Spectrophotometer

Abstract

The spectrophotometer with an infrared light source of the present invention improves the accuracy of light quantity control of the infrared light source. The spectrophotometer includes an infrared light source (10), an interferometer, a first detector, and a monitor unit. The monitor unit (1) monitors the output of the infrared light source. The monitor unit includes a second detector (11) and a light quantity control unit (12). The second detector (11) outputs a signal corresponding to the amount of emitted light. The light quantity control unit can control the infrared light source to operate in a manner that brings the amount of emitted light close to the target light quantity based on the signal. The infrared light source emits light in a first wavelength region and light in a second wavelength region different from the first wavelength region. The second detector includes a first light detection element (111) and a second light detection element (112). The first light detection element outputs a first voltage (V) corresponding to the light in the first wavelength region. B The second photodetector outputs the second voltage (V) corresponding to the light in the second wavelength region to the light control unit. G The output is sent to the light quantity control unit.

Description

Technical Field

[0001] The present invention relates to a spectrophotometer with an infrared light source, and more particularly to the control of the infrared light source. Background Art

[0002] Conventionally, there are known spectrophotometers equipped with infrared light sources. For example, the specification of U.S. Patent No. 7119904 discloses a Fourier transform infrared (FTIR) spectrophotometer equipped with a photodetector that outputs a signal corresponding to the amount of light emitted from an infrared light source. In this spectrophotometer, the infrared light source is feedback-controlled based on the voltage difference between the voltage output from the photodetector and the target voltage so that the amount of light emitted from the infrared light source is constant within the target light amount. Summary of the invention

[0003] In the spectrophotometer disclosed in Patent Document 1, in order to control an interferometer including a movable mirror, a laser is emitted to the interferometer. Through multiple reflections or scattering of the laser in the interferometer, a portion of the laser can reach a photodetector. In addition, the physical properties of the components of the photodetector generally have temperature characteristics. Even if the amount of infrared light emitted from the infrared light source is the same, the laser and the temperature characteristics will become interference, and the voltage output from the photodetector may change. Therefore, the actual light amount difference between the amount of emitted light 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 make the amount of emitted light from the infrared light source close to the target light amount through feedback control based on the voltage difference.

[0004] The present invention has been made to solve the above-mentioned technical problems, and an object of the present invention is to improve the accuracy of light quantity control of an infrared light source in a spectrophotometer including an infrared light source.

[0005] The spectrophotometer of the present invention comprises an infrared light source, an interferometer, a first detector and a monitoring unit. The infrared light source emits outgoing light including light in an infrared wavelength region. The interferometer generates interference light based on the input outgoing light. The first detector detects light generated based on the interference light output from the interferometer and transmitted through a sample or reflected to the sample. The monitoring unit monitors the output of the infrared light source. The monitoring unit comprises a second detector and a light quantity control unit. The second detector outputs a signal corresponding to the amount of outgoing light. The light quantity control unit can operate in a manner that controls the infrared light source based on the signal so that the amount approaches a target light quantity. The infrared light source emits light in a first wavelength region and light in a second wavelength region different from the first wavelength region. The second detector comprises a first light detection element and a second light detection element. The first light detection element outputs a first voltage corresponding to the light in the first wavelength region to the light quantity control unit. The second light detection element outputs a second voltage corresponding to the light in the second wavelength region to the light quantity control unit.

[0006] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a schematic configuration diagram of FTIR as an example of the spectrophotometer according to the embodiment.

[0008] Figure 2 It is the spectrum of radiation emitted from an infrared light source.

[0009] Figure 3 It is a diagram showing the configuration of a photodetector and a light amount control unit according to a comparative example.

[0010] Figure 4 It is a diagram showing the configuration of a photodetector and a light amount control unit according to the embodiment.

[0011] Figure 5 It is shown Figure 4 The light detector is a spectrum of a sensitivity wavelength region of a light detection element included in the light detector.

[0012] Figure 6 It is a diagram showing the configuration of a photodetector according to Modification 1 of the embodiment.

[0013] Figure 7 It is a diagram showing the configuration of a photodetector according to Modification 2 of the embodiment. DETAILED DESCRIPTION

[0014] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. In addition, the same reference numerals are used for the same or corresponding parts in the drawings, and the description thereof will not be repeated in principle. In addition, the Fourier transform infrared spectrophotometer will be referred to as FTIR in the following.

