Fourier Transform Infrared Spectrophotometer

Abstract

The Fourier transform infrared spectrophotometer (1) comprises a main interferometer (6), a control interferometer (7), an infrared detector (19), a control light detector (34), a wavelength plate (27) and a support component (70). The wavelength plate (27) is arranged on the optical path of the control light (21) and is arranged between the fixed mirror (14) or the movable mirror (15) and the beam splitter (13). The support component (70) supports the wavelength plate (27). The outer periphery of the wavelength plate (27) includes a supported area supported by the support component (70) and a released area released from the support component (70).

Description

Technical Field

[0001] The present disclosure relates to Fourier transform infrared spectrophotometers. Background Art

[0002] For example, the Fourier transform infrared spectrophotometer disclosed in Japanese Patent Application Laid-Open No. 2-253103 includes an infrared light source, a beam splitter, a fixed mirror, and a movable mirror constituting a double beam interferometer. Laser light for measuring the orientation of the fixed mirror or the movable mirror is introduced into the double beam interferometer. Summary of the invention

[0003] An object of the present disclosure is to provide a Fourier transform infrared spectrophotometer capable of obtaining a stable power spectrum with less temporal variation.

[0004] The Fourier transform infrared spectrophotometer of the present disclosure is provided with a main interferometer, a control interferometer, an infrared detector, a control light detector, a wavelength plate and a supporting component. The main interferometer includes an infrared light source emitting infrared light, a beam splitter, a fixed mirror and a movable mirror. The control interferometer includes a control light source emitting control light, a beam splitter, a fixed mirror and a movable mirror. The infrared detector detects the infrared interference light generated by the main interferometer and passing through the sample or reflected by the sample. The control light detector detects the control interference light generated by the control interferometer. The wavelength plate is arranged on the optical path of the control light and is arranged between the fixed mirror or the movable mirror and the beam splitter. The supporting component supports the wavelength plate. The periphery of the wavelength plate includes a supported area supported by the supporting component and a released area released from the supporting component.

[0005] The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 It is a schematic diagram of a Fourier transform infrared spectrophotometer according to an embodiment.

[0007] Figure 2 This is a schematic partially enlarged view of the Fourier transform infrared spectrophotometer according to the embodiment.

[0008] Figure 3 The embodiment of the Fourier transform infrared spectrophotometer is Figure 2 A schematic partial enlarged sectional view is shown along sectional line III-III.

[0009] Figure 4 It is a schematic plan view of a first control light detector included in the Fourier transform infrared spectrophotometer according to the embodiment.

[0010] Figure 5It is a schematic partially enlarged view of a Fourier transform infrared spectrophotometer according to a first modified example of the embodiment.

[0011] Figure 6 It is a schematic partially enlarged view of a Fourier transform infrared spectrophotometer according to a second modified example of the embodiment.

[0012] Figure 7 It is a schematic partially enlarged view of a Fourier transform infrared spectrophotometer according to a third modified example of the embodiment.

[0013] Figure 8 : is a graph showing the temporal change of the background power spectrum measured using the Fourier transform infrared spectrophotometer of the embodiment.

[0014] Fig. 9 This is a schematic partial enlarged view of a Fourier transform infrared spectrophotometer of a comparative example.

[0015] Fig.10 The Fourier transform infrared spectrophotometer of the comparative example Fig. 9 A schematic partial enlarged cross-sectional view along the section line XX is shown.

[0016] Fig.11 : is a graph showing the temporal change of the background power spectrum measured using the Fourier transform infrared spectrophotometer of the comparative example. DETAILED DESCRIPTION

[0017] Hereinafter, the embodiments of the present disclosure will be described. In addition, the same reference numerals are given to the same configurations, and the description thereof will not be repeated.

[0018] Reference Figures 1 to 4 , the Fourier transform infrared spectrophotometer 1 of the embodiment is described. The Fourier transform infrared spectrophotometer 1 mainly includes a main interferometer 6, a control interferometer 7, an infrared detector 19, a control light detector 34, a mirror angle adjuster 40, a mirror drive device 41, a controller 50, a spectrum generator 60, a wavelength plate 27 and a support member 70. The Fourier transform infrared spectrophotometer 1 may further include a collimating lens 22 and a polarizing beam splitter 30. The Fourier transform infrared spectrophotometer 1 may further include a fixing member 80. The Fourier transform infrared spectrophotometer 1 may also further include a housing 8.

[0019] The main interferometer 6 generates infrared interference light 11i for measuring the power spectrum of the sample 3. Figure 1 The main interferometer 6 includes an infrared light source 10, a beam splitter 13, a fixed mirror 14 and a movable mirror 15. The main interferometer 6 may further include a collimating mirror 12.

[0020] The infrared light source 10 outputs infrared light 11. The infrared light source 10 is, for example, a ceramic light source. The collimator 12 reflects the infrared light 11 toward the beam splitter 13 and collimates the infrared light 11.

[0021] The beam splitter 13 splits the infrared light 11 into a first infrared light 11j directed toward the fixed mirror 14 and a second infrared light 11k directed toward the movable mirror 15. The beam splitter 13 combines the first infrared light 11j reflected by the fixed mirror 14 and the second infrared light 11k reflected by the movable mirror 15. The main interferometer 6 (beam splitter 13) generates infrared interference light 11i as interference light between the first infrared light 11j and the second infrared light 11k, and outputs the infrared interference light 11i toward the sample 3 and the infrared detector 19.

