simply abbreviated as "spectrometer 1") includes a slit 10, a collimating mirror 12, a grating 14, a focusing mirror 16, a detector 18, and a processing unit 20.

[0022] 1 shows an example of a Czerny-Turner type optical system, but any type of optical system may be used for the spectrometer 1. For example, a Fastie-Ebert type optical system may be used.

[0023] Light to be measured (sample light 2) passes through a slit 10 and enters a collimating mirror 12. The slit 10 adjusts the width of the image of the sample light 2 on a detector 18. The sample light 2 may be obtained from any source.

[0024] The collimating mirror 12 reflects the sample light 2 that has passed through the slit 10 and is incident thereon, converting it into parallel light, and also guides the parallel light to the diffraction grating 14 .

[0025] The diffraction grating 14 is an optical element for dispersing the sample light 2 from the collimating mirror 12. The diffraction grating 14 separates the incident sample light 2 from the collimating mirror 12 according to wavelength and guides it to the detector 18. The diffraction grating 14 is a reflective diffraction grating configured to reflect diffracted waves at predetermined wavelength intervals in corresponding directions. When the sample light 2 from the collimating mirror 12 is incident on the diffraction grating 14, each wavelength component contained in the sample light 2 is reflected in the corresponding direction. The diffraction grating 14 may be, for example, a blazed holographic plane grating.

[0026] The focus mirror 16 reflects the light reflected by the diffraction grating 14 in directions according to the wavelengths, and forms an image on the detector 18 .

[0027] The detector 18 is, for example, a multi-channel detector such as a linear image sensor or an area image sensor. The detector 18 has a plurality of aligned pixels (channels), and outputs an electrical signal indicating the intensity of light incident on each pixel. In the following explanation, a configuration example using the detector 18 made of a linear image sensor will be mainly described.

[0028] Based on the wavelength table 22, the processing unit 20 calculates the spectral spectrum 4 from the electrical signal (output value for each pixel) from the detector 18.

[0029] The wavelength table 22 shows the correspondence between the output of the detector 18 and the wavelength. More specifically, the wavelength table 22 is calibration information indicating the correspondence between the pixel number of the detector 18 and the wavelength included in the sample light 2. The entity of the wavelength table 22 may be a table associating the pixel number with the wavelength, or may be a function indicating the correspondence between the pixel number and the wavelength.

[0030] The processing unit 20 may be built into the spectroscope 1 or may be arranged outside the spectroscope 1.

[0031] In the spectroscope 1 shown in FIG. 1, a shutter for blocking the incidence of the sample light 2 may be arranged. In the spectroscope 1 shown in FIG. 1, a cut filter for limiting the unwanted wavelength components included in the sample light 2 may be arranged.

[0032] Not limited to the optical system shown in FIG. 1, the collimating mirror 12 and the focusing mirror 16 may be arranged at different positions. Another mirror having the function of the collimating mirror 12 or the function of the focusing mirror 16 may be arranged. A single mirror having the functions of both the collimating mirror 12 and the focusing mirror 16 may be arranged.

[0033] <000,0176><B. Background Art of Wavelength Calibration> Next, the background art of wavelength calibration will be described.

[0034] Referring to FIG. 1, the imaging position λ of the slit image spectrally decomposed by the diffraction grating 14 in the spectroscope 1 is theoretically calculated according to the following grating equation using the incident angle α, the diffraction angle β, the number of rulings N, and the order m.

[0035] λ = (sin α + sin β) / (N × m) The imaging position λ of the slit image also depends on the curvature of the focus mirror 16 and the positions of the collimator mirror 12 and the focus mirror 16. The size of the slit image also depends on the curvature of the collimator mirror 12 and the curvature of the focus mirror 16.

[0036] However, due to the influence of component errors (number of rulings, curvature, placement position, processing errors, etc.) and adjustment errors of the optical components that make up the optical system, the wavelengths imaged on each pixel of detector 18 do not strictly match the calculated results (theoretical values).

[0037] Therefore, it is necessary to measure a light source (such as a mercury lamp, argon lamp, neon lamp, or xenon lamp) that emits light containing a known emission line spectrum, and assign which wavelengths the pixels of the detector 18 correspond to based on the position of each emission line spectrum (hereinafter also referred to as "emission line position"). This assignment operation is called wavelength calibration.

[0038] Fig. 2 is a diagram showing an example of wavelength calibration for a broadband spectrometer. Fig. 2 shows an example of the results of measuring a mixed lamp consisting of a mercury lamp and an argon lamp using a spectrometer with a measurement wavelength range of 200 to 1100 nm.

[0039] FIG. 2(A) is a graph showing the relationship between pixel number and intensity of detector 18. FIG. 2(B) is a graph showing the relationship between wavelength and intensity. The graph shown in FIG. 2(B) was created by converting pixel numbers of detector 18 to wavelengths based on the emission line spectrum appearing in the graph shown in FIG. 2(A). More specifically, a third-order polynomial was created from the center of gravity positions indicated by the waveforms near each emission line position, and the wavelength corresponding to each pixel number was determined based on the created third-order polynomial.

[0040] The position (wavelength) of each emission line was determined by referring to the Scientific Chronology and the NIST Atomic Spectra Database Lines.

[0041] As shown in FIG. 2, when a plurality of bright line spectra exist within the measurement wavelength range, wavelength allocation to each pixel of the detector 18 can be performed relatively easily.

[0042] Fig. 3 is a diagram showing an example of wavelength calibration for a high-resolution spectrometer, showing an example of the results of measuring a mercury lamp with a spectrometer having a measurement wavelength range of 540 to 585 nm.

[0043] Figure 3(A) is a graph showing the relationship between pixel number and intensity of the detector 18. Figure 3(B) is a graph showing the relationship between wavelength and intensity. The position (wavelength) of each emission line was determined by referring to the Scientific Chronology and the NIST Atomic Spectra Database Lines.

