Far-infrared spectroscopic device and far-infrared spectroscopic method

Abstract

This far-infrared analyzing device comprises: a holding mechanism configured to be capable of holding a specimen in moist air; a detector for detecting light obtained by emitting a far-infrared light beam onto the specimen; and a signal processing unit for computing an absorption spectrum of the specimen from a signal from the detector. The signal processing unit acquires: a first spectrum detected by the detector when the far-infrared light beam is emitted along a measurement optical path while the wavelength of the far-infrared light beam is changed, without the specimen being on the measurement optical path; and a second spectrum detected by the detector when the far-infrared light beam is emitted along the measurement optical path while the wavelength of the far-infrared light beam is changed, with the specimen on the measurement optical path. Then, a difference between the spectrum signals is calculated at frequency intervals determined in accordance with an absorption peak due to water vapor, and the frequency of the absorption peak due to water vapor is selected in accordance with a comparison between the difference and a threshold. Data removal is performed for the spectrum signals on the basis of the selected frequency.

Description

[Technical Field]

[0001] The present invention relates to a far-infrared spectroscopic device and a far-infrared spectroscopic method. [Background technology]

[0002] Far-infrared light in the 0.1 THz to 10 THz range is also known as terahertz waves. This frequency band is intermediate between radio waves and light, and terahertz waves are characterized by the straightness of light and their high transparency. Furthermore, because terahertz waves have energy equivalent to the excitation width of phonon modes, absorption peaks derived from lattice vibrations and intermolecular vibrations can be obtained.

[0003] This absorption peak can be observed at a frequency specific to a substance, and is therefore used for non-destructive substance identification, etc. Utilizing the above characteristics, it is expected that this will also be applied to industrial applications such as imaging technology and quantitative analysis of components, including the inspection of hazardous materials and pharmaceuticals.

[0004] One of the terahertz spectroscopy methods is terahertz time domain spectroscopy (THz-TDS), which has been in practical use since the 1990s and has since become common. This THz-TDS method uses a femtolaser as a light source to acquire the time waveform of a broadband terahertz pulse. The absorption spectrum can be obtained by performing a fast Fourier transform on this time waveform.

[0005] In the field of pharmaceutical testing, research and development is progressing on destructive and non-destructive testing of pharmaceuticals using infrared light, ultraviolet light, Raman scattered light, terahertz waves, etc. In particular, research and development is progressing to support in-line methods in which spectroscopic devices are introduced into the manufacturing process for testing, and expectations are rising for terahertz spectroscopy, which will enable non-destructive testing.

[0006] However, because there are many absorption peaks due to water vapor in the terahertz band, in order to reduce this effect, conventional terahertz spectroscopy requires filling the optical path with a gas such as dry air. This makes it difficult to put in-line pharmaceutical testing into practical use. Furthermore, such humidity changes may cause changes in the crystalline form and properties of the pharmaceutical itself. Therefore, there is a need for a spectroscopic device that can measure samples under wet conditions without using dry air.

[0007] One known method for achieving terahertz spectroscopy under humid conditions is to use data from an existing database of water vapor absorption peak positions to weight and smooth the data for each frequency (Patent Document 1). However, with methods that use information from existing databases, it is difficult to accurately determine frequencies across a sufficient frequency band due to differences in the characteristics of the method used to acquire the database data and the method used to actually measure the spectrum of the sample. Without accurate determination, adjusting the threshold alone would not be enough to reduce the water vapor absorption peak across a sufficient frequency band, posing a challenge to achieving practical performance. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Republished Publication No. 08 / 001785 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention provides a far-infrared spectroscopic device and a far-infrared spectroscopic method that can effectively reduce absorption peaks derived from water vapor with a small amount of calculation, even in any humid air atmosphere, and accurately measure the absorption spectrum derived from a sample. [Means for solving the problem]

[0010] To achieve the above object, the present invention provides a far-infrared analysis device comprising: a holding mechanism configured to hold a sample in humid air; a detector for detecting light obtained by irradiating the sample with far-infrared light; and a signal processor for calculating an absorption spectrum of the sample from a signal from the detector. The signal processor acquires a first spectrum detected by the detector when the far-infrared light is irradiated along the measurement optical path while changing the wavelength of the far-infrared light with the sample not present on the measurement optical path; and a second spectrum detected by the detector when the far-infrared light is irradiated along the measurement optical path while changing the wavelength of the far-infrared light with the sample present on the measurement optical path. The signal processor then calculates a difference between the first spectrum, the second spectrum, or a spectrum obtained based on the first spectrum and the second spectrum at a frequency interval determined according to the width of the absorption peak due to water vapor, compares the difference with a threshold, selects the frequency of the absorption peak due to water vapor, and performs data removal on the signal of the first spectrum, the second spectrum, or the spectrum obtained based on the first spectrum and the second spectrum based on the selected frequency. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a far-infrared spectroscopic device and a far-infrared spectroscopic method that can effectively reduce the influence of absorption peaks derived from water vapor with a small amount of calculation, even in a humid air atmosphere, and accurately measure the absorption spectrum derived from a sample. [Brief explanation of the drawings]