[0022] The mirror driving device 41 is connected to the movable mirror 15. The mirror driving device 41 moves the movable mirror 15 in a direction approaching the beam splitter 13 and a direction away from the beam splitter 13, so as to reciprocate the movable mirror 15. The mirror driving device 41 includes, for example, a piston 41a to which the movable mirror 15 is fixed and a voice coil motor 41b that drives the piston 41a.

[0023] Sometimes when the movable mirror 15 moves, the orientation of the movable mirror 15 (the normal direction of the movable mirror 15) changes. The change in the orientation of the movable mirror 15 changes the intensity and phase of the infrared interference light 11i, resulting in degradation of the interference pattern detected by the infrared detector 19. Therefore, in order to compensate for the change in the orientation of the movable mirror 15, it is necessary to adjust the orientation of the movable mirror 15 or the fixed mirror 14. The mirror angle adjuster 40 adjusts the orientation of the movable mirror 15 or the fixed mirror 14. In the present embodiment, the mirror angle adjuster 40 is disposed on the fixed mirror 14 and adjusts the orientation of the fixed mirror 14 (the normal direction of the fixed mirror 14). The mirror angle adjuster 40 may also be disposed on the movable mirror 15 and adjusts the orientation of the movable mirror 15 (the normal direction of the movable mirror 15). The mirror angle adjuster 40 is, for example, an actuator including a piezoelectric element. Specifically, the orientation of the mirror can be adjusted by changing the shape of the piezoelectric element.

[0024] The infrared interference light 11i output from the main interferometer 6 (beam splitter 13) is reflected and focused by the condenser 17, and is incident on the sample 3 arranged in the sample chamber 4. The infrared interference light 11i passes through the sample 3. The infrared interference light 11i can also be reflected by the sample 3. The infrared interference light 11i passing through the sample 3 or reflected by the sample 3 is reflected and focused by the condenser 18, and is incident on the infrared detector 19. The infrared detector 19 detects the infrared interference light 11i generated by the main interferometer 6 and passing through the sample 3 or reflected by the sample 3 as an interference pattern. The interference pattern is generated as the movable mirror 15 moves. The infrared detector 19 is, for example, a pyroelectric detector or an MCT detector.

[0025] The control interferometer 7 generates control interference light 21i for measuring the position and speed of the movable mirror 15 and the orientation of the fixed mirror 14 or the movable mirror 15. Figure 1 The control interferometer 7 includes a control light source 20, a beam splitter 13, a fixed mirror 14 and a movable mirror 15.

[0026] The control light source 20 outputs the control light 21. The control light source 20 is, for example, a laser light source such as a helium-neon (He-Ne) laser or a semiconductor laser. The control light 21 is, for example, a laser beam. The collimator lens 22 is disposed on the optical path of the control light 21 and is disposed between the control light source 20 and the beam splitter 13. The collimator lens 22 collimates the control light 21.

[0027] The mirror 26 reflects the control light 21 output from the collimating lens 22 toward the beam splitter 13. The mirror 26 can be arranged in the infrared light 11. In order to reduce the infrared light 11 blocked by the mirror 26, the size of the mirror 26 is smaller than the beam diameter of the infrared light 11. The control light 21 advances in parallel with the infrared light 11 and is incident on the beam splitter 13. The optical axis 21p of the control light 21 is parallel to the optical axis 11p of the infrared light 11. The beam diameter of the control light 21 is smaller than the beam diameter of the infrared light 11.

[0028] The beam splitter 13 splits the control light 21 into a first control light 21j directed toward the fixed mirror 14 and a second control light 21k directed toward the movable mirror 15. The beam splitter 13 combines the first control light 21j reflected by the fixed mirror 14 and the second control light 21k reflected by the movable mirror 15. The control interferometer 7 (beam splitter 13) generates a control interference light 21i as interference light between the first control light 21j and the second control light 21k, and outputs the control interference light 21i toward the infrared detector 19.

[0029] The wavelength plate 27 is arranged on the optical path of the control light 21. The wavelength plate 27 is arranged between the fixed mirror 14 and the beam splitter 13. The wavelength plate 27 can also be arranged between the movable mirror 15 and the beam splitter 13. The wavelength plate 27 is formed of a transparent material such as artificial crystal, for example. The wavelength plate 27 is, for example, a one-eighth wavelength plate (λ / 8 plate). In the case where the wavelength plate 27 is a one-eighth wavelength plate, if the linearly polarized control light 21 passes through the wavelength plate 27 once, the phase of the polarization component of the slow phase axis direction of the wavelength plate 27 in the control light 21 is delayed by 45° relative to the phase of the polarization component of the fast phase axis direction of the wavelength plate 27 in the control light 21. The control light 21 is reflected by the fixed mirror 14 or the movable mirror 15. Since the control light 21 is reflected by the fixed mirror 14 or the movable mirror 15, the control light 21 passes through the wavelength plate 27 twice. The phase of the polarization component in the slow phase axis direction of the wavelength plate 27 in the control light 21 is delayed by 90° relative to the phase of the polarization component in the fast phase axis direction of the wavelength plate 27 in the control light 21. In this way, the control light 21 (first control light 21j) having linear polarization is converted into the control light 21 (first control light 21j) having circular polarization.