[0044] In the graph shown in Figure 3(A), there are three bright line spectra within the measurement wavelength range, but the two on the right are close to each other, so polynomial approximation would result in a large wavelength calibration error. Therefore, the influence of optical components that may occur in each pixel of the detector 18 was defined as a trigonometric function variable, and the wavelength to be assigned to each pixel number was determined by searching for variables (using the least squares method) that minimize the sum of squares of the baseline position residual.

[0045] Fig. 4 is a diagram showing an example of the measurement results of a line spectrum using a high-resolution spectrometer. Fig. 4 shows an example of the results of measuring a mercury lamp using a spectrometer with a measurement wavelength range of 505 to 550 nm. In the graph shown in Fig. 4, there is only one line spectrum within the measurement wavelength range, so conventional wavelength calibration methods cannot be applied.

[0046] The wavelength calibration method according to this embodiment can create a wavelength table even when there is only one bright line spectrum within the measurement wavelength range as shown in Fig. 4, or when there is no bright line spectrum within the measurement wavelength range. The wavelength calibration method according to this embodiment will be described in detail below.

[0047] <C.1 First Wavelength Calibration Method Based on Emission Line Spectrum and Interference Waveform of the Present Invention> When there is one emission line spectrum within the measurement wavelength range, wavelength calibration is performed using the interference waveform measured using a calibration sample described later.

[0048] FIG. 5 is a schematic diagram showing an example of a measurement system 100 for performing the first wavelength calibration method according to the present embodiment. Referring to FIG. 5, the measurement system 100 includes a spectroscope 1, a light source 30, and a Y-shaped fiber 40.

[0049] The light generated by the light source 30 is irradiated onto the calibration sample 50, and the reflected light from the calibration sample 50 is measured by the spectroscope 1. FIG. 5 shows an example of a reflection optical system for measuring the reflectance of the calibration sample 50, but a transmission optical system for measuring the transmittance of the calibration sample 50 may also be employed.

[0050] The light source 30 may be, for example, a tungsten lamp. The light generated by the light source 30 enters from the end 41 of the Y-shaped fiber 40 and is irradiated from the light transmitting / receiving probe 42 toward the calibration sample 50. The reflected light from the calibration sample 50 enters the light transmitting / receiving probe 42 of the Y-shaped fiber 40 and enters the spectroscope 1 from the end 43.

[0051] An information processing device 200 for performing wavelength calibration (that is, for creating a wavelength table) may be connected to the spectroscope 1. Details of the information processing device 200 will be described later.

[0052] FIG. 6 is a schematic diagram showing a configuration example of the calibration sample 50 used in the first wavelength calibration method according to the present embodiment. Referring to FIG. 6, a gap for generating an interference waveform is provided inside the calibration sample 50. The gap may be an air gap filled with air or a vacuum gap with the gap evacuated. When the gap of the calibration sample 50 is a vacuum gap, the calibration sample 50 is arranged inside a vacuum container. In the following description, an example of an air gap will be mainly described.

[0053] The calibration sample 50 includes anti-reflection coatings 51 and 55, quartz plates 52 and 54, and a shim 53.

[0054] The antireflection films 51 and 55 are made of, for example, magnesium fluoride (MgF2) and are disposed on both sides of the calibration sample 50. For example, the thickness of the antireflection film 51 is 97.277 nm, and the thickness of the antireflection film 55 is 95.841 nm (both are actual values ​​measured using a microspectrophotometer).

[0055] Antireflection films 51 and 55 are respectively formed on the quartz plates 52 and 54 by, for example, vapor deposition etc. The thickness of each of the quartz plates 52 and 54 is, for example, about 2.5 mm.

[0056] An air gap 58 is provided by providing a shim 53 between the quartz plate 52 and the quartz plate 54. The thickness of the shim 53 may be, for example, about 100 μm or about 20 μm. That is, the thickness of the air gap 58 may be selected from about 100 μm and about 20 μm. The thickness of the shim 53 (i.e., the air gap 58) may be designed as desired depending on the emission line position, etc.

[0057] The calibration sample 50 may be provided with an air hole 56. By connecting the air gap 58 to the outside air through the air hole 56, the internal pressure of the air gap 58 can be made equal to atmospheric pressure. This makes it possible to prevent fluctuations in the thickness of the air gap 58 due to fluctuations in the internal pressure of the air gap 58.

[0058] FIG. 7 is a graph showing an example of the results of measuring a calibration sample 50 in which the air gap 58 has a thickness of about 100 μm using the measurement system 100 shown in FIG.

[0059] Referring to Fig. 7, interference occurring in the air gap 58 of the calibration sample 50 is observed. The graph shown in Fig. 7 shows reflectances associated with pixel numbers of the detector 18. The reference waveform for calculating the reflectance is measured by a known method. In this embodiment, wavelength calibration is performed using the interference waveform shown in Fig. 7.

[0060] FIG. 8 is a flowchart showing an example of a processing procedure of the first wavelength calibration method according to the present embodiment. Referring to FIG. 8, a wavelength table f0(λ) is calculated based on the design values ​​of the spectrometer 1 (step S2). The wavelength table indicates the relationship between the imaging position λ of the slit image in the spectrometer 1 and the wavelength f of the slit image. The imaging position λ may be defined as a variable indicating the pixel number of the detector 18. For example, if the detector 18 has 1024 channels, the imaging position λ may be set to take a value from 0 to 1023 (or from 1 to 1024). The wavelength f incident on each pixel (channel) is obtained by inputting a natural number indicating the pixel number (channel number) of each pixel as the imaging position λ into the wavelength table f0(λ).

[0061] The wavelength table f0(λ) can be calculated using the above-mentioned grating equation, including trigonometric functions. However, to facilitate the update process described later, the calculated wavelength table f0(λ) may be approximated by a polynomial (e.g., a third-order polynomial). For example, f(λ)=aλ 3 +bλ 2 It can also be defined as +cλ+d, where a, b, and c are coefficients for the imaging position λ, and d is the intercept. The same applies to the wavelength calibration methods below.

