Spectrophotometer

Abstract

To improve accuracy of control of an amount of light from an infrared light source in a spectrophotometer comprising the infrared light source.SOLUTION: A spectrophotometer comprises an infrared light source 10, an interferometer, a first detector, and a monitor unit. The monitor unit 1 monitors an output of the infrared light source 10. The monitor unit 1 includes a second detector 11 and a light amount control unit 12. The second detector 11 outputs a signal in accordance with an amount of output light. The light amount control unit 12 can perform such operation that the infrared light source 10 is controlled on the basis of the signal in order for the amount to approach a target amount of light. The infrared light source 10 outputs light having a first wavelength range and light having a second wavelength range different from the first wavelength range. The second detector 11 includes a first photodetection element 111 and a second photodetection element 112. The first photodetection element 111 outputs a first voltage VB in accordance with the light having the first wavelength range to the light amount control unit. The second photodetection element 112 outputs a second voltage VG in accordance with the light having the second wavelength range to the light amount control unit 12.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to spectrophotometers that include an infrared light source, and more particularly to controlling the infrared light source. [Background technology]

[0002] Conventionally, spectrophotometers equipped with an infrared light source are known. For example, U.S. Patent No. 7,119,904 (Patent Document 1) discloses a Fourier transform infrared (FTIR) spectrophotometer equipped with a photodetector that outputs a signal according to the amount of light emitted from the infrared light source. In this spectrophotometer, feedback control is performed on the infrared light source based on the voltage difference between the voltage output from the photodetector and a target voltage so that the amount of light emitted from the infrared light source is constant at a target light amount. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 7,119,904 Summary of the Invention [Problem to be solved by the invention]

[0004] In the spectrophotometer disclosed in Patent Document 1, a laser beam is emitted to an interferometer to control the interferometer including a moving mirror. Due to multiple reflection or scattering of the laser beam in the interferometer, a part of the laser beam may reach the photodetector. In addition, the physical properties of the components of the photodetector usually have temperature characteristics. Even if the amount of infrared light emitted from the infrared light source is the same, the laser beam and the temperature characteristics may become disturbances, and the voltage output from the photodetector may change. Therefore, the actual light amount difference between the amount of light emitted from the infrared light source and the target light amount may deviate from the light amount difference corresponding to the voltage difference between the voltage output from the photodetector that received the light and the target voltage. As a result, it may be difficult to bring the amount of light emitted from the infrared light source close to the target light amount by feedback control based on the voltage difference.

[0005] The present invention has been made to solve the above problems, and an object of the present invention is to improve the accuracy of light amount control of an infrared light source in a spectrophotometer equipped with the infrared light source. [Means for solving the problem]

[0006] The spectrophotometer according to the present invention includes an infrared light source, an interferometer, a first detector, and a monitor unit. The infrared light source emits output light including light in an infrared wavelength range. The interferometer generates interference light based on the input output light. The first detector detects light generated based on the interference light output from the interferometer and transmitted through or reflected by the sample. The monitor unit monitors the output of the infrared light source. The monitor unit includes a second detector and a light amount control unit. The second detector outputs a signal according to the amount of the output light. The light amount control unit is operable to control the infrared light source based on the signal so that the amount approaches a target light amount. The infrared light source emits light in a first wavelength range and light in a second wavelength range different from the first wavelength range. The second detector includes a first light detection element and a second light detection element. The first light detection element outputs a first voltage according to the light in the first wavelength range to the light amount control unit. The second light detection element outputs a second voltage corresponding to the light in the second wavelength range to the light amount control unit. Effect of the Invention

[0007] According to the spectrophotometer of the present invention, a first voltage corresponding to light in a first wavelength range and a second voltage corresponding to light in a second wavelength range are output from the second detector to the light amount control unit, thereby improving the accuracy of light amount control of the infrared light source. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an FTIR as an example of a spectrophotometer according to an embodiment. [Diagram 2] This is the spectrum of radiation emitted from an infrared light source. [Diagram 3] 11 is a diagram showing a configuration of a photodetector and a light amount control unit according to a comparative example. FIG. [Figure 4] 3 is a diagram illustrating a configuration of a light detector and a light amount control unit according to the embodiment. FIG. [Diagram 5] 5 is a spectrum showing a sensitivity wavelength range of a photodetection element included in the photodetector of FIG. 4. [Figure 6] FIG. 13 is a diagram showing a configuration of a photodetector according to a first modified example of the embodiment. [Figure 7] FIG. 13 is a diagram showing a configuration of a photodetector according to a second modified example of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiment will be described in detail with reference to the drawings. In the following, the same or corresponding parts in the drawings are given the same reference characters, and in principle, the description thereof will not be repeated. In the following, a Fourier transform infrared spectrophotometer will be simply referred to as FTIR.