[0030] Reference Figure 2 and Figure 3 The supporting member 70 supports the wavelength plate 27. The periphery of the wavelength plate 27 includes a supported area supported by the supporting member 70 and a released area released from the supporting member 70. The released area of ​​the periphery of the wavelength plate 27 is, for example, more than one-third of the periphery length of the wavelength plate 27. The released area of ​​the periphery of the wavelength plate 27 may also be more than one-half of the periphery length of the wavelength plate 27. The supporting member 70 includes, for example, a mounting portion 72 and a column 71. The supporting member 70 (mounting portion 72) supports, for example, one side of the periphery of the wavelength plate 27. The remaining three sides of the periphery of the wavelength plate 27 are released from the supporting member 70 (mounting portion 72). The supporting member 70 (mounting portion 72) supports, for example, the lower portion of the wavelength plate 27.

[0031] The support member 70 is formed of a material different from that of the wave plate 27. The support member 70 is formed of a metal material such as stainless steel or aluminum, for example. The thermal expansion coefficient of the support member 70 is different from that of the wave plate 27. The mounting portion 72 includes a base 73. A slit 78 is provided in the mounting portion 72 (base 73). A hole 79 is provided in the mounting portion 72 (base 73). The wave plate 27 is inserted into the slit 78.

[0032] The column 71 is connected to the mounting portion 72 (base 73). In a top view from the direction of the optical axis 11p of the infrared light 11 (the first infrared light 11j), the column 71 has a width narrower than that of the mounting portion 72. The width of the column 71 is, for example, less than 50% of the width of the mounting portion 72. The width of the column 71 may be less than 40% of the width of the mounting portion 72, less than 30% of the width of the mounting portion 72, or less than 20% of the width of the mounting portion 72. In a top view from the direction of the optical axis 11p of the infrared light 11 (the first infrared light 11j), the column 71 may also have a width narrower than that of the wavelength plate 27. The column 71 is mounted on the housing 8. In the present embodiment, the column 71 is mounted on the bottom wall of the housing 8. The column 71 may be mounted directly on the housing 8, or may be mounted on the housing 8 via other components (not shown).

[0033] The fixing member 80 attaches the wave plate 27 to the supporting member 70 (for example, the mounting portion 72 (base 73 )). The fixing member 80 includes, for example, an elastic spacer 81 , a plate 82 , and a pressing member 84 .

[0034] The elastic spacer 81 is formed of, for example, silicone rubber. The elastic spacer 81 is inserted into the slit 78 and is disposed between the mounting portion 72 (base 73) and the wave plate 27. The wave plate 27 may also be clamped by the elastic spacer 81. The first thermal conductivity of the elastic spacer is, for example, 30% or less of the second thermal conductivity of the wave plate 27. The first thermal conductivity of the elastic spacer may be 20% or less of the second thermal conductivity of the wave plate 27, or may be 10% or less of the second thermal conductivity of the wave plate 27. Therefore, the elastic spacer reduces the heat conduction between the wave plate 27 and the supporting member 70.

[0035] The plate 82 is in contact with the elastic spacer 81. The plate 82 may also be inserted into the slit 78. The pressing member 84 presses the plate 82 toward the elastic spacer 81 and the wavelength plate 27. The pressing member 84 passes through the hole 79. The pressing member 84 is, for example, a bolt. In this way, the wavelength plate 27 is fixed to the support member 70 using the fixing member 80. The pressing member 84 presses the wavelength plate 27 via the plate 82. Therefore, it is possible to prevent a large mechanical stress from being locally applied to the wavelength plate 27. The pressing member 84 presses the wavelength plate 27 via the elastic spacer 81. Therefore, it is possible to prevent a large mechanical stress from being locally applied to the wavelength plate 27.

[0036] The control interference light 21i output from the control interferometer 7 (beam splitter 13) advances in parallel with the infrared interference light 11i and is incident on the mirror 28. The mirror 28 can be arranged in the infrared interference light 11i. In order to reduce the infrared interference light 11i blocked by the mirror 28, the size of the mirror 28 is smaller than the beam diameter of the infrared interference light 11i. The beam diameter of the control interference light 21i is smaller than the beam diameter of the infrared interference light 11i. The control interference light 21i is reflected by the mirror 28 and is incident on the control light detector 34. The control light detector 34 detects the control interference light 21i generated by the control interferometer 7. The control light detector 34 is, for example, a photodiode.

[0037] Specifically, the polarization beam splitter 30 is arranged on the optical path of the control interference light 21i and between the beam splitter 13 and the control light detector 34. The control interference light 21i reflected by the mirror 28 is incident on the polarization beam splitter 30. The polarization beam splitter 30 splits the control interference light 21i into the first control interference light 21s and the second control interference light 21t. The first control interference light 21s is, for example, the s-polarization component of the control interference light 21i, and the second control interference light 21t is the p-polarization component of the control interference light 21i. The control interference light 21i is the interference light between the first control light 21j having circular polarization and the second control light 21k having linear polarization. Therefore, the phase difference between the first control interference light 21s and the second control interference light 21t is 90°.