[0015] Figure 1 FIG. 1 is a schematic diagram of the structure of FTIR100 as an example of a spectrophotometer according to the embodiment. Figure 1 In the diagram, the X-axis, Y-axis, and Z-axis are orthogonal to each other.

[0016] like Figure 1 As shown, FTIR100 includes: an infrared light source 10, a monitor unit 1, a collimator 21, mirrors 22, 23, an interferometer 3, a sample chamber 4, a light detector 5 (first detector), a laser light source 6 (monochromatic light source), a light detector 60, and mirrors 61, 62, 63.

[0017] The infrared light source 10 emits light including light in an infrared wavelength region (infrared light). The monitor unit 1 includes a photodetector 11 (second detector) and a light quantity control unit 12. The monitor unit 1 monitors the output of the infrared light source 10.

[0018] The interferometer 3 generates infrared interference light based on the outgoing 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-reflecting mirror) 32, and a fixed mirror 33. The movable mirror 31 has a driving mechanism and can move linearly in the X-axis direction. The fixed mirror 33 is configured to be rotatable around a rotation axis parallel to the Z-axis, and the rotation angle is controlled in a manner to follow the movement of the movable mirror 31.

[0019] A sample 40 is arranged in the sample chamber 4. In the FTIR 100, the 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 that has passed through the sample 40. The FTIR 100 may also be configured so that the photodetector 5 detects light generated based on the infrared interference light reflected by the sample 40.

[0020] In addition, the FTIR 100 includes a control device (not shown) that receives and analyzes the signals from the photodetectors 5 and 60 and performs overall control of the FTIR 100. The light intensity control unit 12 may be formed as a part of the control device.

[0021] The infrared light source 10 is, for example, a carbon silicon light source, which is a thermal light source that utilizes black body 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. When an electric current flows through the infrared element, the infrared element is heated to 1000K to 1500K, and radiated light (outgoing light) containing 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 of wavelength λ generated by the infrared element at temperature T is expressed by the Planck radiation formula shown in the following formula (1). In addition, in formula (1), h is Planck's constant, c is the speed of light, and k is the Boltzmann constant.

[0022] [Number 1]

[0023]

[0024] Figure 2 is the spectrum of the radiation emitted from the infrared light source 10. Figure 2 In FIG. 1 , curve C11 represents the radiation spectrum B(λ, T1) at temperature T1. Curve C12 represents the radiation spectrum B(λ, T2) at temperature T2 (<T1). Curve C13 represents the radiation spectrum B(λ, T3) at temperature T3 (<T2). Figure 2 As shown, the radiation spectra B(λ, T1) to B(λ, T3) each have a peak (maximum value) of intensity in a wavelength region of 2 μm to 3 μm included in the infrared region (0.78 μm to 1000 μm).

[0025] In addition, the infrared light source may be switched according to the wavelength region of the infrared light used for analysis. For example, when the wavelength region is a near-infrared region (0.78 μm to 2 μm), the infrared light source may be switched to a halogen light source, and when the wavelength region is a mid-infrared region (2 μm to 4 μm) and a far-infrared region (4 μm to 1000 μm), the infrared light source may be switched to a ceramic light source.

[0026] Refer again Figure 1 The photodetector 11 receives the radiation light emitted from the infrared light source 10 and outputs a signal corresponding to the amount of the radiation light to the light quantity control unit 12. The light quantity control unit 12 can operate based on the signal to feedback control the infrared light source 10 in such a way that the amount of the radiation light emitted from the infrared light source 10 approaches the target light quantity.

[0027] The infrared light emitted from the infrared light source 10 as a diffused light beam is converted into a parallel light beam (collimated light) by the collimator 21 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 collimator 21 via an aperture.

[0028] 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 in the beam splitter 32, and infrared interference light is output from the interferometer 3. The intensity (amplitude) of the infrared interference light changes according to the movement of the movable mirror 31.

[0029] The laser light source 6 emits a HeNe laser (monochromatic light) for controlling the interferometer 3. The wavelength of the HeNe laser is 632.8 nm. After passing through the reflector 61, the HeNe laser emitted from the laser light source 6 is reflected by the reflectors 62 and 63 and guided to the beam splitter 32. The HeNe laser guided to the beam splitter 32 is split by the beam splitter 32 into a HeNe laser directed toward the movable mirror 31 and a HeNe laser directed toward the fixed mirror 33. Laser interference light is generated by interference of the reflected light from the movable mirror 31 and the reflected light from the fixed mirror 33 in the beam splitter 32. The laser interference light from the beam splitter 32 is guided to the light detector 60 by the reflectors 63, 62, and 61. When the movable mirror 31 moves at a constant speed, the intensity of the laser interference light is detected as a laser interference fringe signal of a sinusoidal wave of a constant frequency. Based on the interference fringe signal, the position and speed of the movable mirror 31 and the angle of the fixed mirror 33 are controlled. In addition, the monochromatic light emitted from the laser light source 6 is not limited to the HeNe laser.