[0010] Fig. 1 is a schematic diagram of an FTIR 100, which is an example of a spectrophotometer according to an embodiment. In Fig. 1, the X-axis, the Y-axis, and the Z-axis are perpendicular to each other.

[0011] As shown in FIG. 1, the FTIR 100 includes an infrared light source 10, a monitor unit 1, a collimating mirror 21, mirrors 22 and 23, an interferometer 3, a sample chamber 4, a photodetector 5 (first detector), a laser light source 6 (monochromatic light source), a photodetector 60, and mirrors 61, 62, and 63.

[0012] The infrared light source 10 emits light including light in the infrared wavelength range (infrared light). The monitor unit 1 includes a photodetector 11 (second detector) and a light amount control unit 12. The monitor unit 1 monitors the output of the infrared light source 10.

[0013] The interferometer 3 generates infrared interference light based on the emitted light input from the infrared light source 10. The interferometer 3 is, for example, a Michelson type interferometer, and includes a movable mirror 31, a beam splitter (half mirror) 32, and a fixed mirror 33. The movable mirror 31 has a drive mechanism and is capable of moving linearly in the X-axis direction. The fixed mirror 33 is configured to be rotatable about a rotation axis parallel to the Z-axis, and the rotation angle is controlled so as to follow the movement of the movable mirror 31.

[0014] A sample 40 is placed in the sample chamber 4. In the FTIR 100, infrared light emitted from the infrared light source 10 is guided to the interferometer 3, and the infrared interference light from the interferometer 3 is guided to the photodetector 5 via the sample 40. The photodetector 5 detects light generated based on the infrared interference light transmitted through the sample 40. The FTIR 100 may be configured such that the photodetector 5 detects light generated based on the infrared interference light reflected by the sample 40.

[0015] The FTIR 100 receives signals from the photodetectors 5 and 60 and performs analysis, and also includes a control device (not shown) that performs overall control of the FTIR 100. The light amount control unit 12 may be formed as a part of the control device.

[0016] The infrared light source 10 is, for example, a Glober light source, which is a thermal light source that utilizes blackbody radiation from a high-temperature infrared element. The infrared element is formed by embedding a heating wire in a ceramic such as SiC or SiN, for example. When an electric current flows through the infrared element, the infrared element is heated to 1000K to 1500K, and radiation light (emitted light) including infrared light is generated from the infrared element and emitted from the infrared light source 10. The intensity (radiation spectrum) B(λ,T) of light with wavelength λ generated from the infrared element at temperature T is represented by Planck's radiation formula shown in the following formula (1). In formula (1), h is Planck's constant, c is the speed of light, and k is Boltzmann's constant.

[0017] [Number]

[0018] Figure 2 is the spectrum of the radiation light emitted from the infrared light source 10. In Figure 2, curve C11 represents the radiation spectrum B(λ,T1) at temperature T1. Curve C12 represents the radiation spectrum B(λ,T2) (<T1) at temperature T2. Curve C13 represents the radiation spectrum B(λ,T3) (<T2) at temperature T3. As shown in Figure 2, each of the radiation spectra B(λ,T1) to B(λ,T3) has a peak (maximum value) in the wavelength range of 2μm to 3μm included in the infrared region (0.78μm to 1000μm).

[0019] Note that the infrared light source may be switched according to the wavelength range of the infrared light used for analysis. For example, when the wavelength range is the near-infrared region (0.78μm to 2μm), the infrared light source may be switched to a halogen light source, and when the wavelength range is the mid-infrared region (2μm to 4μm) and the far-infrared region (4μm to 1000μm), the infrared light source may be switched to a ceramic light source.