[0012] [Figure 1A] 1 is a schematic diagram illustrating the configuration of a far-infrared spectroscopic device 100 according to a first embodiment. [Figure 1B] This figure shows that when high-intensity pump light with frequency fp is incident on a nonlinear optical crystal with second-order nonlinear susceptibility χ(2), signal light with frequency fs and idler light with frequency fi are parametrically generated. [Figure 1C]1 is a wave number vector diagram showing the momentum conservation law for generating terahertz waves using pump light and seed light. [Figure 1D] FIG. 10 is a diagram showing the relationship between the measurement frequency f and the spectrum intensity value obtained for each frequency. [Figure 2A] FIG. 2 is a diagram illustrating the detailed configuration of a spectrum processing unit 230. [Figure 2B] 10 is a conceptual diagram illustrating a specific example of spectrum removal and interpolation processing in the spectrum removal / interpolation unit 260. FIG. [Figure 2C] FIG. 2 is a block diagram showing a procedure of determination in a water vapor absorption peak frequency determining unit 250 of the far-infrared spectroscopic device of the first embodiment. [Figure 3A] 10 is a graph illustrating a specific example of determining the water vapor absorption peak frequency by calculating the difference dk=r(k+δ)−rk of the reference spectrum and comparing it with a threshold value t. [Figure 3B] 1 is a graph showing an example of a reference spectrum obtained in humid air and a spectrum after removal and interpolation of the water vapor absorption peak. [Figure 4] 1 is a graph showing an example of an absorption spectrum in which the absorption peaks of water vapor and a sample are mixed, and an absorption spectrum of a sample obtained by reducing the influence of the absorption peak of water vapor. [Figure 5] FIG. 10 is a block diagram of a comparative example. [Figure 6A] 10 is a graph showing an example of a reference spectrum acquired at Δ=5 GHz. [Figure 6B] 6B is a graph showing an example of a spectrum obtained by removing, from the reference spectrum of FIG. 6A, intensity values ​​attenuated by the influence of the absorption peak of water vapor. [Figure 6C] FIG. 10 is a block diagram showing an example of the configuration of a water vapor absorption peak frequency determining unit 250b according to a modified example of the first embodiment and a processing procedure. [Figure 7] FIG. 10 is a block diagram showing the processing of a water vapor absorption peak frequency determining unit 250c in the second embodiment. [Figure 8] 10 is a graph showing the results of removing spectral intensity values ​​attenuated by water vapor absorption, based on the second embodiment. [Figure 9] FIG. 10 is a diagram illustrating a process for reducing the influence of water vapor absorption from a sample spectrum, which is executed in the far-infrared spectrometer according to the third embodiment. [Figure 10] FIG. 10 is a diagram illustrating a procedure for reducing the influence of the absorption peak of water vapor from the absorption spectrum of a sample, which is performed in the far-infrared spectroscopic device according to the fourth embodiment. [Figure 11] FIG. 10 is a diagram illustrating details of a water vapor absorption peak frequency determining unit 250d of the far-infrared spectroscopic device according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In the accompanying drawings, functionally identical elements may be denoted by the same numerals. Note that the accompanying drawings show embodiments and implementation examples according to the principles of the present disclosure, but these are for understanding the present disclosure and are not to be used to interpret the present disclosure in a limiting manner. The descriptions in this specification are merely typical examples and are not intended to limit the scope or application of the present disclosure in any way.

[0014] Although the present embodiment has been described in sufficient detail to enable those skilled in the art to practice the present disclosure, it should be understood that other implementations and forms are possible, and that changes in configuration and structure and substitutions of various elements are possible without departing from the scope and spirit of the technical ideas of the present disclosure. Therefore, the following description should not be interpreted as being limited thereto.

[0015] (First embodiment) 1A, the configuration of a far-infrared spectroscopic device 100 according to the first embodiment will be described. As an example, the far-infrared spectroscopic device 100 includes a light source unit 210, an optical system 220, and a spectrum processing unit 230 (signal processing unit). The spectrum processing unit 230 can be configured by a general computer capable of executing various calculations and a computer program for spectrum processing.

[0016] The light source unit 210 and optical system 220 apply a terahertz optical parametric method using an is-TPG (Injection-seeded Terahertz Parametric Generation) light source, which generates high-intensity light (here, terahertz light) from two lights of different wavelengths and a nonlinear optical crystal. The is-TPG method is superior in peak power and wavelength resolution compared to the TDS method described above. Note that, although the following description will be given using an apparatus using an is-TPG light source as an example, the present invention is also applicable to the TDS method.

[0017] Details of the light source unit 210 will be described with reference to Fig. 1A. The light source unit 210 is composed of, for example, a light source 211 as a pump light source, a polarizing beam splitter 212, a light source 213 as a seed light source, optical elements 214 and 215, a mirror 216, etc. The light source unit 210 (is-TPG light source unit) includes light sources 211 and 213 that emit two types of near-infrared light. The two light sources 211 and 213 emit near-infrared light of different wavelengths.

[0018] Light source 211 is a pump light source, and may be, for example, a microchip laser. The light (pump light) emitted from light source 211 is split into two directions by polarizing beam splitter 212, one of which is guided via mirror 216 to nonlinear optical crystal 221a, and the other to nonlinear optical crystal 221b.

[0019] The light source 213 is a seed light source, and may be, for example, a wavelength-tunable semiconductor laser. The optical element 214 is a reflecting mirror whose angle can be controlled, and may be, for example, a galvanometer mirror. The optical element 215 may be, for example, a concave mirror.

[0020] The light (seed light) emitted from light source 213 is incident on nonlinear optical crystal 221a via optical elements 214 and 215. At this time, the incident seed light is guided at an angle (horizontal to the page) that satisfies the phase matching angle, which will be described later, with respect to the pump light, by angle control of optical element 214. At this time, the incident surface of nonlinear optical crystal 221a is in an imaging relationship with the surface of optical element 214, so even if the angle of optical element 214 is changed, the irradiation position of the seed light on the incident surface of nonlinear optical crystal 221a does not change.

[0021] 1A, the optical system 220 is described in detail. The optical system 220 includes, for example, a sealed chamber 229, a near-infrared light detector 225, a control unit 226, a dry air supply unit 227, and a dry air inflow control unit 228.

[0022] Furthermore, a terahertz light generating mechanism made up of nonlinear optical crystal 221a and Si prism 222a pressed together is mounted inside a sample chamber formed by sealed chamber 229. Terahertz light of any wavelength is generated in the terahertz light generating mechanism from pump light incident on nonlinear optical crystal 221a and wavelength-tunable seed light. Note that a beam damper BD1 is provided near nonlinear optical crystal 221a to block unwanted light passing through nonlinear optical crystal 221a.

[0023] Also disposed inside the sample chamber is an optical mechanism in which nonlinear optical crystal 221b and Si prism 222b are pressure-bonded together. Nonlinear optical crystal 221b and Si prism 222b may have the same mechanism (structure) as nonlinear optical crystal 221a and Si prism 222a, and function as a generator of detection light (near-infrared light). Light from Si prism 222a is guided by light-guiding optical system 223 to nonlinear optical crystal 221b via Si prism 222b.