[0030] The infrared interference light output from the interferometer 3 is converged to the sample 40 by the reflector 22. The infrared interference light that has passed through the sample 40 is converged to the photodetector 5 by the reflector 23. An interference pattern is produced based on the intensity signal of the infrared interference light detected by the photodetector 5. In the interference pattern, usually, the intensity of the infrared interference light is set 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 set as the horizontal axis. In the interference pattern, a peak of the intensity of the infrared interference light will be generated when the optical path difference is 0. By Fourier transforming the interference pattern, a power spectrum with intensity as the vertical axis and wave number (or wavelength) as the horizontal axis is generated. By dividing the power spectrum obtained when the sample 40 is irradiated with infrared interference light by the power spectrum of the background obtained in the absence of the sample 40, the reflectance spectrum or transmittance spectrum of the sample 40 can be obtained. Based on these spectra, peak information unique to the sample 40 can be obtained.

[0031] Next, in order to explain the technical problems to be solved in the feedback control of the infrared light source 10 in the FTIR 100, Figure 3 A comparative example of the monitor unit 1 will be described.

[0032] Figure 3 It is a diagram showing the configuration of the monitor unit 9 of a comparative example. Figure 3 The infrared light source 10 and Figure 1The infrared light source 10 shown corresponds to Figure 3 As shown, the monitor unit 9 includes a photodetector 91 and a light quantity control unit 92. The infrared light source 10 includes a housing 101 and an infrared element 102. An opening 103 is formed on the side of the housing 101. The infrared element 102 is accommodated in the housing 101. When power is supplied to the infrared element 102 from the light quantity 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.

[0033] The photodetector 91 includes a photodetection element 911 and a signal processing unit 910. The photodetection element 911 has photosensitivity to a specific wavelength region of the emitted light from the infrared light source 10. The photodetection element 911 outputs a voltage V corresponding to the light included in the wavelength region (sensitive wavelength region) to the light quantity control unit 92 via the signal processing unit 910. As the photodetection element 911, for example, an InGaAs type photodiode having photosensitivity in the near-infrared region, a SiPIN type photodiode having photosensitivity in the visible region (380nm to 780nm), or a color sensor can be cited. The signal processing unit 910 performs predetermined processing (such as AD (Analog-to-Digital) conversion) on the signal from the photodetection element 911 to output a signal corresponding to the voltage V.

[0034] The light quantity control unit 92 includes a differential amplifier 922 having a gain G and a light source driving unit 123. The differential amplifier 922 converts the voltage difference ΔV between the voltage V and the target voltage V0 into d The amplified signal ΔG is output to the light source driving unit 123 d (=G·ΔV d ). The light source driving unit 123 makes the voltage difference ΔV d The infrared light source 10 is supplied with power in a manner that becomes 0. 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 also 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 unit 922 is implemented, for example, by firmware or an FPGA (Field Programmable Gate Array).

[0035] If the temperature coefficient of the photodetector element 911 is Δβ, the temperature difference between the temperature of the photodetector 91 and the reference temperature (for example, the temperature of the photodetector 91 when the FTIR 100 is started) is ΔT a , assuming that the voltage difference corresponding to the difference between the amount of light emitted from the infrared light source 10 and the target light amount is ΔV, the voltage V is expressed as shown in the following formula (2).

[0036] [Number 2]

[0037] V=V0+ΔV+V0·ΔV·Δβ·ΔT a (2)

[0038] Use the temperature of the photodetector 91 to stabilize at T a The measured value of the voltage V under the constant temperature environment is V Ta and the temperature of the photodetector 91 is stabilized at T b (=T a +ΔT a0 ) is the measured value of the voltage V under the constant temperature environment Tb , the temperature coefficient Δβ is expressed as the following formula (3).