[0020] 1 again, the photodetector 11 receives radiant light emitted from the infrared light source 10 and outputs a signal corresponding to the amount of the radiant light to the light amount control unit 12. The light amount control unit 12 is operable to perform feedback control on the infrared light source 10 based on the signal so that the amount of radiant light emitted from the infrared light source 10 approaches a target light amount.

[0021] The infrared light emitted from the infrared light source 10 as a diverging light beam is converted by the collimating mirror 21 into a parallel light beam (collimated light) and guided to the beam splitter 32. The infrared light emitted from the infrared light source 10 may be converged and then guided to the collimating mirror 21 via an aperture.

[0022] The infrared light guided to the beam splitter 32 is split by the beam splitter 32 into infrared light directed toward the movable mirror 31 and infrared light directed toward the fixed mirror 33. The reflected light from the movable mirror 31 and the reflected light from the fixed mirror 33 interfere with each other at the beam splitter 32, causing infrared interference light to be output from the interferometer 3. The intensity (amplitude) of the infrared interference light changes as the movable mirror 31 moves.

[0023] The laser light source 6 emits a HeNe laser beam (monochromatic light) for controlling the interferometer 3. The wavelength of the HeNe laser beam is 632.8 nm. The HeNe laser beam emitted from the laser light source 6 passes through a mirror 61, and is then reflected by mirrors 62 and 63 and guided to the beam splitter 32. The HeNe laser beam guided to the beam splitter 32 is split by the beam splitter 32 into a HeNe laser beam directed toward the movable mirror 31 and a HeNe laser beam directed toward the fixed mirror 33. The reflected beam from the movable mirror 31 and the reflected beam from the fixed mirror 33 interfere with each other at the beam splitter 32, thereby generating laser interference beams. The laser interference beam from the beam splitter 32 is guided to the photodetector 60 by the mirrors 63, 62, and 61. When the movable mirror 31 moves at a constant speed, the intensity of the laser interference beam is detected as a laser beam interference fringe signal, which is a sine wave of a constant frequency. Based on the interference fringe signal, the position and speed of movable mirror 31 and the angle of fixed mirror 33 are controlled. Note that the monochromatic light emitted from laser light source 6 is not limited to HeNe laser light.

[0024] The infrared interference light output from the interferometer 3 is converged on the sample 40 by the mirror 22. The infrared interference light that has passed through the sample 40 is converged on the photodetector 5 by the mirror 23. An interferogram is created based on the intensity signal of the infrared interference light detected by the photodetector 5. In the interferogram, the intensity of the infrared interference light is usually taken as the vertical axis, and the optical path difference between the reflected light from the movable mirror 31 and the reflected light from the fixed mirror 33 is taken as the horizontal axis. In the interferogram, a peak in the intensity of the infrared interference light occurs when the optical path difference is 0. By Fourier transforming the interferogram, a power spectrum is created with the intensity taken as the vertical axis and the wave number (or wavelength) taken as the horizontal axis. The reflectance spectrum or transmittance spectrum of the sample 40 is obtained by dividing the power spectrum obtained when the infrared interference light is irradiated on the sample 40 by the background power spectrum obtained in the absence of the sample 40. Peak information specific to the sample 40 can be obtained from these spectra.

[0025] Next, in order to explain the problem to be solved in the feedback control of the infrared light source 10 in the FTIR 100, a comparative example of the monitor unit 1 will be described with reference to FIG.

[0026] FIG. 3 is a diagram showing a configuration of a monitor unit 9 according to a comparative example. The infrared light source 10 in FIG. 3 corresponds to the infrared light source 10 shown in FIG. 1. As shown in FIG. 3, the monitor unit 9 includes a photodetector 91 and a light amount control unit 92. The infrared light source 10 includes a case 101 and an infrared element 102. An opening 103 is formed on a side surface of the case 101. The infrared element 102 is accommodated in the case 101. When power is supplied to the infrared element 102 from the light amount control unit 92, the infrared element 102 generates heat, and radiant light including infrared light is generated from the infrared element 102. The radiant light is emitted from the opening 103.