[0024] Furthermore, a sample stage ST and a moving stage RM for holding the sample stage ST are provided near the middle of the nonlinear optical crystals 221a and 221b inside the sample chamber. The sample stage ST, moving stage RM, and sample chamber constitute a holding mechanism for holding the sample in humid air (humid conditions). The sample stage ST and moving stage RM are positioned so that the sample loaded on the sample stage ST can be inserted into and removed from the optical path of the terahertz light described above.

[0025] The principle of generating terahertz light using a nonlinear optical crystal will be described in detail with reference to Figures 1B and 1C. Figure 1B shows the second-order nonlinear susceptibility χ (2) This is a diagram showing that when high-intensity pump light with frequency fp is incident on a nonlinear optical crystal with frequency fp (≠0), signal light with frequency fs and idler light with frequency fi are generated due to nonlinear polarization. In this case, if light with frequency fs is incident simultaneously with the pump light, the light with frequency fi can be amplified (this also holds true if fs and fi are interchanged), and this is called parametric amplification.

[0026] The pump light and seed light are incident non-coaxially on a nonlinear optical crystal, and terahertz waves are generated and amplified by the parametric amplification. The frequencies fpump and fseed of the pump light and seed light are determined to satisfy the following [Equation 1], where fTHz is the frequency of the terahertz light to be generated. In addition, regarding the angle formed by the optical axis of the pump light and the optical axis of the seed light that are incident non-coaxially, when the wave vector of the pump light is expressed as →kpump and the wave vector of the seed light is expressed as →kseed, the wave vector of the generated terahertz wave is → kTHz is determined to satisfy the following [Equation 2].

[0027] [Number 1] fpump-fseed=fTHz [Number 2] →kpump-→kseed=→kTHz

[0028] In FIG. 1A, terahertz light can be parametrically generated by using light from light source 211 and light from seed light source 213 incident on nonlinear optical crystal 221a so that the above-mentioned [Equation 1] and [Equation 2] are satisfied simultaneously.

[0029] 1A is generated based on the same principle as the terahertz light, and near-infrared light is parametrically generated in nonlinear optical crystal 221b using the terahertz light generated from nonlinear optical crystal 221a and the pump light coming from polarized beam splitter 212. The near-infrared light obtained in this way becomes the detection light that enters near-infrared photodetector 225.

[0030] The terahertz light transmitted through the sample placed on the sample stage ST is incident on the nonlinear optical crystal 221b together with the pump light coming from the polarizing beam splitter 212, generating the above-mentioned near-infrared light. This near-infrared light is used as detection light and is guided to the near-infrared light detector 225, where the intensity of the detection light is obtained as a detection signal value.

[0031] When acquiring the absorption spectrum of a sample, the frequency f of the measurement light is changed from the measurement start frequency f1 [THz] to the measurement end frequency f n The frequency is changed in multiple ways at a predetermined frequency interval Δ up to [THz], and the detected signal values ​​are acquired sequentially.

[0032] Figure 1D illustrates this relationship between the acquired signal values. After setting the frequency f of the measurement light to the measurement start frequency f1, first, a detection signal value (reference signal value) x1 is acquired without a sample on the terahertz light path. Next, the sample moving stage RM is moved, the sample is placed on the terahertz light path (sample stage ST), and a detection signal value (sample signal value) y1 is acquired. When multiple samples are measured simultaneously, the detection signal value of the next sample is then acquired. Next, the terahertz light path (measurement light path) is shielded by a light shielding unit (not shown), and detection signal values ​​z1 are acquired sequentially as noise signal values.

[0033] The same process is repeated thereafter. After setting the frequency f of the measurement light to f2, the detection signal values ​​are obtained in the order of the reference signal value x2, the sample signal value y2, and the noise signal value z2 in the same manner as above. This is called the measurement end frequency f n Repeat n times up to this point to obtain the reference signal value xi, the sample signal value yi, and the noise signal value zi (i = 1 to n) at each frequency. As shown in [Equation 3], n indicates the number of acquired data points for the detection signal value, which is determined by the measurement start / end frequencies f1 and fn and the measurement frequency interval Δ.

[0034] [Number 3] n=1+(fn-f1) / Δ

[0035] Regarding the series of detection signals thus obtained (n-th order vector data), the series of signals xi acquired without a sample on the terahertz optical path is used as the reference spectrum (x1, x2, . . . , x n ) is defined as the sample spectrum (y1, y2, . . . , y n ) is defined as the noise spectrum (n1, n2, . . . , n n ) is defined as

[0036] There is also light generated from nonlinear optical crystal 221b that originates only from the pump light, but the influence of light that is generated in this way without depending at all on the terahertz light generated by nonlinear optical crystal 221 is included in the noise spectrum.

[0037] The reference spectrum, the sample spectrum, and the noise spectrum are stored in the control unit 226 and then transmitted to the spectrum processing unit 230. light source( Seed Light Source ) 213, optical element (galvanometer mirror) 214, move The operations of the stage RM, the detector 225, and the dry air inflow control unit 228 can be controlled by a control unit 226.

[0038] The spectrum processing unit 230 calculates the absorption spectrum of the sample based on the reference spectrum, the sample spectrum, and the noise spectrum. The absorption spectrum can be calculated by comparing the sample spectrum with the reference spectrum to determine at what wavelengths and to what extent. Note that the far-infrared spectroscopic device of this embodiment is configured to detect terahertz light transmitted through the sample, but it can also be configured to detect reflected light.

[0039] The configuration of spectrum processing unit 230 is shown in Fig. 2A. Specifically, spectrum processing unit 230 includes a noise processing unit 240, a water vapor absorption peak frequency determination unit 250, a spectrum elimination / interpolation unit 260, and an absorption spectrum calculation unit 270. As shown in Fig. 2A, water vapor absorption peak frequency determination unit 250 further includes a water vapor absorption peak half-width input unit 160, a difference interval calculation unit 165, a difference calculation unit 170, a threshold processing unit 180, and a frequency list storage unit 190. Spectrum elimination / interpolation unit 260 includes spectrum elimination units 261a and 261b and interpolation units 265a and 265b. Each process will be described.

[0040] The noise processing unit 240 has the function of subtracting the noise spectrum from each of the reference spectrum and the sample spectrum (blocks 140a, 140b) to obtain spectra that can be thresholded.