[0039] [Number 3]

[0040]

[0041] The target voltage V0 is a value predetermined by theoretical analysis and actual machine experiments as a voltage corresponding to the target light amount of the emitted light from the infrared light source 10. The target voltage V0 is determined to be a temperature in the range of 1000K to 1500K when the temperature T of the infrared element 102 reaches a certain temperature. The target voltage V0 can be selected by the user from a plurality of values ​​predetermined in this way, or can be changed by the user. In the voltage V near the target voltage V0, the relationship between the target voltage V0 and the temperature T is expressed as a linear equation such as the following equation (4).

[0042] [Number 4]

[0043] T=p·V+q (4)

[0044] In formula (4), coefficient p and constant term q are device constants inherent to FTIR100, which are determined by the positional relationship between the photodetector 91 and the infrared light source 10 in FTIR100, etc. Coefficient p and constant term q are known values ​​that are pre-measured in a constant temperature environment in which the ambient temperature of the photodetector 91 and the infrared light source 10 is constant.

[0045] According to equation (2), the simple voltage difference ΔV between voltage V and target voltage V0 is d (=V-V0) is expressed as the following formula (5).

[0046] [Number 5]

[0047] ΔV d =ΔV+V0·ΔV·Δβ·ΔT a (5)

[0048] According to formula (5), when the voltage difference ΔV d In addition to the voltage difference ΔV, the value of the temperature characteristic of the light detection element 911 is also included. d Different from the voltage difference ΔV, the voltage difference ΔV is d Feedback control makes it difficult to make the amount of light emitted from the infrared light source 10 close to the target light amount. In order to improve the accuracy of the light amount control of the infrared light source 10, feedback control based on the voltage difference ΔV is required. In order to calculate the voltage difference ΔV according to formula (2), it is necessary to calculate the temperature difference ΔT a However, since the actual environment in which the FTIR 100 operates is not a constant temperature environment, it is difficult to obtain the temperature difference ΔT of the photodetector 91 in real time. a . At a temperature difference ΔT a If the voltage difference ΔV is unknown, it is impossible to calculate the voltage difference ΔV according to equation (2).

[0049] Therefore, in the FTIR 100, a plurality of voltages outputted from a plurality of photodiodes having different sensitivity wavelength regions are used to combine the voltage difference ΔV and the temperature difference ΔT. a Since the temperature difference ΔT can be eliminated by using two linear equations with two or more unknown variables, a According to FTIR100, since feedback control based on voltage difference ΔV corresponding to the difference between the amount of emitted light from infrared light source 10 and the target light amount can be performed, the accuracy of light amount control of infrared light source 10 can be improved.

[0050] Figure 4 FIG. 1 is a diagram showing the configuration of the monitor unit 1 according to the embodiment. Figure 4 In the embodiment, the infrared light source 10 and the light source driving unit 123 are Figure 3 The infrared light source 10 and the light source driving unit 123 shown are the same.

[0051] like Figure 4 As shown, 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 quantity control unit 12 includes a calculation unit 121, an amplifier 122 having a gain G, and a light source driving unit 123.

[0052] The light detection elements 111 to 114 are Figure 5 The wavelength region WB1 (400 nm to 540 nm), the wavelength region WB2 (450 nm to 630 nm), the wavelength region WB3 (575 nm to 660 nm), and the wavelength region WB4 (785 nm to 885 nm) shown have photosensitivity. Figure 5 The curve C1 is derived from Figure 2 Curve C11 corresponds to the spectrum of the output light of the infrared light source 10.

[0053] Reference Figure 4 and Figure 5 The light detection element 111 generates a voltage V corresponding to the light included in the wavelength region WB1. B The light is output to the calculation unit 121 via the signal processing unit 110. The light detection element 112 generates a voltage V corresponding to the light included in the wavelength region WB2. G The light is output to the calculation unit 121 via the signal processing unit 110. The light detection element 113 generates a voltage V corresponding to the light included in the wavelength region WB3. R The light is output to the calculation unit 121 via the signal processing unit 110. The light detection element 114 generates a voltage V corresponding to the light included in the wavelength region WB4. IR The signals are output to the calculation unit 121 via the signal processing unit 110. The signal processing unit 110 performs predetermined processing (for example, AD conversion) on the signals from the light detection elements 111 to 114 to convert the signals into the voltage V B 、V G 、V R 、V IR The corresponding signal is output to the calculation unit 121. The signal processing unit 110 includes, for example, an AD converter.