[0038] The control light detector 34 includes a first control light detector 35 and a second control light detector 36. The first control light detector 35 detects the first control interference light 21s. Figure 4 The first control light detector 35 is, for example, a multi-quadrant photodiode (for example, a four-quadrant photodiode) including a plurality of light detection elements 35a, 35b, 35c, and 35d. The plurality of light detection elements 35a, 35b, 35c, and 35d may also be formed on a single semiconductor substrate. The second control light detector 36 detects the second control interference light 21t. The second control light detector 36 is, for example, a single-element photodiode including a single light detection element.

[0039] The controller 50 is composed of at least one of a processor such as a CPU (Central Processing Unit) or a circuit. The controller 50 includes a mirror angle adjustment unit 51, a signal addition unit 52, a mirror position detection unit 53, and a mirror speed adjustment unit 56. The controller 50 can realize the functions of the mirror angle adjustment unit 51, the signal addition unit 52, the mirror position detection unit 53, and the mirror speed adjustment unit 56 by, for example, executing a program stored in a storage unit (not shown) of the controller 50 through a processor.

[0040] The mirror angle adjustment unit 51 controls the operation of the mirror angle adjuster 40 based on the output of the control light detector 34 to adjust the direction of the mirror (for example, the fixed mirror 14). Specifically, the mirror angle adjustment unit 51 adjusts the direction of the mirror (for example, the fixed mirror 14) in a manner such that the phases of the output signals of the plurality of light detection elements 35a, 35b, 35c, and 35d included in the first control light detector 35 are consistent. In this way, the change in the direction of the movable mirror 15 generated when the movable mirror 15 moves is compensated.

[0041] The mirror position detection unit 53 detects the moving direction and position of the movable mirror 15 based on the output of the control light detector 34. Specifically, the mirror position detection unit 53 includes a waveform shaper 54 and an up / down counter 55. The signal addition unit 52 adds the output signals of the plurality of light detection elements 35a, 35b, 35c, and 35d included in the first control light detector 35 to obtain a first output signal of the first control light detector 35. The mirror position detection unit 53 receives the first output signal of the first control light detector 35 from the signal addition unit 52, and receives the second output signal of the second control light detector 36 from the second control light detector 36. The waveform shaper 54 converts the first output signal of the first control light detector 35 into a first pulse train signal. The waveform shaper 54 converts the second output signal of the second control light detector 36 into a second pulse train signal.

[0042] The up / down counter 55 receives the first pulse train signal and the second pulse train signal from the waveform shaper 54. The up / down counter 55 determines the moving direction of the movable mirror 15 based on the phase relationship between the first phase of the first pulse train signal and the second phase of the second pulse train signal. For example, when the first phase of the first pulse train signal leads the second phase of the second pulse train signal by 90°, the up / down counter 55 determines the direction away from the beam splitter 13 as the moving direction of the movable mirror 15. When the first phase of the first pulse train signal lags the second phase of the second pulse train signal by 90°, the up / down counter 55 determines the direction away from the beam splitter 13 as the moving direction of the movable mirror 15. In addition, the number of pulses of the pulse train signal counted by the up / down counter 55 depends on the position of the movable mirror 15. The mirror position detection unit 53 determines the position of the movable mirror 15 based on the moving direction of the movable mirror 15 obtained by the up / down counter 55 and the number of pulses of the pulse train signal.

[0043] The mirror speed adjustment unit 56 controls the mirror driving device 41 to adjust the moving speed of the movable mirror 15. Specifically, the mirror speed adjustment unit 56 controls the mirror driving device 41 so that the frequency of the first pulse train signal obtained by the mirror position detection unit 53 or the first output signal of the first control light detector 35 obtained by the signal addition unit 52 is constant. In this way, the mirror speed adjustment unit 56 moves the movable mirror 15 at a constant speed.

[0044] The spectrum generator 60 is composed of at least one of a processor such as a CPU (Central Processing Unit) or a circuit. The controller 50 and the spectrum generator 60 may be composed of a single computer. The spectrum generator 60 includes a sample holding unit 61, an analog-to-digital conversion unit 62, and a Fourier transform operation unit 63. The spectrum generator 60 may realize the functions of the sample holding unit 61, the analog-to-digital conversion unit 62, and the Fourier transform operation unit 63 by, for example, executing a program stored in a storage unit (not shown) of the controller 50 through a processor.

[0045] The spectrum generator 60 generates a power spectrum of the sample 3 based on the interference pattern detected by the infrared detector 19. Specifically, the first pulse train signal or the second pulse train signal obtained by the mirror position detection unit 53 is input to the sample holding unit 61. The sample holding unit 61 samples the interference pattern detected by the infrared detector 19 at a timing specified by the first pulse train signal or the second pulse train signal. The analog-to-digital conversion unit 62 performs digital conversion on the sampled interference pattern. The Fourier transform operation unit 63 performs Fourier transform on the digitally converted interference pattern. In this way, the power spectrum of the sample 3 is obtained.

[0046] The housing 8 accommodates the optical system of the Fourier transform infrared spectrophotometer 1 including the main interferometer 6 , the control interferometer 7 , the infrared detector 19 , the control photodetector 34 , and the like.

[0047] [Operation of Fourier transform infrared spectrophotometer 1]

[0048] The operation of the Fourier transform infrared spectrophotometer 1 when measuring the position and speed of the movable mirror 15 and the orientation of the fixed mirror 14 or the movable mirror 15 is described. While the movable mirror 15 moves, the position and speed of the movable mirror 15 and the orientation of the fixed mirror 14 or the movable mirror 15 are monitored in real time.