[0041] The water vapor absorption peak frequency determination unit 250 also calculates the water vapor absorption peak frequency by dividing two spectral intensity values ​​x j and x k The function is to calculate the difference value of and perform threshold processing using a threshold value t to identify the frequency affected by the water vapor absorption peak.

[0042] The spectrum removal / interpolation unit 260 also has a function of removing the frequency spectrum extracted by the water vapor absorption peak frequency determination unit 250a from the output of the noise processing unit 240 using spectrum removal units 261a and 261b, and further performing interpolation processing in interpolation units 265a and 265b.

[0043] The absorption spectrum calculation unit 270 has a function of calculating an absorption spectrum based on the reference spectrum and the sample spectrum that have been subjected to spectrum removal / interpolation processing by the spectrum removal / interpolation unit 260 .

[0044] Dry air supply unit 227 is connected to sealed chamber 229 and supplies dry air to the inside of sealed chamber 229. The inflow of dry air is controlled by dry air inflow control unit 228, and the inside of the sealed chamber can be kept in a wet to dry state.

[0045] With reference to FIG. 2A, the detailed configuration of the spectrum processing unit 230 will be described, and a procedure for outputting an absorption spectrum derived from a sample under wet conditions will be described.

[0046] The measurement frequency f is the measurement start frequency f1 [THz] and the measurement end frequency f n [THz], while switching sequentially to the frequencies determined by the frequency interval Δ[THz] (f = (f1, f2, ..., f n )), the reference spectrum, the sample spectrum, and the noise spectrum are obtained. That is, the reference spectrum I0 = (x 1、 x 2、 …, x n ) is set to 110, and the noise spectrum N = (n1, n2, ..., n n ) are set to 120 and input to the noise processing unit 240. In addition, a sample is placed on the terahertz optical path, and the sample spectrum I1=(y1, y2, ..., y n ) is set as 130 and input to the noise processing section 240.

[0047] The noise processing unit 240 subtracts the noise spectrum N from the reference spectrum I0 and the sample spectrum I1 in blocks 140a and 140b, respectively, to obtain spectra R0=(r1, r2, ... r n ), R1=(r'1, r'2, ...r' n ) is obtained.

[0048] [Number 4] r k =x k -n k [Number 5] r' k =y k -n k

[0049] The spectrum R0 obtained by subtracting the noise spectrum N from the reference spectrum I0 is input to the water vapor absorption peak frequency determination unit 250, which performs a determination process (selection process) of the frequency of the absorption peak due to water vapor and stores the determined frequency.

[0050] The water vapor absorption peak full width at half maximum input section 160 is the full width at half maximum δ of the observed water vapor absorption peak. w The difference interval calculation unit 165 calculates the difference interval δ (frequency interval) when calculating the difference for the spectrum R0. As an example, the difference interval δ is the full width at half maximum δ of the absorption peak of water vapor. w For example, the difference interval δ can be calculated based on the following equation: δ×Δ is the full width at half maximum δ w The threshold processing unit 180 determines whether the difference value is larger than the threshold value t, and stores the specific frequency in the frequency list storage unit 190 according to the result. This process will be described in detail later.

[0051] Next, the spectrum removal and interpolation processing executed by the spectrum removal / interpolation unit 260 will be described. As described above, all spectrum intensity values ​​acquired at frequencies stored in the frequency list storage unit 190 are discarded (removed) from spectrum R0 and spectrum R1, leaving them in an uninputted state. Linear interpolation is applied to the spectrum intensity values ​​of the frequencies remaining before and after the uninputted portion (data-removed portion), thereby restoring the discarded spectrum intensity values. This makes it possible to restore a spectrum with reduced water vapor effects.

[0052] A specific example of this spectrum removal and interpolation process will be described with reference to Fig. 2B. In Fig. 2B, the plots of black circles represent the spectrum intensity values ​​acquired at the frequencies stored in the frequency list storage unit 190. The difference value d k is determined to be greater than the threshold value t, the portion is determined to be a spectral frequency of water vapor, and therefore the frequency is stored in the frequency list storage unit 190. Therefore, the data of the intensity values ​​of the black circle plots is discarded, and the removed data is linearly interpolated using the intensity values ​​of the remaining triangular plots, and the white circle plots are restored.

[0053] Next, we will explain the operation of the absorption spectrum calculation unit 270. The absorption spectrum calculation unit 270 includes an absorbance calculation unit 271 and a smoothing processing unit 275. The absorbance calculation unit 271 calculates the absorbance A (absorption spectrum) of the sample to be measured according to the following [Equation 6].

[0054] [Number 6] A=-log 10 (R1 / R0)

[0055] The smoothing processor 275 smooths the spectrum using, for example, a Savitzky-Golay filter or a simple moving average method. The spectrum converted into absorbance is referred to as the absorption spectrum of the sample. Through the above procedure, an absorption spectrum in which the influence of water vapor absorption has been reduced compared to the spectrum acquired under humid conditions can be acquired from the spectrum output unit 280.

[0056] 2C, an example of the process of the water vapor absorption peak frequency determination unit 250 will be described in detail. The difference calculation unit 170 calculates the spectral intensity value r of the spectrum R0 acquired at the kth frequency. (k) and the spectral intensity value r of R0 obtained at the (k+δ)th frequency (k+δ) Difference d k is calculated as shown in [Equation 7].

[0057] [Number 7] d k =r(k+δ) -r (k)

[0058] Here, the difference interval δ is determined by the difference interval calculation unit 165 based on the full width at half maximum δw inputted in the water vapor absorption peak full width at half maximum input unit 160, as described above. The difference interval δ is determined by the following equation: δ×Δ=δ w It is preferable to set the difference interval δ to an approximate integer value that corresponds to a frequency width that is approximately twice the frequency interval Δ. Specifically, the difference interval δ can be determined as shown in [Equation 8], which is expressed using the frequency interval Δ and the INT function (decimals are truncated).

[0059] [Number 8] δ = INT(2δw / Δ + 0.5) (where δ >= 1)

[0060] A threshold value t (t>0) for determining the water vapor absorption peak frequency is input from the threshold value input unit 175. The threshold value processing unit 180 determines whether the threshold value t is larger than the difference dk, and determines (selects) the water vapor absorption peak frequency according to the determination result. Specifically, after the threshold value t is input, the threshold value processing unit 180 executes the threshold determination shown in [Equation 9] and [Equation 10]. By determining the value of the threshold value t based on the minimum amount of attenuation that water vapor absorption has on the spectrum R0, it is possible to accurately extract the frequency at which water vapor absorption is observed.