[0054] The calculation unit 121 calculates the voltage V B 、V G 、V R 、V IR The voltage difference ΔV is calculated and output 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.

[0055] The operation unit 121 and the amplifier 122 are implemented, for example, by firmware or FPGA. The operation unit 121, for example, includes a subtractor constructed by a programming language or a hardware description language. The amplifier 122, for example, includes an amplifier constructed by a programming language or a hardware description language as a structure for amplifying a digital value. The amplifier 122 may also 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. In addition, when the amplifier 122 outputs an analog value, the light source driving unit 123 does not need to include a DA converter. The operation unit 121 and the amplifier 122 may also be implemented by a processor such as a CPU (Central Processing Unit) that executes a program stored in a memory. The following describes the process of deriving the voltage difference ΔV performed by the operation unit 121.

[0056] Voltage V B 、V G 、V R 、V IR Similar to the voltage V shown in equation (2), they are expressed as shown in the following (6).

[0057] [Number 6]

[0058]

[0059] In addition, formula (6) is a collection of the following formulas (7A), (7B), (7C), and (7D).

[0060] [Number 7]

[0061] V B =V B0 +ΔV B +V B0 ΔV B ·Δβ B ΔT a (7A)

[0062] V G =V G0 +ΔV G +V G0 ΔV G ·Δβ G ΔT a (7B)

[0063] V R =V R0 +ΔV R +V R0 ΔV R ·Δβ R ΔT a(7C)

[0064] V IR =V IR0 +ΔV IR +V IR0 ΔV IR ·Δβ IR ΔT a (7D)

[0065] Hereinafter, as in formulas (7A) to (7D), a plurality of formulas having the same format except for the subscripts are collectively presented as in formula (6).

[0066] In formula (6), the voltage V B0 、V G0 、V R0 、V IR0 The voltage difference ΔV is the target voltage of each 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 It is the voltage difference between each of the light detection 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. Temperature coefficient Δβ B , Δβ G , Δβ R , Δβ IR is the temperature coefficient of each of the light detection elements 111 to 114. Temperature difference ΔT a The temperature difference ΔT from equation (2) a same.

[0067] Target voltage V B0 、V G0 、V R0 、V IRO The band gain χ of each of the photodetection elements 111 to 114 is used. B , χ G , χ R , χ IR And the target voltage V0 is expressed as the following equation (8).

[0068] [Number 8]

[0069]

[0070] In addition, the voltage difference ΔV B , ΔV G , ΔV R , ΔV IR The band gain χ is also used B , χ G , χ R , χIR and the voltage difference ΔV are expressed as the following equation (9).

[0071] [Number 9]

[0072]

[0073] At the target voltage V B0 、V G0 、V R0 、V IR0 The voltage V B 、V G 、V R 、V IR In the frequency band, the gain χ B , χ G , χ R , χ IR is constant and precomputed.

[0074] Temperature coefficient Δβ B , Δβ G , Δβ R , Δβ IR Similar to the formula (3), it can be expressed as the following formula (10).

[0075] [Number 10]

[0076]

[0077] In formula (10), the voltage V B＿Ta 、V G＿Ta 、V R＿Ta 、V IR＿Ta The temperature of the photodetector 11 is stabilized at T a The voltage V under constant temperature environment B 、V G 、V R 、V IR Respective measured values. Voltage V B_Tb 、V G_Tb 、V R_Tb 、V IR_Tb The temperature of the photodetector 11 is stabilized at T b The voltage V under constant temperature environment B 、V G 、V R 、V IR The respective measurements.

[0078] At the target voltage V B0 、V G0 、V R0 、V IR0 The voltage V B 、VG 、V R 、V IR In the voltage V B 、V G 、V R 、V IR The relationship with the temperature T of the infrared element 102 is expressed as a linear equation such as the following equation (11) similarly to equation (4).

[0079] [Number 11]

[0080]

[0081] In formula (11), the coefficient p B 、p G 、p R 、p IR and the constant term q B ,q G ,q R ,q IR are device constants specific to the FTIR 100 and 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 It is a known value measured in advance in a constant temperature environment where the temperature around the photodetector 11 and the infrared light source 10 is constant.

[0082] In equations (7A) to (7D) with equations (8) and (9) substituted, the unknowns are the voltage difference ΔV and the temperature difference ΔT. a That is, equations (7A) to (7D) are two-variable linear equations. Using two two-variable linear equations selected from equations (7A) to (7D), the temperature difference ΔT is eliminated. a , derive the voltage difference ΔV.