[0062] Light containing a known emission line spectrum is measured using detector 18 (step S4). That is, light containing a known emission line spectrum is applied to spectrometer 1, and a measurement result (first measurement result) is output from detector 18. A mercury lamp may be used as the light source. In this case, the known emission line position (wavelength) is 546.07498 nm.

[0063] 5, calibration sample 50 is measured (step S6). That is, calibration sample 50, which has air gap 58 provided therein, is irradiated with light, and the resulting reflected light (or transmitted light) is applied to spectrometer 1, and a measurement result (second measurement result) is obtained as an output from detector 18. The measurement result in step S6 indicates a change in reflectance (or transmittance) for the pixel number (imaging position λ) of detector 18.

[0064] The calculation of the wavelength table f0(λ) in step S2, the measurement in step S4, and the measurement in step S6 may be performed in any order.

[0065] The wavelength table f0(λ) is shifted in the wavelength direction so that it coincides with the emission line position indicated by the measurement result in step S4, and thus the wavelength table f1(λ) (≡f0(λ+Δλ)) is determined (step S8). That is, the wavelength table f1(λ) is determined so that the position of the known emission line spectrum in the measurement result (first measurement result) in step S4 coincides with the wavelength of the known emission line spectrum. The updated wavelength table f1(λ) is set as the current wavelength table f(λ).

[0066] Subsequently, the wavelength table is repeatedly updated (steps S10 to S18) so as to minimize the error calculated based on the measurement result (second measurement result) in step S6 and the wavelength table.

[0067] Using the current wavelength table f(λ), a spectrum representing the interference waveform is calculated from the measurement results in step S6 (step S10). The calculated spectrum is divided into three wavelength ranges (step S12). Hereinafter, the three divided waveforms will be referred to as the short wavelength waveform, the medium wavelength waveform, and the long wavelength waveform, respectively, from the short wavelength side.

[0068] Next, power spectra are calculated from the short wavelength waveform, the medium wavelength waveform, and the long wavelength waveform (step S14). The errors between the power spectra calculated from the short wavelength waveform, the medium wavelength waveform, and the long wavelength waveform are recorded in association with the current wavelength table (step S16).

[0069] It is determined whether a termination condition is met (step S18). The termination condition may be, for example, that the processes of steps S10 to S16 have been performed a predetermined number of times. Alternatively, the termination condition may be that the error between the power spectra is equal to or less than a predetermined threshold value.

[0070] If the termination condition is not met (NO in step S18), the coefficients and intercepts of the current wavelength table f(λ) are updated based on the errors between the power spectra calculated from the short-wavelength waveform, the medium-wavelength waveform, and the long-wavelength waveform (step S20). Then, the processing from step S10 onwards is repeated.

[0071] In updating the coefficients and intercepts of the wavelength table f(λ), the emission line positions indicated by the measurement results in step S4 are used as constraints. That is, in the process of repeatedly updating the wavelength table f(λ), it is maintained that the wavelengths of the emission line spectra match the wavelengths of the known emission line spectra in the optical spectrum calculated from the measurement results (first measurement results) in step S4 using the updated wavelength table f(λ).

[0072] If the termination condition is met (YES in step S18), the wavelength table with the smallest error between the recorded power spectra is output as the result of wavelength calibration (step S22).

[0073] In this way, in the first wavelength calibration method, the waveform calculated from the measurement result (second measurement result) in step S6 is divided by wavelength using the wavelength table f(λ), and the error between the power spectra calculated from each waveform is used. A wavelength table f(λ) that minimizes the error between the power spectra is searched for.

[0074] The number of divisions into the optical spectrum does not have to be three, but may be two, four or more.

[0075] A processing example of the first wavelength calibration method shown in FIG. 8 will be described below.

[0076] Fig. 9 shows an example of a spectrum calculated from the measurement results of the light source in step S4 of Fig. 8. Fig. 9 shows an example of the measurement results of a mercury lamp. Fig. 9 shows an example of a spectrum calculated from the measurement results using a wavelength table f0(λ). Fig. 9(A) shows a graph of the spectrum over the measurement wavelength range of 505 to 550 nm. Fig. 9(B) shows a graph of the spectrum near the emission line position.

[0077] The emission line position should be 546.07498 nm, but as shown in Figure 9(B), the center of gravity of the waveform near the emission line position of the spectrum calculated using the wavelength table f0(λ) is 545.9652 nm. In other words, it can be seen that an error of 0.109736 nm has occurred in the emission line position. Since the pixel resolution for the measurement wavelength range of 505 to 550 nm is approximately 0.045 nm, an error of more than two pixels has occurred.

[0078] In step S8 of Fig. 8, the wavelength table f0(λ) is shifted in the wavelength direction to correct the error in the emission line position, and the wavelength table f1(λ) is determined. In the example shown in Fig. 9, the wavelength table f0(λ) is shifted to the long wavelength side.

[0079] Fig. 10 shows an example of a spectrum calculated using the wavelength table f1(λ) determined in step S8 of Fig. 8. Fig. 10(A) shows a graph of the spectrum over the measurement wavelength range of 505 to 550 nm. Fig. 10(B) shows a graph of the spectrum near the emission line position.

[0080] As shown in FIG. 10, it can be seen that by using the wavelength table f1(λ), ​​the calculated emission line positions match the known emission line positions.

[0081] 11 to 13 are graphs showing a processing example of the first wavelength calibration method according to the present embodiment, in which a calibration sample 50 having an air gap 58 with a thickness of about 100 μm is used.

[0082] 11(A) is a graph showing a spectrum 80 calculated using a wavelength table f0(λ) calculated based on the design values ​​of the spectrometer 1. The spectrum 80 is divided into three parts in the wavelength direction to determine a short wavelength waveform 82, a medium wavelength waveform 84, and a long wavelength waveform 86. In the example shown in FIG. 11(A), each of the short wavelength waveform 82, the medium wavelength waveform 84, and the long wavelength waveform 86 has a wavelength width of 15 nm.