[0049] The polarization beam splitter 30 splits the control interference light 21i output from the control interferometer 7 into the first control interference light 21s and the second control interference light 21t. The first control light detector 35 detects the first control interference light 21s. The second control light detector 36 detects the second control interference light 21t. The mirror angle adjustment unit 51 adjusts the orientation of the mirror (for example, the movable mirror 15) in such a manner that the phases of the output signals of the plurality of light detection elements 35a, 35b, 35c, and 35d included in the first control light detector 35 are consistent.

[0050] The signal adding section 52 adds the output signals of the plurality of light detecting elements 35a, 35b, 35c, and 35d included in the first control light detector 35 to obtain a first output signal of the first control light detector 35. The mirror position detecting section 53 receives the first output signal of the first control light detector 35 from the signal adding section 52, and receives the second output signal of the second control light detector 36 from the second control light detector 36. The waveform shaper 54 converts the first output signal of the first control light detector 35 into a first pulse train signal. The waveform shaper 54 converts the second output signal of the second control light detector 36 into a second pulse train signal.

[0051] The up / down counter 55 receives the first pulse train signal and the second pulse train signal from the waveform shaper 54. The up / down counter 55 determines the moving direction of the movable mirror 15 based on the phase relationship between the first phase of the first pulse train signal and the second phase of the second pulse train signal. In addition, the mirror position detection unit 53 determines the position of the movable mirror 15 based on the moving direction of the movable mirror 15 obtained by the up / down counter 55 and the number of pulses of the pulse train signal.

[0052] The mirror speed adjustment unit 56 controls the mirror driving device 41 so that the frequency of the first pulse train signal obtained by the mirror position detection unit 53 or the output signal of the first control light detector 35 obtained by the signal addition unit 52 is constant. In this way, the mirror speed adjustment unit 56 moves the movable mirror 15 at a constant speed.

[0053] The operation of the Fourier transform infrared spectrophotometer 1 when measuring the power spectrum of the sample 3 will be described.

[0054] The infrared interference light 11i output from the main interferometer 6 passes through the sample 3 or is reflected by the sample 3. The infrared detector 19 detects the infrared interference light 11i passing through the sample 3 or being reflected by the sample 3 as an interference pattern. The interference pattern is generated as the moving mirror 15 moves. The spectrum generator 60 generates a power spectrum of the sample 3 based on the interference pattern detected by the infrared detector 19.

[0055] Specifically, the first pulse train signal or the second pulse train signal obtained by the mirror position detection unit 53 is input to the sample holding unit 61. The sample holding unit 61 samples the interference pattern detected by the infrared detector 19 at the timing specified by the first pulse train signal or the second pulse train signal. The analog-to-digital conversion unit 62 performs digital conversion on the sampled interference pattern. The Fourier transform operation unit 63 performs Fourier transform on the digitally converted interference pattern. In this way, the power spectrum of the sample 3 is obtained.

[0056] [Modifications]

[0057] Reference Figure 5In the Fourier transform infrared spectrophotometer 1 of the first modified example of the present embodiment, the support member 70 includes the column 71 but does not include the mounting portion 72 (see Figure 2 ). The slit 78 is provided in the column 71. The wave plate 27 is mounted on the column 71 using the fixing member 80. The supporting member 70 (column 71) supports, for example, one side of the outer periphery of the wave plate 27. The remaining three sides of the outer periphery of the wave plate 27 are released from the supporting member 70 (column 71). The supporting member 70 (column 71) supports, for example, the side edge of the wave plate 27. The pressing member 84 presses the side edge of the wave plate 27.

[0058] Reference Figure 6 In the Fourier transform infrared spectrophotometer 1 of the second modified example of the present embodiment, the supporting member 70 is different from the supporting member 70 of the first modified example of the present embodiment (see Figure 5 ) is similarly configured, but is different from the support member 70 of the first variant of the present embodiment in that the column 71 has an L shape. The fixing member 80 further includes a pressing member 85 such as a bolt. The wavelength plate 27 is mounted on the column 71 using the fixing member 80. The support member 70 (column 71) supports, for example, two sides of the outer periphery of the wavelength plate 27. The remaining two sides of the outer periphery of the wavelength plate 27 are released from the support member 70 (column 71). The support member 70 (column 71) supports, for example, the side edge of the wavelength plate 27 and the upper edge of the wavelength plate 27. The pressing member 84 presses the side edge of the wavelength plate 27. The pressing member 85 presses the upper edge of the wavelength plate 27.

[0059] Reference Figure 7 In the Fourier transform infrared spectrophotometer 1 of the third modified example of the present embodiment, the wave plate 27 is suspended from the top wall of the housing 8. Specifically, the column 71 is mounted on the top wall of the housing 8. The wave plate 27 is mounted on the mounting portion 72 (base 73) using the fixing member 80. The supporting member 70 (mounting portion 72) supports, for example, one side of the outer periphery of the wave plate 27. The remaining three sides of the outer periphery of the wave plate 27 are released from the supporting member 70 (mounting portion 72). The supporting member 70 (mounting portion 72) supports, for example, the upper edge of the wave plate 27. The pressing member 84 presses the upper edge of the wave plate 27.