[0061] [Number 9] d k >t [Number 10] d k <-t

[0062] d k When satisfies [Equation 9], the k-th frequency is determined to be the water vapor absorption peak frequency. k satisfies [Equation 10], the (k+δ)th frequency is determined to be the water vapor absorption peak frequency. The frequency determined to be the water vapor absorption peak frequency is stored in the frequency list storage unit 190. This determination is repeatedly performed from k=1 to k=(n-δ).

[0063] In the far-infrared spectrometer 100, the measurement frequency f is determined, and measurements are performed while increasing the measurement frequency f from the measurement start frequency f1 to the measurement end frequency, thereby acquiring the reference spectrum I0, the sample spectrum I1, and the noise spectrum N. The reference spectrum I0, the sample spectrum I1, and the noise spectrum N can be continuously acquired while keeping the measurement frequency f fixed. Therefore, the water vapor absorption peak frequencies appearing in the reference spectrum I0 and the sample spectrum I1 match for each measurement, even when multiple samples are measured. Therefore, the processing of the water vapor absorption peak frequency determination unit 250a needs to be performed only once for the set of measurements of the reference spectrum I0 and the sample spectrum I1, and does not need to be performed individually.

[0064] 3A and 3B show an example of the first embodiment. In these figures, the measurement start frequency f1 is set to 0.9 THz and the measurement end frequency f n The figure shows the case where the reference spectrum, sample spectrum, and noise spectrum consisting of n = 161 data points were acquired with a frequency of 2.5 THz, a frequency interval Δ of 10 GHz, and a difference interval δ of 1 (equivalent to 10 GHz), and a threshold t of 50.

[0065] Figure 3A shows the difference D of the reference spectrum I0. k =r (k+δ) -r (k) This is a graph plotting the data for each measurement frequency. In Figure 3, the thresholds t = 50 and -50 are shown as straight lines. As a result of the threshold judgment, data acquired at 41 frequencies out of n = 161 were subject to removal and interpolation.

[0066] Figure 3B shows an example of data before and after removing the spectrum of the water vapor absorption peak (spectrum R0 in Figure 2A and spectrum R'0 after spectrum removal and interpolation) according to the water vapor absorption peak frequency identified in Figure 3A. By removing the spectrum attenuated by the influence of water vapor absorption and linearly interpolating that portion, a reference spectrum R0' with reduced influence of water vapor can be obtained.

[0067] Although not shown, the same can be done for the sample spectrum R1. Based on the data acquired as shown in Figure 3A, the spectrum of the water vapor absorption peak is removed and linear interpolation is performed to obtain a spectrum R1' with reduced water vapor absorption.

[0068] The graph on the left side of Figure 4 shows an example of the absorption spectrum of a sample obtained using spectra R0' and R1', in which the influence of the water vapor absorption peak has been reduced. The graph on the right side of Figure 4 shows the spectrum of the same sample output using spectra R0 and R1, in which the influence of the water vapor absorption peak remains. The procedure for outputting the spectrum in the graph on the right side of Figure 4 is as shown in the comparative example in Figure 5. The sharp absorption (indicated by the inverted triangle) that appears due to the influence of water vapor has been reduced in the graph on the left side of Figure 4, and the absorption originating from the sample (indicated by the open inverted triangle) can be clearly observed.

[0069] The operation of the control unit 226 will be described in more detail. light source The wavelength of the tunable laser used in 213 is controlled to generate terahertz waves of any frequency. In order to adjust the change in the optical axis of the seed light (horizontal direction on the paper) that accompanies this wavelength change, the angle (horizontal direction on the paper) of the galvanometer mirror used in optical element 214 is also controlled at the same time. Furthermore, the direction of the optical axis of the terahertz light generated by nonlinear optical crystal 221a changes slightly (horizontal direction on the paper) depending on the frequency. Depending on the amount of change in the direction of the optical axis of this terahertz light (horizontal direction on the paper), control unit 226 move The control unit 226 controls the stage RM. This allows the sample stage ST to be positioned at an appropriate position for each measurement frequency. Furthermore, the control unit 226 controls the opening and closing of the dry air inflow control unit 228 as needed, thereby adjusting the humidity inside the chamber 229 to a level suitable for the sample.

[0070] The difference in the properties of the absorption peaks of water vapor and samples will be discussed. The full width at half maximum of the absorption peak of a solid sample can be observed over a much wider frequency range than that of the absorption peak of water vapor (in the apparatus of this embodiment, the full width at half maximum of the absorption peak of water vapor is approximately 5 GHz, while the absorption of a solid sample is approximately 50 GHz). This broad absorption peak width is thought to be due to collective vibrations of multiple molecules in the solid sample. Therefore, by removing the absorption peak of water vapor, it becomes possible to interpolate the spectrum without significantly impairing the absorption peaks originating from the sample.

[0071] Another specific example of application of the first embodiment (FIG. 2A) is shown below. FIG. 6A shows an example of a reference spectrum consisting of n=401 detection signal values ​​acquired under measurement conditions of measurement start frequency f1=0.87 THz, measurement end frequency fn=2.87 THz, and Δ=5 GHz in a humid environment. Using the method described above, a reference spectrum I0, a sample spectrum I1, and a noise spectrum N are acquired, and spectra R0 and R1 are obtained by subtracting the noise spectrum N from the reference spectrum I0 and the sample spectrum I1. The full width at half maximum of the observed water vapor absorption peak is expressed as δ w = 0.005 THz, so from the above [Equation 8], δ was set to 2. In addition, the threshold value t was set to 50.

[0072] Fig. 6A shows an example of a reference spectrum R0 obtained under the above conditions. Fig. 6B shows an example of a spectrum R0 obtained by excluding data at frequencies stored in frequency list storage unit 190 as a result of threshold determination. It can be seen that the frequencies affected by water vapor absorption were accurately determined, and the influence of the water vapor absorption peak was effectively removed.