[0083] 11(B) is a graph showing the power spectrum calculated by performing frequency analysis (e.g., FFT) on each of the short wavelength waveform 82, the medium wavelength waveform 84, and the long wavelength waveform 86. The power spectrum is normalized so that the maximum value is 1 (the same applies hereinafter).

[0084] The peak position of the calculated power spectrum indicates the thickness of the air gap 58 that generates the interference waveform in the calibration sample 50. Note that, in wavelength calibration, it is not necessary to precisely determine the thickness of the air gap 58 in the calibration sample 50.

[0085] Referring to each power spectrum shown in Figure 11(B), the peak position of the power spectrum calculated from the short wavelength waveform 82 is 102.175 μm, the peak position of the power spectrum calculated from the medium wavelength waveform 84 is 102.103 μm, and the peak position of the power spectrum calculated from the long wavelength waveform 86 is 102.092 μm.

[0086] That is, the peak position of the power spectrum calculated from the short wavelength waveform 82 indicates a relatively large film thickness, and the peak position of the power spectrum calculated from the long wavelength waveform 86 indicates a relatively small film thickness. From this, it can be seen that in wavelength table f1(λ), ​​the chromatic dispersion on the short wavelength side is smaller than the chromatic dispersion on the medium wavelength side, and the chromatic dispersion on the long wavelength side is larger than the chromatic dispersion on the medium wavelength side.

[0087] Therefore, the coefficients and intercepts of wavelength table f1(λ) are updated so that the chromatic dispersion on the short wavelength side increases and the chromatic dispersion on the long wavelength side decreases. In the example shown in Fig. 11(B), the coefficients for the imaging position λ in wavelength table f1(λ) are updated so that the increase in the imaging position λ decreases, and the intercepts of wavelength table f1(λ) are updated so that the emission line position of the light source used in the measurement of step S4 does not deviate. Using the updated wavelength table f2(λ), the processing from step S10 onwards is repeated.

[0088] Fig. 12(A) is a graph showing an optical spectrum 80 calculated using the updated wavelength table f1(λ). Referring to the power spectra shown in Fig. 12(B), the peak position of the power spectrum calculated from the short wavelength waveform 82 is 102.238 μm, the peak position of the power spectrum calculated from the medium wavelength waveform 84 is 102.247 μm, and the peak position of the power spectrum calculated from the long wavelength waveform 86 is 102.270 μm.

[0089] That is, the peak position of the power spectrum calculated from the short wavelength waveform 82 indicates a relatively small film thickness, and the peak position of the power spectrum calculated from the long wavelength waveform 86 indicates a relatively large film thickness. From this, it can be seen that in wavelength table f1(λ), ​​the chromatic dispersion on the short wavelength side is larger than the chromatic dispersion on the medium wavelength side, and the chromatic dispersion on the long wavelength side is smaller than the chromatic dispersion on the medium wavelength side.

[0090] Therefore, the coefficients and intercepts of wavelength table f1(λ) are updated so that the chromatic dispersion on the short wavelength side becomes smaller and the chromatic dispersion on the long wavelength side becomes larger. In the example shown in Fig. 12(B), the coefficients for the imaging position λ in wavelength table f1(λ) are updated so that the increment for the imaging position λ increases, and the intercepts of wavelength table f1(λ) are updated so that the emission line position of the light source used in the measurement of step S4 does not deviate. Using the updated wavelength table f2(λ), the processing from step S10 onwards is repeated.

[0091] FIG. 13(A) shows the final wavelength table f n 13(B) is a graph showing an optical spectrum 80 calculated using wavelength table f(λ). Referring to each power spectrum shown in FIG. 13(B), the peak position of the power spectrum calculated from the short wavelength waveform 82 is 102.223 μm, the peak position of the power spectrum calculated from the medium wavelength waveform 84 is 102.218 μm, and the peak position of the power spectrum calculated from the long wavelength waveform 86 is 102.224 μm. As can be seen, by repeatedly updating the wavelength table f(λ), the error between the power spectra is reduced to 0.006 μm.

[0092] FIG. 14 shows an example of a spectrum calculated using the wavelength table f(λ) determined by the first wavelength calibration method shown in FIG.

[0093] In the first wavelength calibration method, the interference waveform obtained by measuring the calibration sample 50 is divided into a plurality of parts, and the coefficients and intercepts of the function indicating the theoretical values of the wavelength table are repeatedly updated so that the results obtained by performing frequency analysis on each of the divided interference waveforms match each other. Note that in the update of the coefficients and intercepts of the function, known bright line positions are used as constraint conditions.

[0094] As described above, it is not necessary for the thickness of the air gap 58 of the calibration sample 50 to be known. The thickness of the air gap 58 may be measured from the analysis results when the wavelength table is determined.

[0095] <T Strictly speaking, the refractive index of the air gap 58 depends on the environment, but the influence on the determined wavelength table can be ignored. For example, referring to the Science Yearbook, the refractive index of dry air with 0.03% carbon dioxide, at 15 °C, and 0.101325 MPa at a wavelength of 505 nm is 1.000278241. During the experiments shown in FIGS. 11 to 13, the atmospheric pressure was 1009 hPa, the room temperature was 25.4 °C, and the humidity was 40%.

[0096] Assuming that the environmental dependence of the refractive index is 0.00000027 / hPa, -0.000001 / °C, and -0.00000007 / % humidity, the refractive index can be calculated as 1.000267006. Also, the refractive index at a wavelength of 550 nm can be calculated as 1.000265999. The difference between the two is 0.00000101, and the error can be ignored even if the refractive index is handled uniformly. That is, even if the refractive index is regarded as 1, only the result of multiplying the original thickness of the air gap 58 by the environmental dependence coefficient is output, and no error occurs in the wavelength table f(λ).