[0060] The second control light detector 36 may also be a multi-quadrant photodiode including a plurality of light detection elements. When the second control light detector 36 is a multi-quadrant photodiode, the signal adding unit 52 adds the output signals of the plurality of light detection elements included in the second control light detector 36 to obtain a second output signal of the second control light detector 36. The mirror position detecting unit 53 receives the second output signal of the second control light detector 36 from the signal adding unit 52. The wavelength plate 27 is not limited to an eighth wavelength plate (λ / 8 plate), and may be a quarter wavelength plate (λ / 4 plate) or a half wavelength plate (λ / 2 plate).

[0061] [Function of this embodiment]

[0062] The infrared spectrophotometer of the present embodiment is compared with the Fourier transform infrared spectrophotometer of the comparative example. Figures 1 to 4 The operation of the Fourier transform infrared spectrophotometer 1 shown in FIG. 1 is described below. The Fourier transform infrared spectrophotometer of the comparative example has the same configuration as the Fourier transform infrared spectrophotometer 1 of the embodiment, but is different in the following points. Fig. 9 and Fig.10 In the comparative example, the mounting portion 72 includes a base 73 and a frame 76 provided on the base 73. An opening 76a is provided in the frame 76. The entire periphery of the wave plate 27 is mounted on the mounting portion 72 (frame 76) using an adhesive 88 such as an ultraviolet curable adhesive. That is, the entire periphery of the wave plate 27 is constrained by the support member 70 (mounting portion 72).

[0063] Figure 8 : is a graph showing the temporal change of the background power spectrum acquired using the Fourier transform infrared spectrophotometer 1 of the embodiment. Fig.11 Graphs showing the time-dependent changes in the background power spectrum obtained using the Fourier transform infrared spectrophotometer 1 of the comparative example. The horizontal axes of these graphs show the time from the start of measurement, and the vertical axes of these graphs show the transmittance of the background. In these graphs, the solid lines show the transmittance relative to 1000 cm -1 The dotted line shows the change in the transmittance of the infrared background at the wave number of 2050 cm -1 The single-dot chain line shows the change in the transmittance of the infrared background at the wave number of 2850cm -1 The double-dashed line shows the change in the transmittance of the infrared background with respect to the wave number of 4020cm -1 The temporal variation of the transmittance of the infrared light background at the wave number.

[0064] Will Figure 8 and Fig.11 By comparison, it can be seen that the temporal variation of the background power spectrum of the Fourier transform infrared spectrophotometer 1 of the embodiment is reduced compared with the Fourier transform infrared spectrophotometer of the comparative example. The background power spectrum means the power spectrum obtained by using the Fourier transform infrared spectrophotometer without placing the sample 3 in the sample chamber 4. As such, the temporal variation of the background power spectrum obtained by the Fourier transform infrared spectrophotometer 1 of the present embodiment is smaller than the temporal variation of the background power spectrum obtained by the Fourier transform infrared spectrophotometer of the comparative example, which can be considered as follows.

[0065] In the present embodiment and the comparative example, the support member 70 is irradiated with the infrared light 11. The wavelength plate 27 is irradiated with the infrared light 11 and the control light 21. The infrared light 11 and the control light 21 act as heat sources for the support member 70 and the wavelength plate 27. In addition, while the infrared light source 10 radiates the infrared light 11, heat is generated in the infrared light source 10. While the control light source 20 radiates the control light 21, heat is generated in the control light source 20. The heat generated in the infrared light source 10 and the control light source 20 is transferred to the support member 70 via the housing 8.

[0066] In the comparative example, the entire periphery of the wave plate 27 is constrained by the support member 70 (frame 76). The thermal expansion coefficient of the support member 70 is different from that of the wave plate 27. The wave plate 27 is softer than the support member 70. Therefore, thermal stress caused by the difference between the thermal expansion coefficient of the support member 70 and the thermal expansion coefficient of the wave plate 27 is easily applied to the wave plate 27. Thermal stress is generated in the region of the wave plate 27 through which the first control light 21j passes.

[0067] In addition, the thermal conductivity of the support member 70 is higher than that of the wavelength plate 27. In addition, the support member 70 is mounted on the housing 8 having a larger volume. Since the heat transferred to the support member 70 is diffused to the housing 8, the temperature of the support member 70 is less likely to rise than that of the wavelength plate 27. In addition, in the comparative example, the entire periphery of the wavelength plate 27 is constrained by the support member 70 (frame 76). Therefore, the difference between the temperature of the peripheral portion of the wavelength plate 27 close to the support member 70 (frame 76) and the temperature of the central portion of the wavelength plate 27 away from the support member 70 (frame 76) increases. Due to the uneven temperature distribution in the wavelength plate 27, thermal stress is generated in the region of the wavelength plate 27 through which the first control light 21j passes.

[0068] These thermal stresses cause the physical thickness and refractive index distribution of the region through which the control light 21 (first control light 21j) in the wavelength plate 27 passes to change. The changes in the physical thickness and refractive index distribution in the wavelength plate 27 cause the wavefront of the control light 21 (first control light 21j) that passes through the wavelength plate 27 to be distorted. The distortion of the wavefront of the control light 21 disturbs the phase of the output signal of the first control light detector 35 (photodetection elements 35a, 35b, 35c, 35d) and the phase of the output signal of the second control light detector 36. Therefore, errors occur in the speed of the movable mirror 15 and the orientation of the fixed mirror 14 or the movable mirror 15 measured based on the output signal from the control light detector 34. As a result, it becomes impossible to accurately set the speed of the movable mirror 15 and the orientation of the fixed mirror 14 or the movable mirror 15, and it becomes impossible to accurately detect the position of the movable mirror 15. It becomes impossible to obtain an interference pattern that has less time-varying and stable. It becomes impossible to obtain a power spectrum that has less time-varying and stable.