[0027] The photodetector 91 includes a photodetector element 911 and a signal processor 910. The photodetector element 911 has a light receiving sensitivity to a specific wavelength range of light emitted from the infrared light source 10. The photodetector element 911 outputs a voltage V according to light included in the wavelength range (sensitivity wavelength range) to the light amount controller 92 via the signal processor 910. The photodetector element 911 may be, for example, an InGaAs type photodiode having a light receiving sensitivity in the near infrared range, a SiPIN type photodiode having a light receiving sensitivity in the visible range (380 nm to 780 nm), or a color sensor. The signal processor 910 performs a predetermined process (for example, AD (Analog-to-Digital) conversion) on the signal from the photodetector element 911 and outputs a signal corresponding to the voltage V.

[0028] The light amount control unit 92 includes a differential amplifier 922 having a gain G and a light source driving unit 123. The differential amplifier 922 detects a voltage difference ΔV between the voltage V and a target voltage V0. d is amplified and the signal ΔG is sent to the light source driver 123. d (=G ΔV d The light source driving unit 123 outputs a voltage difference ΔV dThe light source driving unit 123 supplies power to the infrared light source 10 so that Vref becomes zero. The light source driving unit 123 includes, for example, a DA converter, a differential amplifier, a voltage-current conversion circuit, a current detection resistor, and a feedback circuit. The voltage-current conversion circuit includes a transistor or a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor). A PWM (Pulse Width Modulation) modulation circuit and a bridge circuit may be used instead of the voltage-current conversion circuit. The feedback circuit negatively feeds back the voltage of the current detected by the current detection resistor to the differential amplifier. The differential amplifier 922 is realized, for example, by firmware or an FPGA (Field Programmable Gate Array).

[0029] The temperature coefficient of the photodetector element 911 is Δβ, and the temperature difference between the temperature of the photodetector 91 and a reference temperature (for example, the temperature of the photodetector 91 when the FTIR 100 is started) is ΔT a If a voltage difference corresponding to the difference between the amount of light emitted from the infrared light source 10 and the target amount of light is ΔV, the voltage V is expressed by the following equation (2).

[0030]

number

[0031] The temperature of the photodetector 91 is T a The measured voltage V in a constant temperature environment that is stable at Ta and the temperature of the photodetector 91 is T b (=T a +ΔT a0 ) is the measured value of voltage V in a constant temperature environment where the Tb Using these, the temperature coefficient Δβ is expressed as in the following equation (3).

[0032]

number

[0033] The target voltage V0 is a value that is determined in advance through theoretical analysis and experiments with an actual device as a voltage that corresponds to a target amount of light emitted from the infrared light source 10. The target voltage V0 is determined so that the temperature T of the infrared element 102 is a certain temperature in the range of 1000K to 1500K. The target voltage V0 may be selected by the user from a plurality of values ​​thus determined in advance, or may be changeable by the user. For a voltage V near the target voltage V0, the relationship between the target voltage V0 and the temperature T is expressed as a linear formula such as the following equation (4).

[0034]

number

[0035] In formula (4), each of the coefficient p and the constant term q is an apparatus constant specific to the FTIR 100 that is determined by the positional relationship between the photodetector 91 and the infrared light source 10 in the FTIR 100, etc. The coefficient p and the constant term q are known values ​​that are measured in advance in a constant temperature environment where the temperature around the photodetector 91 and the infrared light source 10 is constant.

[0036] From equation (2), the simple voltage difference ΔV between the voltage V and the target voltage V0 d (=V-V0) is expressed as the following equation (5).

[0037]

number

[0038] From equation (5), the voltage difference ΔV d In addition to the voltage difference ΔV, a value derived from the temperature characteristics of the light detection element 911 is included in the voltage difference ΔV. d is different from the voltage difference ΔV, so the voltage difference ΔV d However, it is difficult to bring the amount of light emitted from the infrared light source 10 close to the target amount of light by feedback control based on the voltage difference ΔV. In order to improve the accuracy of the light amount control of the infrared light source 10, it is necessary to perform feedback control based on the voltage difference ΔV. To calculate the voltage difference ΔV from the formula (2), aHowever, since the actual environment in which the FTIR 100 is operated is not a constant temperature environment, the temperature difference ΔT a It is difficult to obtain the temperature difference ΔT in real time. a When is unknown, the voltage difference ΔV cannot be calculated from equation (2).