[0097] <D. Second Wavelength Calibration Method Based on a Single Bright Line Spectrum and Interference Waveform> In the first wavelength calibration method, a method of determining the wavelength table using the result of frequency analysis of the interference waveform was exemplified, but the wavelength table may be determined by simulating the interference waveform.

[0098] 15 is a flowchart showing an example of a processing procedure of the second wavelength calibration method according to the present embodiment. Referring to Fig. 15, a wavelength table f0(λ) is calculated based on the design values ​​of spectrometer 1 (step S50).

[0099] Light containing a known emission line spectrum is measured using detector 18 (step S52). That is, light containing a known emission line spectrum is applied to spectrometer 1, and a measurement result (first measurement result) is obtained as an output from detector 18. A mercury lamp may be used as the light source. In this case, the known emission line position (wavelength) is 546.07498 nm.

[0100] 5, calibration sample 50 is measured (step S54). That is, calibration sample 50, which has air gap 58 provided therein, is irradiated with light, and the resulting reflected light (or transmitted light) is applied to spectrometer 1, and a measurement result (second measurement result) is obtained as an output from detector 18. The measurement result in step S54 indicates a change in reflectance (or transmittance) for the pixel number (imaging position λ) of detector 18.

[0101] The calculation of the wavelength table f0(λ) in step S50, the measurement in step S52, and the measurement in step S54 may be performed in any order.

[0102] The wavelength table f1(λ) is determined by shifting the wavelength table f0(λ) in the wavelength direction so that it coincides with the emission line position indicated by the measurement result in step S52 (step S56). That is, the wavelength table f1(λ) is determined so that the position of the known emission line spectrum in the measurement result (first measurement result) in step S52 coincides with the wavelength of the known emission line spectrum. The calculated wavelength table f1(λ) is set as the current wavelength table f(λ).

[0103] Subsequently, the wavelength table is repeatedly updated (steps S58 to S64) so ​​as to minimize the error calculated based on the measurement result (second measurement result) in step S54 and the wavelength table.

[0104] In the process of repeatedly updating the wavelength table f(λ), the wavelengths of the emission line spectrum in the optical spectrum calculated from the measurement result (first measurement result) in step S52 using the updated wavelength table f(λ) are maintained to match the wavelengths of the known emission line spectrum.

[0105] Using the current wavelength table f(λ), a spectrum showing an interference waveform is calculated from the measurement results in step S54 (step S58).

[0106] A model of the calibration sample 50 is created using the thickness of the air gap 58 as a variable parameter (step S60). Fitting is performed so as to maximize the degree of agreement between a simulation waveform calculated based on the model of the calibration sample 50 and the optical spectrum representing the interference waveform calculated in step S58 (step S62). The degree of agreement obtained by fitting is recorded in association with the current wavelength table (step S64).

[0107] It is determined whether or not a termination condition is met (step S66). The termination condition may be, for example, that fitting has been performed a predetermined number of times.

[0108] If the termination condition is not met (NO in step S66), the coefficients and intercepts of the current wavelength table f(λ) are updated (step S68). In updating the coefficients and intercepts of the wavelength table f(λ), the emission line position indicated by the measurement result in step S52 is used as a constraint. Then, the processing from step S58 onwards is repeated.

[0109] If the termination condition is met (YES in step S66), the wavelength table with the highest degree of match among the performed fittings is output as the wavelength calibration result (step S70). Also, the thickness of the air gap 58 of the calibration sample 50 in the model with the highest degree of match is output (step S72).

[0110] In this way, in the second wavelength calibration method, the error between the waveform calculated from the measurement result (second measurement result) in step S54 using the wavelength table f(λ) and the simulation waveform calculated based on the model of the calibration sample 50 is used. A wavelength table f(λ) that minimizes the error between the waveforms is searched for. The thickness of the air gap 58 that is output is the value (most likely value) when the error between the waveforms is minimized.

[0111] A processing example of the second wavelength calibration method shown in FIG. 15 will be described below.

[0112] Fig. 16 is a graph showing an example of measurement results used in the second wavelength calibration method according to the present embodiment, where the measurement results are obtained using a spectroscope with a measurement wavelength range of 505 to 550 nm.

[0113] Fig. 16(A) is a graph showing an example of the measurement results of light containing a known emission line spectrum, measured in step S52 of Fig. 15. Fig. 16(A) shows an example of the measurement results of a mercury lamp. The known emission line position (wavelength) is 546.07498 nm.

[0114] Fig. 16(B) is a graph showing an example of the measurement results of the calibration sample 50 measured in step S54 of Fig. 15. Fig. 16(B) shows the measurement results of the calibration sample 50 in which the thickness of the air gap 58 is about 20 µm.

[0115] Fig. 17 shows examples of spectra calculated using wavelength tables f0(λ) and f1(λ) from the light source measurement results in step S52 of Fig. 15. Fig. 17(A) shows the vicinity of the emission line positions of the spectrum calculated using wavelength table f0(λ). Fig. 17(B) shows the vicinity of the emission line positions of the spectrum calculated using wavelength table f1(λ).

[0116] The wavelength table f1(λ) is determined by shifting the wavelength table f0(λ) in the wavelength direction so as to correct the error in the emission line position. In the example shown in Fig. 17, the wavelength table f0(λ) is shifted to the long wavelength side.

[0117] Fig. 18 is a graph showing an example of an optical spectrum calculated using wavelength table f1(λ) from the measurement results of calibration sample 50 in step S54 of Fig. 15. Fig. 18(A) shows an example of the results of measuring calibration sample 50 having an air gap 58 with a thickness of approximately 20 μm using measurement system 100 shown in Fig. 5. Fig. 18(B) shows an example of an optical spectrum calculated using wavelength table f1(λ) from the measurement results shown in Fig. 18(A).