[0073] 6C shows a modification of the first embodiment. The water vapor absorption peak frequency determination unit 250 in FIG. 2A calculates one difference d k In contrast to this, in the modified example of FIG. 6C, the difference between the two is calculated, and the water vapor absorption peak frequency is detected according to the result of the threshold value judgment. Specifically, the difference c shown in the following [Equation 11] is calculated.k The difference d k and are simultaneously acquired and subjected to the determination process in the water vapor absorption peak frequency determination unit 250b shown in FIG. 6C. k is the forward difference, c k is a difference defined as a backward difference. In other words, in this modification, the forward difference d is defined as the difference between the signal intensity of the reference spectrum R0 at one frequency and the signal intensity of the reference spectrum R0 at a frequency that is larger than that by an interval Δ. k In addition, the backward difference c is calculated as the difference between the signal intensity of the reference spectrum R0 at one frequency and the signal intensity of the reference spectrum R0 at a frequency that is smaller than that by the interval Δ. k Calculate the difference between the two k , d k When satisfies either of the two conditions in [Equation 12], the signal strength value r k The frequency f k is stored in the frequency list storage unit 190.

[0074] [Number 11] c k =r (k) -r (k-δ) [Number 12] c k <-t or d k >t

[0075] Since ck and d(k-δ) are the same calculation formula, when used with the same difference interval δ, the same frequency as in the example of Figure 2A is obtained at frequency list The data is stored in the storage unit 190. Thereafter, removal and interpolation of data acquired at this frequency can be carried out in the same manner as described above.

[0076] As described above, according to the far-infrared spectroscopic device of the first embodiment, even in an arbitrary humid air atmosphere, it is possible to effectively reduce the absorption peak derived from water vapor with a small amount of calculation, and accurately measure the absorption spectrum derived from the sample.

[0077] (Second embodiment) Next, a far-infrared spectroscopic device according to a second embodiment will be described with reference to FIG. 7. The overall configuration of the device is similar to that of the first embodiment, so a redundant description will be omitted. The far-infrared spectroscopic device of the second embodiment differs from that of the first embodiment in the configuration of the water vapor absorption peak frequency determination unit 250c. According to the second embodiment, the influence of the water vapor absorption peak can be effectively reduced even in frequency regions where the detected light intensity of the reference spectrum is low. The intensity of light obtained by parametric generation exhibits frequency dependence specific to the nonlinear optical crystal used. Therefore, it is conceivable that, within a certain measurement frequency range, there will be frequency bands with low detected light intensity and frequency bands with high intensity.

[0078] The water vapor absorption peak frequency determination unit 250c of the second embodiment includes, in addition to the components of the water vapor absorption peak frequency determination unit 250 of the first embodiment, a difference calculation unit 171 and a threshold input unit 179. The difference calculation unit 171 calculates the difference d k Apart from the threshold t, the difference itself is relativeized with the reference spectrum data as in [Equation 13]. k The threshold input unit 179 inputs a threshold t' that is different from the threshold t. The threshold processing unit 180 then calculates the difference d k In addition to detecting the water vapor absorption peak frequency by comparing with the threshold value t, the relative value difference d k The water vapor absorption peak frequency is detected by comparing ' with a threshold value t'. This makes it possible to detect the water vapor absorption peak even when the signal strength fluctuates within the measurement frequency range. For example, the threshold value t' can be set to 0.25.

[0079] [Number 13] d k '=d k / r k

[0080] difference d k The water vapor absorption peak frequency determined only from the threshold value t matches the frequency of the data removed in Figure 6B. kThe frequency data newly stored in the frequency list storage unit 190 by threshold determination separately performed using ' and threshold t' is shown. The frequency of 1.005 THz, where the intensity of the reference spectrum is low and attenuation due to absorption by water vapor is small, is shown in d k In the second embodiment, the difference d k and the relative value difference d k ' is used in combination with the relative value difference d k It is also possible to adopt a configuration in which the water vapor absorption peak frequency is detected using only the relative value difference d k Even if only ' is used, it is possible to reduce the influence of the water vapor absorption peak in the frequency region where the detected light intensity of the reference spectrum is low, and in this case, the effect can be obtained with simpler processing.

[0081] A modified example of the second embodiment will be described below. In this modified example, instead of the above-mentioned [Equation 11], the ratio of the spectral signal intensities (signal intensity ratio) at different sampling points (for example, adjacent sampling points) is calculated as shown in [Equation 14], and this signal intensity ratio d k The water vapor absorption peak frequency is detected based on the "

[0082] Specifically, in the difference calculation unit 171 of FIG. 7, the signal intensity ratio d k Furthermore, the equations for threshold determination are determined as [Equation 15] and [Equation 16]. When [Equation 15] is satisfied, the (k+δ)th frequency is stored in the frequency list storage unit 190, and when [Equation 16] is satisfied, the kth frequency is stored. The subsequent procedures are the same as those in the second embodiment. According to this modification, it is possible to effectively reduce the influence of the absorption peak of water vapor even in a frequency region where the detected light intensity of the reference spectrum is low. The relative value difference dk' and the signal intensity ratio d k From the relationship, the signal strength ratio d k The modified example in which " is used to determine the water vapor absorption peak frequency is equivalent to the case in which the relative value difference dk' is used.

[0083] [Number 14] dk ”=r k+δ / r k [Number 15] d k "<1-t' [Number 16] d k ”>1+t' [Number 17] dk'=d k / r k =(r k+δ -r k ) / r k =r k+δ / r k -1=d k ''-1

[0084] In addition, the signal strength ratio d k Instead of ", as in the following [Equation 18], r k The difference of the natural logarithm d lnk may also be used.

[0085] [Number 18] d lnk =ln(r k+δ )-ln(r k )=ln(r k+δ / r k )

[0086] [Equation 18] takes the natural logarithm of the ratio of [Equation 14], but since the natural logarithm is a function whose slope can be approximated to 1 in the vicinity of 1, the threshold determination can be made using [Equation 15] and [Equation 16]. In other words, an effect almost equivalent to that obtained when threshold processing is performed on the relative value difference can be obtained.

[0087] (Third embodiment) Next, a far-infrared spectroscopic device according to a third embodiment will be described with reference to FIG. 9. The overall configuration of the device is the same as that of the first embodiment, so a duplicated description will be omitted. The far-infrared spectroscopic device of the third embodiment includes a noise processing unit 240 and a spectrum analyzer. Remove The configuration of the subtraction interpolation unit 260b is different from that of the first embodiment.