[0039] Therefore, in the FTIR 100, a voltage difference ΔV and a temperature difference ΔT are calculated using a plurality of voltages output from a plurality of photodiodes having different wavelength sensitivity ranges. a Two or more simultaneous linear equations with unknowns are set up. The temperature difference ΔT a Since it is possible to eliminate the difference between the amount of light emitted from the infrared light source 10 and the target amount of light, the FTIR 100 enables feedback control based on the voltage difference ΔV corresponding to the difference between the amount of light emitted from the infrared light source 10 and the target amount of light, thereby improving the accuracy of the light amount control of the infrared light source 10.

[0040] 4 is a diagram showing a configuration of the monitor unit 1 according to the embodiment. In FIG. 4, the infrared light source 10 and the light source driving unit 123 are similar to the infrared light source 10 and the light source driving unit 123 shown in FIG.

[0041] 4, the photodetector 11 includes a photodetection element 111 (first photodetection element), a photodetection element 112 (second photodetection element), a photodetection element 113, a photodetection element 114 (third photodetection element), and a signal processing unit 110. The light amount control unit 12 includes a calculation unit 121, an amplification unit 122 having a gain G, and a light source driving unit 123.

[0042] The light detection elements 111 to 114 have light receiving sensitivity to wavelength ranges WB1 (400 nm to 540 nm), WB2 (450 nm to 630 nm), WB3 (575 nm to 660 nm), and WB4 (785 nm to 885 nm), respectively, as shown in Fig. 5. Curve C1 in Fig. 5 is the spectrum of light emitted from the infrared light source 10, which corresponds to curve C11 in Fig. 2.

[0043] 4 and 5, the photodetector element 111 detects a voltage V B The light detection element 112 outputs a voltage V according to the light included in the wavelength range WB2. G The light detection element 113 outputs a voltage V according to the light included in the wavelength range WB3. R The light detection element 114 outputs a voltage V according to the light included in the wavelength range WB4. IR The signal processor 110 performs predetermined processing (for example, AD conversion) on the signals from the light detection elements 111 to 114 to output a voltage V B ,V G ,V R ,V IR to the calculation unit 121. The signal processing unit 110 includes, for example, an AD converter.

[0044] The calculation unit 121 calculates the voltage V B ,V G ,V R ,V IR and outputs the voltage difference ΔV to the amplifier 122. The amplifier 122 amplifies the voltage difference ΔV and outputs a signal ΔG (=G·ΔV) to the light source driver 123. The light source driver 123 supplies power to the infrared light source 10 so that the voltage difference ΔV becomes zero.

[0045] The calculation unit 121 and the amplification unit 122 are realized by, for example, firmware or FPGA. The calculation unit 121 includes, for example, a subtractor constructed by a program language or a hardware description language. The amplification unit 122 includes, for example, an amplifier constructed by a program language or a hardware description language as a configuration for amplifying a digital value. The amplification unit 122 may include a DA (Digital-to-Analog) converter that converts a digital value into an analog value, and an operational amplifier that amplifies the analog value. Note that, when the amplification unit 122 outputs an analog value, the light source driving unit 123 does not need to include a DA converter. The calculation unit 121 and the amplification unit 122 may be realized by a processor such as a CPU (Central Processing Unit) that executes a program stored in a memory. The process of deriving the voltage difference ΔV performed by the calculation unit 121 will be described below.

[0046] Voltage V B ,V G ,V R ,V IR Each of these can be expressed as (6) below, similar to the voltage V shown in equation (2).

[0047]

number

[0048] Incidentally, formula (6) is a combination of the following formulas (7A), (7B), (7C), and (7D).

[0049]

number

[0050] In the following, multiple equations that are the same except for the subscripts, such as equations (7A) to (7D), will be expressed together as equation (6).

[0051] In equation (6), the voltage V B0 ,V G0 ,V R0,V IR0 are the target voltages of the light detection elements 111 to 114 corresponding to the target light amount of the light emitted from the infrared light source 10. B ,ΔV G ,ΔV R ,ΔV IR is the voltage difference of each of the photodetection elements 111 to 114 corresponding to the difference between the amount of light emitted from the infrared light source 10 and the target light amount. B ,Δβ G ,Δβ R ,Δβ IR are the temperature coefficients of the light detection elements 111 to 114. a is the temperature difference ΔT in equation (2) a is the same as:

[0052] Target voltage V B0 ,V G0 ,V R0 ,V IR0 is the band gain χ of each of the photodetecting elements 111 to 114. B ,χ G ,χ R ,χ IR and the target voltage V0, it is expressed as the following equation (8).