[0118] The thickness of the air gap 58 is changed in the model of the calibration sample 50 so that the optical spectrum (measured waveform) calculated using the wavelength table matches the simulated waveform calculated based on the calibration sample 50. That is, fitting is performed on the thickness of the air gap 58 of the calibration sample 50. Since the waveforms are compared, curve fitting may be used.

[0119] A model of the calibration sample 50 was constructed using the following parameters:

[0120] ·Anti-reflection coating 51 (MgF2:97.277nm) Quartz plate 52 (non-interference film: approx. 2.5 mm) Air gap 58 (thickness: approx. 20 μm) Quartz plate 54 (non-interference film: approx. 2.5 mm) ·Anti-reflection coating 55 (MgF2:95.841nm) The thickness of the quartz plates 52 and 54 is unknown, and they are considered to be non-interfering films when calculating the simulation waveform.

[0121] In fitting, the degree of match was used. The degree of match is an index showing the degree to which the optical spectrum (measured waveform) and the simulation waveform match. If the two waveforms match perfectly, the degree of match is "1." The degree of match may be calculated, for example, using the least squares method of the error (residual).

[0122] Fig. 19 is a graph showing an example of the results of fitting performed in step S62 of Fig. 15. Fig. 19(A) shows an example of the analysis results from the first fitting. In the analysis results shown in Fig. 19(A), the degree of match is 0.951.

[0123] A new wavelength table f(λ) is created by updating the coefficients and intercepts of the current wavelength table f(λ). Note that the new wavelength table f(λ) is created so as not to deviate from the emission line positions of the light source used in the measurement in step S52.

[0124] Fig. 19(B) shows an example of the analysis results from the second fitting. In the analysis results shown in Fig. 19(B), the degree of agreement has improved to 0.952.

[0125] By repeating the updating of the wavelength table f(λ) and fitting the thickness of the air gap 58, the wavelength table f(λ) that maximizes the degree of agreement is searched for.

[0126] Figure 19(C) shows an example of the final analysis result obtained by fitting. In the analysis result shown in Figure 19(C), the degree of agreement has improved to 0.955. At this time, the thickness of the air gap 58 of the calibration sample 50 was calculated to be 19.802014 μm.

[0127] FIG. 20 is an example of a spectral spectrum calculated by a wavelength table f(λ) determined by the second wavelength calibration method shown in FIG. 15.

[0128] In the second wavelength calibration method, with known emission line positions as constraint conditions, the wavelength table f(λ) is sequentially updated, and the spectral spectrum (measurement waveform) calculated based on each wavelength table f(λ) and the simulation waveform calculated based on the model of the calibration sample 50 are made to match. The thickness of the air gap 58 of the calibration sample 50 is fitted. Finally, the wavelength table f(λ) for which the spectral spectrum (measurement waveform) and the simulation waveform match most closely is determined as the result of wavelength calibration.

[0129] As described above, the thickness of the air gap 58 of the calibration sample 50 does not need to be known. The thickness of the air gap 58 may be determined from the simulation result when the wavelength table is determined.

[0130] Also, as described above, although the refractive index of the air gap 58 depends on the environment, the influence on the determined wavelength table can be ignored.

[0131] <E. Wavelength Calibration Method When No Emission Line Spectrum Exists (Third Wavelength Calibration Method)> Next, a wavelength calibration method (third wavelength calibration method) when no emission line spectrum exists within the measurement wavelength range will be described. In the third wavelength calibration method, the analysis result of the second wavelength calibration method is used.

[0132] For example, in the spectroscope 1 to which wavelengths have been assigned by a previously executed wavelength calibration method, the diffraction grating 14 is rotated to change the relative positional relationship with respect to the collimating mirror 12 and the focusing mirror 16. Assume that due to the rotation of the diffraction grating 14, the wavelength range of the light incident on the detector 18 is changed from 505 to 550 nm to 450 to 495 nm (more precisely, 448.8297 nm to 496.9859 nm). Assume that the measurement system 100 shown in FIG. 5 is maintained.

[0133] By first performing the wavelength calibration method, the thickness of the air gap 58 of the calibration sample 50 (and the optical distance calculated by multiplying the thickness by the refractive index) becomes known. Using the known thickness of the air gap 58, an accurate simulation waveform can be calculated. The coefficients and intercepts of the wavelength table are fitted so that the optical spectrum (measured waveform) calculated using the wavelength table from the measurement results matches the calculated simulation waveform. By determining the wavelength table through such fitting, wavelength calibration can be achieved even for measurement wavelength ranges where no emission line spectrum exists.

[0134] Fig. 21 is a flowchart showing an example of a processing procedure of the third wavelength calibration method according to the present embodiment. It is assumed that the second wavelength calibration method shown in Fig. 15 has been executed prior to execution of the third wavelength calibration method of Fig. 21.

[0135] 21, for the spectrometer 1 on which the second wavelength calibration method has been executed, a change is made to rotate the diffraction grating 14 (step S80). That is, the positional relationship of the diffraction grating 14 of the spectrometer 1 is changed. Next, based on the design values ​​of the spectrometer 1 after the change, a wavelength table f0(λ) is calculated (step S82). The calculated wavelength table f0(λ) is set as the current wavelength table f(λ).

[0136] The calculation of the wavelength table f0(λ) in step S82 may be performed at any timing.

[0137] 5 (including the modified detector 18), the calibration sample 50 is measured (step S84). That is, the reflected light (or transmitted light) generated by irradiating the calibration sample 50 with light is applied to the spectrometer 1 in which the positional relationship of the diffraction grating 14 has been modified, and a measurement result (third measurement result) output from the detector 18 is obtained.

[0138] The measurement in step S84 is performed using the same optical system and calibration sample 50 as in the previously performed measurement in the second wavelength calibration method. The measurement result in step S84 indicates the change in reflectance for each pixel number (imaging position λ) of the detector 18.