[0088] In the water vapor absorption peak frequency determination unit 250 of the first embodiment, the reference spectrum I0 is acquired and the water vapor absorption peak frequency is determined each time a measurement is performed, but in the third embodiment, this procedure is omitted. Remove The interpolation unit 260b also uses the reference spectrum Lu R Targeted at 0 Spectrum The removal unit 261a and the interpolation unit 265a are omitted, Spectrum The subtraction and interpolation operations are performed on the sample spectrum. Lu R Only for 1, Spectrum This is performed by the removal unit 261b and the interpolation unit 265b. That is, in the third embodiment, the sample spectrum including the absorption peak of water vapor is Lu R The spectral data affected by water vapor is removed from the image data 1, and an interpolation operation is performed. The specific procedure will be described below with reference to FIG.

[0089] In this third embodiment, the reference spectrum I0 and noise spectrum N0 are acquired in dry air (under dry conditions) separately from the sample spectrum I1 resulting from the measurement of the sample to be measured, and are input to the noise processing unit 240. When measuring the sample to be measured, the sample is placed on the sample stage ST in moist air, and the sample spectrum I1 and noise spectrum N1 are acquired in the same manner as in the previous embodiments.

[0090] It is desirable that the reference spectrum I0 and noise spectrum N0 are n-th order row vector data acquired at the same measurement start frequency, measurement end frequency, and frequency interval as the sample spectrum I1 and noise spectrum N1. However, it is also possible to use data that meets the following conditions:

[0091] The reference spectrum I0 and the noise spectrum N0 are measured at the measurement start frequency f1' and measurement end frequency f n When the frequencies are acquired at frequency intervals Δ', the order n' of the vector data of the sample spectrum I0 and noise spectrum N0 is determined as shown in the following [Equation 19]. All measured frequencies of the reference spectrum I0 and noise spectrum N0 are expressed as a frequency sequence F' = (f1', f2' ..., f nThe order of the sample spectrum I1 and noise spectrum N1 as vector data is m, and the total measurement frequencies are expressed as a frequency sequence F = (f1, f2, ..., f m ), the reference spectrum I0 and the noise spectrum N0 may be n'-th order vector data acquired at a measurement frequency F' that satisfies [Equation 20].

[0092] [Number 19] n'=1+(f n '-f1') / Δ' [Number 20] n'≧m and F'∋F

[0093] The water vapor absorption peak frequency determination unit 250d performs a water vapor absorption peak frequency determination process on the spectrum R1 obtained by subtracting the noise spectrum N1 from the sample spectrum I1. The configuration of the water vapor absorption peak frequency determination unit 250d itself may be the same as that of the above-described embodiment.

[0094] In the third embodiment, the reference spectrum is Spectrum Since there is no need to simultaneously acquire the reference spectrum, the measurement time can be shortened compared to the first and second embodiments. Furthermore, since the reference spectrum can be acquired in dry air, the reference spectrum data can be used as is without going through the water vapor absorption peak frequency determination unit 250d.

[0095] (Fourth embodiment) Next, a far-infrared spectroscopic device according to a fourth embodiment will be described with reference to Figs. 10 and 11. The overall configuration of the device is the same as that of the first embodiment, so a duplicated description will be omitted. The far-infrared spectroscopic device of the fourth embodiment includes a water vapor absorption peak frequency determining unit 250e and a spectrum Remove The configuration of the subtraction interpolation unit 260c is different from that of the first embodiment.

[0096] In this fourth embodiment, first, a reference spectrum I0, a noise spectrum N0, a sample spectrum I1, and a noise spectrum N1 are acquired and input to a noise processing unit 240. Then, the noise processing unit 240 acquires a reference spectrum R0 and a sample spectrum R1 from which the noise spectra N0 and N1 have been removed, respectively. An absorbance calculation unit 271 calculates the absorption spectrum of the sample using [Equation 6]. The water vapor peak frequency determination unit 250e determines the absorption peak frequency of water vapor from this absorption spectrum. The spectrum is calculated using the determination result. Remove Interpolation section 260 c As in the third embodiment, the reference spectrum I0 and noise spectrum N0 may be acquired in dry air, and the sample spectrum I1 and noise spectrum N1 may be acquired in moist air.

[0097] Details of the determination operation in the water vapor absorption peak frequency determination unit 250e of the fourth embodiment will be described with reference to Fig. 11. This water vapor absorption peak frequency determination unit 250e is configured to obtain the difference in intensity values ​​of the absorption spectrum of the sample, calculated based on the reference spectrum R0 and the sample spectrum R1, and determine the water vapor absorption peak frequency by performing threshold determination similar to the above-described embodiments.

[0098] The difference interval δ is the full width at half maximum of the observed water vapor absorption peak δ w Based on this, it can be determined as in [Equation 8] in the same way as in the above-described embodiment.

[0099] The intensity value of the absorption spectrum of the sample acquired at the kth frequency is a k In this case, the difference calculation unit 171 calculates a k+δ and a k Difference d k The threshold processing unit 181 calculates the difference d k If satisfies [Equation 9], then frequency f k+δ If [Equation 10] is satisfied, the frequency f kare stored in the frequency list storage unit 190.

[0100] [Number 21] d k =a (k+δ) -a (k)

[0101] The intensity value ak of the input absorption spectrum has a sign opposite to that of the sample spectrum A1 (FIG. 11, 141a). Accordingly, the combination of the frequency and the threshold value judgment formula stored (added) in the frequency list storage unit 190 is reversed from that of the threshold processing unit 180 in the first embodiment (d k When t, f k+δ is stored in the frequency list storage unit 190, and d k <-t, fk is stored in the frequency list storage unit 190).

[0102] As shown in FIG. 10, the absorbance values ​​obtained at the frequencies stored in the frequency list storage unit 190 for the absorption spectrum calculated by the absorbance calculation unit 271 are expressed as follows: Spectrum The absorbance value is removed by the removal unit 261a. The removed absorbance value is restored by the interpolation unit 265a by linearly interpolating the absorbance values ​​before and after the removed absorbance value. Furthermore, smoothing is performed as necessary. process A unit 275 performs a smoothing process on the spectrum and outputs the absorption spectrum.