[0053]

number

[0054] In addition, the voltage difference ΔV B ,ΔV G ,ΔV R ,ΔV IR Also, band gain χ B ,χ G ,χ R ,χ IR and the voltage difference ΔV, it is expressed as the following equation (9).

[0055]

number

[0056] Target voltage V B0 ,VG0 ,V R0 ,V IR0 The voltage V in each vicinity of B ,V G ,V R ,V IR In this case, the band gain χ B ,χ G ,χ R ,χ IR is constant and pre-calculated.

[0057] Temperature coefficient Δβ B ,Δβ G ,Δβ R ,Δβ IR is expressed as the following equation (10), similar to equation (3).

[0058]

number

[0059] In equation (10), the voltage V B_Ta ,V G_Ta ,V R_Ta ,V IR_Ta is the temperature of the photodetector 11. a Voltage V in a constant temperature environment that is stable B ,V G ,V R ,V IR These are the measured values ​​of the voltage V B_Tb ,V G_Tb ,V R_Tb ,V IR_Tb is the temperature of the photodetector 11. b Voltage V in a constant temperature environment that is stable B ,V G ,V R ,V IR are the respective measured values.

[0060] Target voltage V B0 ,V G0 ,V R0 ,V IR0 The voltage V in each vicinity of B ,V G ,V R ,V IRAt this point, the voltage V B ,V G ,V R ,V IR and the temperature T of the infrared element 102 can be expressed as a linear equation such as the following equation (11), similar to equation (4).

[0061]

number

[0062] In equation (11), the coefficient p B ,p G ,p R ,p IR and the constant term q B ,q G ,q R ,q IR Each of the coefficients p is an apparatus constant specific to the FTIR 100, which is determined by the positional relationship between the photodetector 11 and the infrared light source 10 in the FTIR 100. B ,p G ,p R ,p IR and the constant term q B ,q G ,q R ,q IR is a known value that is measured in advance in a constant temperature environment where the temperature around the photodetector 11 and the infrared light source 10 is constant.

[0063] In equations (7A) to (7D) into which equations (8) and (9) are substituted, the unknowns are the voltage difference ΔV and the temperature difference ΔT. a That is, each of the formulas (7A) to (7D) is a two-dimensional linear equation. The temperature difference ΔT a is eliminated to derive the voltage difference ΔV.

[0064] Here, due to multiple reflection or scattering of the HeNe laser light from the laser light source 6 in the interferometer 3, a part of the HeNe laser light may reach the photodetector 11. The wavelength (632.8 nm) of the HeNe laser light is included in the wavelength range WB3 (575 nm to 660 nm) of the photodetector 113. Therefore, the HeNe laser light reaching the photodetector 11 becomes a disturbance that reduces the accuracy in the calculation of the voltage difference ΔV. Therefore, the calculation unit 121 calculates the voltage difference ΔV without using the formula (7C) related to the photodetector 113. Since the influence of the HeNe laser light as a disturbance is eliminated from the process of deriving the voltage difference ΔV, the accuracy of the light amount control of the infrared light source 10 can be further improved.

[0065] The voltage difference ΔV derived from equation (7A) (first two-dimensional linear equation) and equation (7B) (second two-dimensional linear equation), the voltage difference ΔV derived from equation (7B) and equation (7D) (third two-dimensional linear equation), and the voltage difference ΔV derived from equation (7D) and equation (7A) are expressed as the following equations (12), (13), and (14), respectively.

[0066]

number

[0067] The calculation unit 121 outputs any one of the voltage differences ΔV of the formulas (12) to (14) to the amplification unit 122. In order to improve the accuracy of the voltage difference ΔV, the average voltage difference of the three voltage differences ΔV of the formulas (12) to (14) may be output to the amplification unit 122.

[0068] In the embodiment, the photodetector includes four photodetection elements. The number of photodetection elements included in the photodetector is not limited to four, and may be two or more.