[0139] Subsequently, the wavelength table is repeatedly updated (steps S86 to S92) so as to minimize the error calculated based on the measurement result (third measurement result) in step S84 and the wavelength table.

[0140] Based on the analysis result (thickness of air gap 58) of the previously executed second wavelength calibration method, a simulation waveform showing an interference waveform generated by calibration sample 50 is calculated using the current wavelength table f(λ) (step S86). Also, using the current wavelength table f(λ), an optical spectrum showing the interference waveform is calculated from the measurement result of step S84 (step S88). The calculations in step S86 and step S88 may be performed in either order.

[0141] The degree of match between the simulation waveform calculated in step S86 and the spectrum (interference waveform) calculated in step S88 is calculated (step S90). The calculated degree of match and the wavelength table are recorded in association with each other (step S92).

[0142] It is determined whether or not a termination condition is met (step S94). The termination condition may include, for example, that the calculation of the degree of match has been performed a predetermined number of times.

[0143] If the termination condition is not met (NO in step S94), the coefficients and intercepts of the current wavelength table f(λ) are updated (step S96), and the processes from step S86 onwards are repeated.

[0144] If the termination condition is met (YES in step S94), the wavelength table with the highest degree of coincidence among the performed fittings is output as the result of wavelength calibration (step S98).

[0145] In this way, in the third wavelength calibration method, the wavelength table f(λ) is repeatedly updated so as to minimize the error between the waveform calculated from the measurement result (third measurement result) in step S84 using the wavelength table f(λ) and the simulation waveform calculated based on the model of the calibration sample 50 in which the previously determined thickness of the air gap 58 is fixed.

[0146] 22 and 23 are graphs showing a processing example of the third wavelength calibration method according to the present embodiment, based on the analysis result that the thickness of the air gap is 19.802014 μm.

[0147] Fig. 22(A) shows an example of the first fitting result, and Fig. 22(B) shows an enlarged waveform of the central part of the fitting result shown in Fig. 22(A).

[0148] The fitting result shown in Figure 22 shows a degree of agreement of 0.867. It can be seen that the spectrum calculated using the current wavelength table is shifted to the short wavelength side compared to the simulation waveform.

[0149] Fig. 23(A) shows an example of the second fitting result. In the fitting result shown in Fig. 23(A), it can be seen that the degree of match has improved to 0.918.

[0150] 23(B) shows an example of the final fitting result. In this example, the maximum degree of match is 0.953. The wavelength table with the maximum degree of match is determined to be the most likely wavelength table.

[0151] FIG. 24 is an example of a spectroscopic spectrum calculated by a wavelength table f(λ) determined by the third wavelength calibration method shown in FIG. 21.

[0152] In the above-described third wavelength calibration method, an optimal wavelength table applied to the measurement result of the calibration sample 50 is determined based on a simulation waveform calculated using the thickness of the air gap 58 of the calibration sample 50 determined in the previously executed wavelength calibration method. By acting such a method, wavelength calibration can be performed even when there is no emission line spectrum within the measurement wavelength range.

[0153] <Configuration Example of Information Processing Apparatus 200> At least part of the processing of the above-described wavelength calibration method may be executed in the information processing apparatus 200.

[0154] FIG. 25 is a schematic diagram showing a configuration example of an information processing apparatus 200 for executing the wavelength calibration method according to the present embodiment. Referring to FIG. 25, the information processing apparatus 200 includes a processor 202, a main memory 204, an input unit 206, a display unit 208, a storage 210, a local communication interface 220, a host communication interface 222, and a media drive 224.

[0155] The processor 202 is typically an arithmetic processing unit such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), and reads and executes one or more programs stored in the storage 210 into the main memory 204. The main memory 204 is a volatile memory such as a DRAM (Dynamic Random Access Memory) or an SRAM (Static Random Access Memory), and functions as a working memory for the processor 202 to execute programs.

[0156] The input unit 206 includes a keyboard, a mouse, etc., and receives operations from the user. The display unit 208 outputs the results of program execution by the processor 202 to the user.

[0157] The storage 210 is made up of a nonvolatile memory such as a hard disk or flash memory, and stores various programs and data. More specifically, the storage 210 holds an operating system 212 (OS), a wavelength calibration program 214, measurement results 216, and a wavelength table 218 (wavelength table 22).

[0158] The operating system 212 provides an environment in which the processor 202 executes programs. The wavelength calibration program 214 is executed by the processor 202 to wavelength-calibrate the spectrometer 1. That is, the wavelength calibration program 214 includes computer-readable instructions for executing processes required for the wavelength calibration method according to the present embodiment. More specifically, the wavelength calibration program 214 may include computer-readable instructions for executing at least some of the steps of the processing procedure shown in FIG. 8, at least some of the steps of the processing procedure shown in FIG. 15, and at least some of the steps of the processing procedure shown in FIG. 21.

[0159] The measurement result 216 includes data output from the spectrometer 1. The wavelength table 218 is output by executing the wavelength calibration program 214.

[0160] The local communication interface 220 mediates data transmission between the information processing device 200 and the spectrometer 1 .

[0161] The upper communication interface 222 mediates data transmission between any personal computer or the like.

[0162] The media drive 224 reads necessary data from a recording medium 226 (for example, an optical disk) that stores programs to be executed by the processor 202, and stores the data in the storage 210. The wavelength calibration program 214 to be executed in the information processing device 200 may be installed via the recording medium 226, or may be downloaded from a server device via the upper communication interface 222.

[0163] The wavelength calibration program 214 may execute processing by calling necessary modules in a predetermined sequence at a predetermined timing among the program modules provided as part of the operating system 212. In such a case, a wavelength calibration program 214 that does not include such modules is also included in the technical scope of the present invention. The wavelength calibration program 214 may be provided as being incorporated into a part of another program.

[0164] In this specification, the term "processor" includes a CPU, a GPU, and a hardwired logic circuit (for example, a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC)).