[0103] As described above, according to the device of the fourth embodiment, it is possible to obtain an absorption spectrum A1' in which the influence of water vapor is reduced, using only the absorption spectrum of the sample.

[0104] In the fourth embodiment, there is no need to simultaneously acquire the reference spectrum R0 and the sample spectrum R1, and therefore the measurement time can be shortened compared to the first and second embodiments. Furthermore, because data for which absorbance has already been calculated is handled, it is possible to omit input of the reference spectrum, sample spectrum, and noise spectrum, and to omit processing by the noise processor 240. Furthermore, because processing can be performed without using the reference spectrum, sample spectrum, or noise spectrum, it is possible to reduce the influence of water vapor absorption peaks even when these data are not available.

[0105] The present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0106] 211... Near-infrared light source (pump light), 212... Polarizing beam splitter, 213... Near-infrared light source (seed light), 214, 215... Optical element, 216... Mirror, 221a... Nonlinear optical crystal (terahertz light generating unit), 222a... Si prism (terahertz light generating unit), 221b... Nonlinear optical crystal (detection light generating unit), 222b... Si prism (detection light generating unit), 223... Light guiding optical system, ST... Sample stage, RM... Moving stage, 225... Near-infrared light detector, 226... Control unit, 227... Dry air supply unit, 228... Dry air inflow control unit, 229... Sealed chamber, 230... Spectral processing unit, 240... Noise processing unit, 250... Water vapor absorption peak frequency determination unit, 260... Spectral removal / interpolation unit, 270... Absorption spectrum calculation unit.

Claims

1. a holding mechanism configured to be able to hold a sample in moist air; a detector for detecting light obtained by irradiating the sample with far-infrared light; a signal processing unit that calculates an absorption spectrum of the sample from a signal from the detector; Equipped with The signal processing unit a first spectrum detected by the detector when the far-infrared light is irradiated in the measurement optical path while changing the wavelength of the far-infrared light in a state where the sample is not present on the measurement optical path, and a second spectrum detected by the detector when the far-infrared light is irradiated in the measurement optical path while changing the wavelength of the far-infrared light in a state where the sample is present on the measurement optical path, calculating a difference for each frequency interval determined in accordance with a width of an absorption peak due to water vapor for any one of the first spectrum, the second spectrum, or a spectrum obtained based on the first spectrum and the second spectrum, and selecting a frequency of the absorption peak due to water vapor in accordance with a comparison between the difference and a threshold value; performing data removal based on the selected frequencies; restoring the data of the portion from which the data has been removed by performing interpolation based on the remaining data before and after the portion from which the data has been removed; The signal processing unit performs the data removal by: performing the data removal on the first spectrum, or performing the data removal on the second spectrum while acquiring the first spectrum under dry conditions when acquiring the first spectrum, instead of performing the data removal on the first spectrum; or A signal having a spectrum obtained based on the first spectrum and the second spectrum is subjected to A far-infrared spectroscopic device characterized by:

2. the signal processing unit acquires a noise spectrum obtained by performing a measurement while blocking the measurement optical path; 2. The far-infrared spectroscopic device according to claim 1, further comprising: subtracting a noise spectrum from the first spectrum and the second spectrum; and performing data removal on the first spectrum or the second spectrum after the subtraction.

3. the signal processing unit sets the measurement optical path under a wet condition and acquires the first spectrum and the second spectrum; 2. The far-infrared spectroscopic device according to claim 1, configured to select a frequency of an absorption peak due to water vapor based on the difference of the first spectrum.

4. the signal processing unit sets the measurement optical path to a dry condition and acquires the first spectrum; 2. The far-infrared spectroscopic device according to claim 1, configured to select a frequency of an absorption peak due to water vapor based on the difference of the second spectrum.

5. The signal processing unit may obtain the difference as a forward difference, which is the difference between the signal strength of the spectrum at one frequency and the signal strength of the spectrum at a frequency greater than that frequency; a backward difference, which is the difference between the signal strength of the spectrum at a frequency and the signal strength of the spectrum at a frequency lower than that frequency; and comparing the forward difference and the backward difference with the threshold value to select a frequency of the absorption peak due to the water vapor.

6. 2. The far-infrared spectroscopic device according to claim 1, wherein the signal processing unit is configured to use, as the difference, a difference obtained by relative-value-calculating the difference of the spectral signals with the signal value of the spectrum, and to select a frequency of an absorption peak due to water vapor.

7. 2. The far-infrared spectroscopic device according to claim 1, wherein the signal processing unit is configured to select a frequency of an absorption peak due to water vapor based on a difference between a spectrum obtained based on the first spectrum and the second spectrum.

8. 2. The far-infrared spectroscopic device according to claim 1, further comprising: a dry air supply unit that supplies dry air into the sample chamber containing the sample; and a dry air inflow control unit that controls the inflow of the dry air.

9. acquiring a first spectrum detected by a detector when far-infrared light is irradiated onto the measurement optical path while changing the wavelength of the far-infrared light in a state where a sample is not present on the measurement optical path, and a second spectrum detected by the detector when far-infrared light is irradiated onto the measurement optical path while changing the wavelength of the far-infrared light in a state where the sample is present on the measurement optical path; calculating a difference for each frequency interval determined according to a width of an absorption peak due to water vapor for any one of the first spectrum, the second spectrum, and a spectrum obtained based on the first spectrum and the second spectrum, and selecting a frequency of the absorption peak due to water vapor according to a comparison between the difference and a threshold value; performing data removal based on the selected frequencies; restoring data from the portion from which data has been removed by performing interpolation based on remaining data before and after the portion from which data has been removed; Including, The step of performing the data removal comprises: performing the data removal on the first spectrum, or performing the data removal on the second spectrum while acquiring the first spectrum under dry conditions when acquiring the first spectrum, instead of performing the data removal on the first spectrum; or performing on a signal having a spectrum obtained based on the first spectrum and the second spectrum; Far infrared spectroscopy method.

10. 10. The far-infrared spectroscopy method according to claim 9, further comprising: acquiring a noise spectrum obtained by performing measurement while blocking the measurement optical path; subtracting the noise spectrum from the first spectrum and the second spectrum; and performing data removal on the first spectrum or the second spectrum after the subtraction.

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