[0069] Fig. 6 is a diagram showing a configuration of a photodetector 11A according to a first modification of the embodiment. The configuration of photodetector 11A is a configuration in which photodetector 11 in Fig. 4 is removed from photodetector 11. Since the rest is similar, description will not be repeated.

[0070] Fig. 7 is a diagram showing the configuration of a photodetector 11B according to the second modification of the embodiment. The configuration of photodetector 11B is a configuration in which photodetector 11 in Fig. 4 is modified by removing photodetection elements 112 and 113. Since the rest is similar, description thereof will not be repeated.

[0071] As described above, according to the spectrophotometers according to the embodiment and the first and second modifications, in a spectrophotometer equipped with an infrared light source, it is possible to improve the accuracy of the light amount control of the infrared light source.

[0072] [Aspects] It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0073] (Item 1) A spectrophotometer according to one aspect includes an infrared light source, an interferometer, a first detector, and a monitor. The infrared light source emits output light including light in an infrared wavelength range. The interferometer generates interference light based on the input output light. The first detector detects light generated based on the interference light output from the interferometer and transmitted through or reflected by the sample. The monitor monitors the output of the infrared light source. The monitor includes a second detector and a light amount control unit. The second detector outputs a signal according to the amount of the output light. The light amount control unit is operable to control the infrared light source based on the signal so that the amount approaches a target light amount. The infrared light source emits light in a first wavelength range and light in a second wavelength range different from the first wavelength range. The second detector includes a first light detection element and a second light detection element. The first light detection element outputs a first voltage according to the light in the first wavelength range to the light amount control unit. The second light detection element outputs a second voltage corresponding to the light in the second wavelength range to the light amount control unit.

[0074] According to the spectrophotometer described in paragraph 1, a first voltage corresponding to light in a first wavelength range and a second voltage corresponding to light in a second wavelength range are output from the second detector to the light amount control unit, thereby improving the accuracy of light amount control of the infrared light source.

[0075] (2) In the spectrophotometer described in 1, the first voltage and the second voltage are expressed as a first linear equation with two unknowns and a second linear equation with two unknowns, respectively, in which a voltage difference corresponding to the difference between the amount of emitted light and a target amount of light, and a temperature difference between the temperature of the second detector and a reference temperature are unknowns. The first linear equation with two unknowns includes a temperature coefficient of the first light detection element and a band gain of the first light detection element. The second linear equation with two unknowns includes a temperature coefficient of the second light detection element and a band gain of the second light detection element. The light amount control unit controls the infrared light source based on the voltage difference derived from the first linear equation with two unknowns and the second linear equation with two unknowns.

[0076] According to the spectrophotometer described in paragraph 2, the temperature difference can be eliminated by using two linear equations with two unknowns, and therefore the voltage difference can be derived. As a result, feedback control based on the voltage difference corresponding to the difference between the amount of light emitted from the infrared light source and the target light amount becomes possible, and the accuracy of the light amount control of the infrared light source can be improved.

[0077] (Item 3) In the spectrophotometer described in item 2, the emitted light includes light in a third wavelength range different from each of the first wavelength range and the second wavelength range. The second detector further includes a third photodetector. The third photodetector outputs a third voltage corresponding to the light in the third wavelength range to the light amount control unit. The third voltage is expressed as a third two-dimensional linear equation having unknowns, respectively, a voltage difference and a temperature difference. The third two-dimensional linear equation includes a temperature coefficient of the third photodetector and a band gain of the third photodetector. The light amount control unit controls the infrared light source so that an average voltage difference of the voltage difference derived from the first two-dimensional linear equation and the second two-dimensional linear equation, the voltage difference derived from the second two-dimensional linear equation and the third two-dimensional linear equation, and the voltage difference derived from the third two-dimensional linear equation and the first two-dimensional linear equation approaches 0.

[0078] According to the spectrophotometer described in paragraph 3, the infrared light source is controlled based on the average voltage difference of a plurality of voltage differences, so that the accuracy of the light amount control of the infrared light source can be further improved.

[0079] (4) In the spectrophotometer according to any one of the above items 1 to 3, the spectrophotometer further includes a monochromatic light source. The monochromatic light source emits monochromatic light for controlling the interferometer. At least one of the first wavelength range and the second wavelength range does not include the wavelength of the monochromatic light.