[0083] Here, a portion of the HeNe laser light from the laser light source 6 in the interferometer 3 can reach the photodetector 11 through multiple reflections or scattering. The wavelength of the HeNe laser light (632.8 nm) is included in the wavelength region WB3 (575 nm to 660 nm) of the photodetection element 113. Therefore, the HeNe laser light reaching the photodetector 11 becomes interference that reduces the accuracy in the calculation of the voltage difference ΔV. Therefore, the calculation unit 121 does not use the formula (7C) related to the photodetection element 113 to calculate the voltage difference ΔV. Since the influence of the HeNe laser light as interference is excluded from the derivation process of the voltage difference ΔV, the accuracy of the light quantity control of the infrared light source 10 can be further improved.

[0084] The voltage difference ΔV derived from formula (7A) (the first linear equation in two variables) and formula (7B) (the second linear equation in two variables), the voltage difference ΔV derived from formula (7B) and formula (7D) (the third linear equation in two variables), and the voltage difference ΔV derived from formula (7D) and formula (7A) are expressed as follows: (12), (13), (14), respectively.

[0085] [Number 12]

[0086]

[0087]

[0088]

[0089] The calculation unit 121 outputs any voltage difference ΔV of equations (12) to (14) to the amplifier 122. To improve the accuracy of the voltage difference ΔV, the average voltage difference of the three voltage differences ΔV of equations (12) to (14) may be output to the amplifier 122.

[0090] In the embodiment, the case where the photodetector includes four photodetection elements has been described, but the number of photodetection elements included in the photodetector only needs to be two or more, and is not limited to four.

[0091] Figure 6 1 is a diagram showing the structure of a photodetector 11A according to a first modification of the embodiment. Figure 4 The light detector 11 of FIG. 1 is a structure in which the light detection element 113 is removed. Other than that, the structure is the same and will not be described again.

[0092] Figure 7 1 is a diagram showing the structure of a photodetector 11B according to a second modification of the embodiment. Figure 4The light detector 11 of FIG. 1 is a structure in which the light detection elements 112 and 113 are removed. Other than that, the structure is the same and will not be described again.

[0093] As described above, according to the spectrophotometers of the embodiment and Modifications 1 and 2, in the spectrophotometer including an infrared light source, it is possible to improve the accuracy of light quantity control of the infrared light source.

[0094] [plan]

[0095] Those skilled in the art will appreciate that the above-described exemplary embodiments are specific examples of the following aspects.

[0096] (Item 1) A spectrophotometer of one scheme includes an infrared light source, an interferometer, a first detector, and a monitoring unit. The infrared light source emits outgoing light including light in an infrared wavelength region. The interferometer generates interference light based on the outgoing light input. The first detector detects light generated based on the interference light output from the interferometer and transmitted through a sample or reflected onto the sample. The monitoring unit monitors the output of the infrared light source. The monitoring unit includes a second detector and a light quantity control unit. The second detector outputs a signal corresponding to the amount of outgoing light. The light quantity control unit can operate in a manner that controls the infrared light source based on the signal so that the amount approaches a target light quantity. The infrared light source emits light in a first wavelength region and light in a second wavelength region different from the first wavelength region. The second detector includes a first light detection element and a second light detection element. The first light detection element outputs a first voltage corresponding to the light in the first wavelength region to the light quantity control unit. The second light detection element outputs a second voltage corresponding to the light in the second wavelength region to the light quantity control unit.

[0097] According to the spectrophotometer described in item 1, the accuracy of light quantity control of the infrared light source can be improved by outputting the first voltage corresponding to light in the first wavelength region and the second voltage corresponding to light in the second wavelength region from the second detector to the light quantity control unit.

[0098] (Item 2) In the spectrophotometer described in Item 1, the first voltage and the second voltage are respectively expressed as a first linear equation in two variables and a second linear equation in two variables, in which the voltage difference corresponding to the difference between the amount of emitted light and the target light amount, and the temperature difference between the temperature of the second detector and the reference temperature are respectively set as unknowns. The first linear equation in two variables includes the temperature coefficient of the first light detection element and the band gain of the first light detection element. The second linear equation in two variables includes the temperature coefficient of the second light detection element and the band gain of the second light detection element. The light quantity control unit controls the infrared light source based on the voltage difference derived from the first linear equation in two variables and the second linear equation in two variables.