[0069] In contrast, in the present embodiment, the release area of ​​the outer periphery of the wave plate 27 is released from the support member 70. Therefore, the heat conduction between the wave plate 27 and the support member 70 is reduced. The thermal stress applied to the area through which the control light 21 (first control light 21j) in the wave plate 27 is transmitted due to the difference between the thermal expansion coefficient of the support member 70 and the thermal expansion coefficient of the wave plate 27 is reduced. In addition, the difference between the temperature of the peripheral portion of the wave plate 27 close to the support member 70 (frame 76) and the temperature of the central portion of the wave plate 27 far from the support member 70 (frame 76) is reduced. The thermal stress generated in the area through which the control light 21 (first control light 21j) in the wave plate 27 is transmitted due to the uneven temperature distribution in the wave plate 27 is also reduced.

[0070] In this way, the physical thickness and refractive index distribution variation of the region through which the control light 21 (first control light 21j) in the wavelength plate 27 passes can be reduced. The distortion of the wavefront of the control light 21 (first control light 21j) that has passed through the wavelength plate 27 can be reduced. The speed of the movable mirror 15 and the orientation of the fixed mirror 14 or the movable mirror 15 can be set more accurately based on the output signal from the control light detector 34, and the position of the movable mirror 15 can be detected more accurately. As a result, an interference pattern that changes less over time and is stable can be obtained. A power spectrum that changes less over time and is stable can be obtained.

[0071] [plan]

[0072] Those skilled in the art may understand that the above exemplary embodiments are specific examples of the following schemes.

[0073] (Item 1) A Fourier transform infrared spectrophotometer of one embodiment includes a main interferometer, a control interferometer, an infrared detector, a control light detector, a wavelength plate and a supporting member. The main interferometer includes an infrared light source that emits infrared light, a beam splitter, a fixed mirror and a movable mirror. The control interferometer includes a control light source that emits control light, a beam splitter, a fixed mirror and a movable mirror. The infrared detector detects infrared interference light generated by the main interferometer and passes through a sample or is reflected by the sample. The control light detector detects control interference light generated by the control interferometer. The wavelength plate is arranged on the optical path of the control light and is arranged between the fixed mirror or the movable mirror and the beam splitter. The supporting member supports the wavelength plate. The periphery of the wavelength plate includes a supported area supported by the supporting member and a released area released from the supporting member.

[0074] Therefore, the heat conduction between the wavelength plate and the supporting member is reduced. The thermal stress applied to the area through which the control light in the wavelength plate passes caused by the difference between the thermal expansion coefficient of the supporting member and the thermal expansion coefficient of the wavelength plate is reduced. In addition, the difference between the temperature of the peripheral portion of the wavelength plate close to the supporting member and the temperature of the central portion of the wavelength plate away from the supporting member is reduced. The thermal stress generated in the area through which the control light in the wavelength plate is passed due to the uneven temperature distribution in the wavelength plate is also reduced. In this way, the variation in the physical thickness and refractive index distribution of the area through which the control light in the wavelength plate passes can be reduced. Based on the output signal from the control light detector, the speed of the movable mirror and the orientation of the fixed mirror or the movable mirror can be set more accurately, and the position of the movable mirror can be detected more accurately. As a result, an interference pattern with less time-varying and stable changes can be obtained. A power spectrum with less time-varying and stable changes can be obtained.

[0075] (Item 2) In the Fourier transform infrared spectrophotometer described in Item 1, a release area on the periphery of the wave plate is at least one third of the periphery length of the wave plate.

[0076] Therefore, the physical thickness and refractive index distribution variation of the region through which the control light passes in the wavelength plate can be reduced, and a stable interference pattern with less temporal variation can be obtained. A stable power spectrum with less temporal variation can be obtained.

[0077] (Item 3) In the Fourier transform infrared spectrophotometer described in Item 2, the supporting member supports only one side of the outer periphery of the wave plate.

[0078] Therefore, the physical thickness and refractive index distribution variation of the region through which the control light passes in the wavelength plate can be reduced, and a stable interference pattern with less temporal variation can be obtained. A stable power spectrum with less temporal variation can be obtained.

[0079] (Item 4) The Fourier transform infrared spectrophotometer according to any one of Items 1 to 3 further comprises a fixing member for mounting the wavelength plate on the supporting member. The supporting member is provided with a slit. The wavelength plate is inserted into the slit. The fixing member includes an elastic spacer. The elastic spacer is inserted into the slit and is arranged between the supporting member and the wavelength plate.

[0080] The elastic spacer can mount the wavelength plate to the supporting member without applying large mechanical stress locally to the wavelength plate. Therefore, the physical thickness and refractive index distribution variation of the region through which the control light in the wavelength plate passes can be reduced. An interference pattern with less time variation and stability can be obtained. A power spectrum with less time variation and stability can be obtained.