[0165] Instead of the information processing device 200 performing all the necessary processes, the processes may be shared among a plurality of information processing devices, or some of the processes may be handled by the spectrometer 1. Furthermore, computing resources (so-called cloud) on a network (not shown) may be configured to perform all or some of the necessary processes.

[0166] <G.まとめ> When multiple emission line spectra exist within the measurement wavelength range, accurate wavelength calibration is possible, but when there are few emission line spectra within the measurement wavelength range, the accuracy of wavelength calibration may decrease. In a polychromator spectrometer that uses a diffraction grating as the dispersive optical element, the dispersion characteristics can be defined by a trigonometric function, so wavelength calibration is possible as long as two emission line spectra exist within the measurement wavelength range.

[0167] However, in a high-resolution spectrometer, there may be cases where only one emission line spectrum exists within the measurement wavelength range, or where no emission line spectrum exists at all. In such cases, there is a problem that it is not possible to create a wavelength table.

[0168] For transmittance meters and reflectance meters, multi-order light such as second-order light and third-order light can be used for wavelength calibration by providing an order separation filter to the light source. However, in a polychromator spectrometer capable of measuring a light source, an order separation filter must be provided inside the spectrometer, which poses a restriction that an additional configuration such as a filter switching mechanism is required.

[0169] In this embodiment, by measuring the interference waveform using a calibration sample with an internal gap (air gap or vacuum gap), wavelength calibration can be achieved with high accuracy even when there is only one emission line spectrum within the measurement wavelength range.

[0170] In particular, if the polychromator has high resolution (a relatively narrow measurement wavelength range), the refractive index of air can be considered uniform over the measurement wavelength range, so the refractive index when an air gap is used can be calculated by fixing it to 1.

[0171] Furthermore, by accurately determining the thickness of the gap in the calibration sample, it is possible to achieve wavelength calibration for a polychromator spectrometer having an arbitrary measurement wavelength range using the same calibration sample.

[0172] In this embodiment, a calibration sample having an internal gap is used, so that a known standard sample is not required, and temperature control is also not required.

[0173] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0174] 1 Polychromator spectrometer (spectroscope), 2 Sample light, 4, 80 Spectroscopic spectrum, 10 Slit, 12 Collimating mirror, 14 Diffraction grating, 16 Focus mirror, 18 Detector, 20 Processing section, 22, 218 Wavelength table, 30 Light source, 40 Y-shaped fiber, 41, 43 End, 42 Light emitting and receiving probe, 50 Calibration sample, 51, 55 Anti-reflection coating, 52, 54 Quartz plate, 53 Shim, 56 Air hole, 58 Air gap, 82 Short wavelength waveform, 84 Medium wavelength waveform, 86 Long wavelength waveform, 100 Measurement system, 200 Information processing device, 202 Processor, 204 Main memory, 206 Input section, 208 Display section, 210 Storage, 212 Operating system, 214 Wavelength calibration program, 216 Measurement results, 220 Local communication interface, 222 Upper communication interface, 224 media drive, 226 recording medium.

Claims

1. A wavelength calibration method for a polychromator spectrometer having a diffraction grating and a detector on which light dispersed by the diffraction grating is imaged, comprising the steps of: applying light having a known emission line spectrum to the polychromator spectrometer and obtaining a first measurement result output from the detector; irradiating a calibration sample having a gap therein with light, and providing the resulting reflected or transmitted light to the polychromator spectrometer to obtain a second measurement result output from the detector; determining a wavelength table so that a position of the known emission line spectrum in the first measurement result coincides with a wavelength of the known emission line spectrum, the wavelength table indicating a correspondence relationship between an output of the detector and a wavelength; A wavelength calibration method comprising the step of repeatedly updating the wavelength table so as to minimize an error calculated based on the second measurement result and the wavelength table.

2. 2. The wavelength calibration method according to claim 1, wherein the error includes an error between power spectra calculated from each waveform obtained by dividing the waveform calculated from the second measurement result using the wavelength table by wavelength.

3. 2. The wavelength calibration method according to claim 1, wherein the error includes an error between a waveform calculated from the second measurement result using the wavelength table and a simulation waveform calculated based on a model of the calibration sample.

4. 4. The wavelength calibration method of claim 3, further comprising determining a gap thickness of the calibration sample when the error is minimized.

5. changing the positional relationship of the diffraction grating of the polychromator; a step of applying reflected or transmitted light generated by irradiating the calibration sample with light to a polychromator spectrometer in which the positional relationship of the diffraction grating has been changed, and acquiring a third measurement result output from the detector; 5. The wavelength calibration method according to claim 4, further comprising the step of repeatedly updating the wavelength table so as to minimize an error between a waveform calculated from the third measurement result using the wavelength table and a simulation waveform calculated based on a model of the calibration sample in which the determined gap thickness is fixed.

6. 6. The wavelength calibration method according to claim 1, wherein the step of repeatedly updating the wavelength table includes a step of maintaining a wavelength of an emission line spectrum in an optical spectrum calculated from the first measurement result using the updated wavelength table to match a wavelength of the known emission line spectrum.

7. A calibration sample used in the wavelength calibration method according to any one of claims 1 to 5.

8. A wavelength calibration program for wavelength calibrating a polychromator spectrometer including a diffraction grating and a detector on which light dispersed by the diffraction grating is imaged, the wavelength calibration program being programmed into a computer to: obtaining a first measurement result output from the detector when light having a known emission line spectrum is applied to the polychromator spectrometer; acquiring a second measurement result output from the detector when the polychromator spectrometer is provided with reflected or transmitted light generated by irradiating a calibration sample having a gap therein with light; determining a wavelength table so that the position of the known emission line spectrum in the first measurement result coincides with the wavelength of the known emission line spectrum, the wavelength table indicating a correspondence relationship between the output of the detector and a wavelength; and a wavelength calibration program that executes a step of repeatedly updating the wavelength table so as to minimize an error calculated based on the second measurement result and the wavelength table;

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