[0099] According to the spectrophotometer described in item 2, since the temperature difference can be eliminated by using two linear equations of two variables, the voltage difference can be derived. As a result, since feedback control based on the voltage difference corresponding to the difference between the amount of emitted light from the infrared light source and the target light amount can be performed, the accuracy of the light amount control of the infrared light source can be improved.

[0100] (Item 3) In the spectrophotometer described in Item 2, the emitted light includes light in a third wavelength region that is different from the first wavelength region and the second wavelength region. The second detector also includes a third light detection element. The third light detection element outputs a third voltage corresponding to the light in the third wavelength region to the light intensity control unit. The third voltage is expressed as a third linear equation in two variables in which the voltage difference and the temperature difference are respectively set as unknowns. The third linear equation in two variables includes the temperature coefficient of the third light detection element and the band gain of the third light detection element. The light intensity control unit controls the infrared light source so that the average voltage difference of the voltage difference derived from the first linear equation in two variables and the second linear equation in two variables, the voltage difference derived from the second linear equation in two variables and the third linear equation in two variables, and the voltage difference derived from the third linear equation in two variables and the first linear equation in two variables is close to 0.

[0101] According to the spectrophotometer described in item 3, since the infrared light source is controlled based on the average voltage difference of a plurality of voltage differences, the accuracy of light amount control of the infrared light source can be further improved.

[0102] (Item 4) In the spectrophotometer described in any one of Items 1 to 3, the spectrophotometer further comprises a monochromatic light source. The monochromatic light source emits monochromatic light for controlling the interferometer. At least one of the first wavelength region and the second wavelength region does not include a wavelength of the monochromatic light.

[0103] According to the spectrophotometer described in item 4, since the influence of the monochromatic light as interference is excluded from the process of deriving the voltage difference, the accuracy of the light amount control of the infrared light source can be improved.

[0104] In addition, regarding the above-mentioned embodiment and modification examples, it has been planned since the time of filing that the configurations described in the embodiment will be appropriately combined within a range that does not cause incompatibility or contradiction, including combinations not described in the specification.

[0105] The embodiments of the present invention have been described above, but the embodiments disclosed this time should be considered to be illustrative in all aspects and not restrictive. The scope of the present invention is indicated by the claims, and it is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A spectrophotometer, characterized in that: have: an infrared light source that emits output light including light in an infrared wavelength region; An interferometer, generating interference light based on the input output light; a first detector for detecting light generated based on interference light output from the interferometer and transmitted through the sample or reflected on the sample; a monitor unit for monitoring the output of the infrared light source, The monitoring unit includes: a second detector that outputs a signal corresponding to the amount of the emitted light; The light quantity control unit is operable to control the infrared light source based on the signal so as to bring the quantity close to a target light quantity. The infrared light source emits light in a first wavelength region and light in a second wavelength region different from the first wavelength region. The second detector comprises: a first light detection element that outputs a first voltage corresponding to the light in the first wavelength region to the light quantity control unit; The second light detection element outputs a second voltage corresponding to the light in the second wavelength region to the light quantity control unit. The first voltage and the second voltage are respectively expressed as a first linear equation and a second linear equation in two variables, in which a voltage difference corresponding to a difference between the amount and the target light amount and a temperature difference between the temperature of the second detector and a reference temperature are respectively set as unknowns. The first linear equation of two variables includes the temperature coefficient of the first light detection element and the band gain of the first light detection element. The second linear equation includes the temperature coefficient of the second light detection element and the 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 and second linear equations.

2. The spectrophotometer according to claim 1, wherein: The emitted light includes light in a third wavelength region that is different from the first wavelength region and the second wavelength region. The second detector further includes a third light detection element that outputs a third voltage corresponding to the light in the third wavelength region to the light quantity control unit. The third voltage is expressed as a third linear equation in two variables with the voltage difference and the temperature difference respectively being unknown variables. The third linear equation includes the temperature coefficient of the third light detection element and the band gain of the third light detection element. The light quantity control unit controls the infrared light source so that the average voltage difference of the voltage difference derived from the first and second linear equations, the voltage difference derived from the second and third linear equations, and the voltage difference derived from the third and first linear equations is close to 0.

3. The spectrophotometer according to claim 1 or 2, wherein: The spectrophotometer further includes a monochromatic light source for emitting monochromatic light for controlling the interferometer. At least one of the first wavelength region and the second wavelength region does not include the wavelength of the monochromatic light.

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