[0081] (Item 5) In the Fourier transform infrared spectrophotometer described in Item 4, the first thermal conductivity of the elastic spacer is 30% or less of the second thermal conductivity of the wave plate.

[0082] Therefore, the elastic spacer reduces the heat conduction between the wavelength plate and the supporting member. The physical thickness of the region through which the control light passes in the wavelength plate and the change in the refractive index distribution can be reduced. An interference pattern with less time variation and stability can be obtained. A power spectrum with less time variation and stability can be obtained.

[0083] (Item 6) In the Fourier transform infrared spectrophotometer described in Item 4 or 5, the fixing member further includes a plate in contact with the elastic spacer and a pressing member pressing the plate toward the elastic spacer and the wavelength plate.

[0084] Therefore, the wavelength plate can be pressed more uniformly. It is possible to prevent large mechanical stress from being applied locally to the wavelength plate. Therefore, the variation of the physical thickness and refractive index distribution of the region through which the control light in the wavelength plate passes can be reduced. It is possible to obtain an interference pattern that changes less over time and is stable. It is possible to obtain a power spectrum that changes less over time and is stable.

[0085] (Item 7) The Fourier transform infrared spectrophotometer described in any one of Items 1 to 6 further comprises a housing. The support member includes a mounting portion for mounting the wavelength plate and a column. The column is connected to the mounting portion and is mounted on the housing. In a top view from the direction of the optical axis of the infrared light, the column has a width narrower than the mounting portion.

[0086] Therefore, the infrared light blocked by the supporting member is reduced. The intensity of the infrared interference light is increased. The temperature rise of the column can be suppressed. The speed of the movable mirror and the orientation of the fixed mirror or movable mirror can be set more accurately based on the output signal from the control light detector, and the position of the movable mirror can be detected more accurately. As a result, an interference pattern with less time variation and stability can be obtained. A power spectrum with less time variation and stability can be obtained.

[0087] In addition, the amount of infrared light irradiated to the supporting member is reduced. The temperature rise of the supporting member can be reduced. The change in the physical thickness and refractive index distribution of the region through which the control light in the wavelength plate passes can be reduced. An interference pattern with less time-varying and stable can be obtained. A power spectrum with less time-varying and stable can be obtained.

[0088] (Item 8) The Fourier transform infrared spectrophotometer according to any one of Items 1 to 6 further comprises a housing. The support member includes a column on which the wavelength plate is mounted. The column has a width narrower than that of the wavelength plate and is mounted on the housing.

[0089] Therefore, the infrared light blocked by the supporting member is reduced. The intensity of the infrared interference light is increased. The temperature rise of the column can be suppressed. The speed of the moving mirror and the orientation of the fixed mirror or the moving mirror can be set more accurately based on the output signal from the control light detector, and the position of the moving mirror can be detected more accurately. As a result, an interference pattern with less time variation and stability can be obtained. A power spectrum with less time variation and stability can be obtained.

[0090] In addition, the amount of infrared light irradiated to the supporting member is reduced. The temperature rise of the supporting member can be reduced. The change in the physical thickness and refractive index distribution of the region through which the control light in the wavelength plate passes can be reduced. An interference pattern with less time-varying and stable can be obtained. A power spectrum with less time-varying and stable can be obtained.

[0091] 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 Fourier transform infrared spectrophotometer, It is characterized in that have: a main interferometer, comprising an infrared light source for emitting infrared light, a beam splitter, a fixed mirror, and a movable mirror; A control interferometer, comprising a control light source emitting control light, the beam splitter, the fixed mirror and the movable mirror; an infrared detector for detecting infrared interference light generated by the main interferometer and passing through or reflected by the sample; a control light detector for detecting control interference light generated by the control interferometer; a wavelength plate, arranged on the optical path of the control light and arranged between the fixed mirror or the movable mirror and the beam splitter; a supporting member supporting the wavelength plate, The outer periphery of the wave plate includes a supported region supported by the supporting member and a released region released from the supporting member. The supporting member supports only one side of the outer periphery of the wave plate, The wavelength plate is rectangular, The Fourier transform infrared spectrophotometer further comprises a fixing member for mounting the wavelength plate on the supporting member. The supporting member is provided with a slit, The wavelength plate is inserted into the slit, The fixing member comprises an elastic spacer, The elastic spacer is inserted into the slit and arranged between the supporting member and the wave plate. The first thermal conductivity of the elastic spacer is 30% or less of the second thermal conductivity of the wave plate.

2. The Fourier transform infrared spectrophotometer according to claim 1, It is characterized in that The relief area on the outer periphery of the wave plate is greater than or equal to one third of the outer periphery length of the wave plate.

3. The Fourier transform infrared spectrophotometer according to claim 1, It is characterized in that The fixing member further includes: a plate in contact with the elastic spacer; and a pressing member pressing the plate toward the elastic spacer and the wavelength plate.

4. The Fourier transform infrared spectrophotometer according to claim 1, It is characterized in that further comprising a housing, The supporting member includes a mounting portion and a column for mounting the wavelength plate. The column is connected to the mounting portion and is mounted on the housing. The column has a width narrower than that of the mounting portion in a plan view from the direction of the optical axis of the infrared light.

5. The Fourier transform infrared spectrophotometer according to claim 1, It is characterized in that further comprising a housing, The supporting member includes a column for mounting the wavelength plate, The post has a narrower width than the wavelength plate and is mounted to the housing.

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