[0080] According to the spectrophotometer described in paragraph 4, the influence of monochromatic light as a disturbance is eliminated from the process of deriving the voltage difference, so that the accuracy of the light amount control of the infrared light source can be improved.

[0081] With regard to the above-mentioned embodiments and modified examples, it has been intended from the outset of the application that the configurations described in the embodiments may be appropriately combined, including combinations not mentioned in the specification, to the extent that no inconvenience or contradiction arises.

[0082] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0083] 1,9 monitor section, 3 interferometer, 4 sample chamber, 5,11,11A,11B,60,91 photodetector, 6 laser light source, 10 infrared light source, 12,92 light quantity control section, 21 collimating mirror, 22,23,61-63 mirror, 31 movable mirror, 32 beam splitter, 33 fixed mirror, 40 sample, 101 case, 102 infrared element, 110,910 signal processing section, 111-114,911 photodetector, 121 calculation section, 122 amplifier section, 123 light source driving section, 922 differential amplifier section.

Claims

1. an infrared light source that emits light including light in an infrared wavelength range; an interferometer that generates interference light based on the input emitted light; a first detector that detects light generated based on the interference light output from the interferometer and transmitted through or reflected by a sample; a monitor unit for monitoring an output of the infrared light source, The monitor unit includes: a second detector that outputs a signal corresponding to the amount of the emitted light; a light amount control unit operable to control the infrared light source based on the signal so that the amount approaches a target light amount; the infrared light source emits light in a first wavelength range and light in a second wavelength range different from the first wavelength range, The second detector is a first light detection element that outputs a first voltage corresponding to light in the first wavelength range to the light amount control unit; a second light detection element that outputs a second voltage corresponding to the light in the second wavelength range to the light amount control unit, the first wavelength range includes a wavelength at which the light receiving sensitivity of the first light detection element is at a peak, The second wavelength range includes a wavelength at which the light receiving sensitivity of the second light detection element is at a peak.

2. An infrared light source that emits output light including light in an infrared wavelength range; an interferometer that generates interference light based on the input emitted light; a first detector that detects light generated based on the interference light output from the interferometer and transmitted through or reflected by a sample; a monitor unit for monitoring an output of the infrared light source, The monitor unit includes: a second detector that outputs a signal corresponding to the amount of the emitted light; a light amount control unit operable to control the infrared light source based on the signal so that the amount approaches a target light amount; the infrared light source emits light in a first wavelength range and light in a second wavelength range different from the first wavelength range, The second detector is a first light detection element that outputs a first voltage corresponding to light in the first wavelength range to the light amount control unit; a second light detection element that outputs a second voltage corresponding to the light in the second wavelength range to the light amount control unit, the first voltage and the second voltage are respectively expressed as a first linear equation with two unknowns and a second linear equation with two unknowns, the unknowns being a voltage difference corresponding to the difference between the amount and the target light amount, and a temperature difference between the temperature of the second detector and a reference temperature; the first two-dimensional linear equation includes a temperature coefficient of the first photodetector element and a band gain of the first photodetector element, the second two-dimensional linear equation includes a temperature coefficient of the second photodetector element and a band gain of the second photodetector element, The light amount control unit controls the infrared light source based on the voltage difference derived from the first linear equation with two unknowns and the second linear equation with two unknowns.

3. the emitted light includes light in a third wavelength range different from each of the first wavelength range and the second wavelength range, the second detector further includes a third light detection element configured to output a third voltage corresponding to the light in the third wavelength range to the light amount control unit, the third voltage is expressed as a third two-dimensional linear equation having each of the voltage difference and the temperature difference as unknowns; the third two-dimensional linear equation includes a temperature coefficient of the third photodetector element and a band gain of the third photodetector element, 3. The spectrophotometer according to claim 2, wherein the light amount control unit controls the infrared light source so that average voltage differences of the voltage difference derived from the first binarized linear equation and the second binarized linear equation, the voltage difference derived from the second binarized linear equation and the third binarized linear equation, and the voltage difference derived from the third binarized linear equation and the first binarized linear equation approach zero.

4. the spectrophotometer further comprises a monochromatic light source that emits monochromatic light for controlling the interferometer; 4. The spectrophotometer according to claim 1, wherein at least one of the first wavelength range and the second wavelength range does not include a wavelength of the monochromatic light.

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