Fourier transform infrared spectrophotometer

Abstract

To provide a Fourier transform infrared spectrophotometer that can acquire a more accurate interferogram.SOLUTION: A Fourier transform infrared spectrophotometer 1 includes a main interferometer 6, a control interferometer 7, an infrared detector 19, a control light detector 34, and a block-type beam splitter 30. The block-type beam splitter 30 is arranged between a beam splitter 13 and the control light detector 34. An optical axis of the control light detector 34 is inclined with respect to an optical axis 21p of a control interference light 21i.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] For example, the Fourier transform infrared spectrophotometer disclosed in Japanese Patent Laid-Open Publication No. 2-253103 (Patent Document 1) includes an infrared light source, a beam splitter, a fixed mirror, and a movable mirror, which constitute a two-beam interferometer. A laser beam is introduced into the two-beam interferometer to measure the orientation of the fixed mirror or the movable mirror. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2-253103 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a Fourier transform infrared spectrophotometer that can acquire a more accurate interferogram. [Means for solving the problem]

[0005] A Fourier transform infrared spectrophotometer according to one embodiment of the present disclosure includes a main interferometer, a control interferometer, an infrared detector, a control photodetector, and a block beam splitter. The main interferometer includes an infrared light source that outputs infrared light, a beam splitter, a fixed mirror, and a movable mirror. The control interferometer includes a control light source that outputs control light, a beam splitter, a fixed mirror, and a movable mirror. The infrared detector detects infrared interference light that is generated by the main interferometer and passes through or is reflected by the sample. The control photodetector detects the control interference light generated by the control interferometer. The block beam splitter is disposed on the optical path of the control interference light and between the beam splitter and the control photodetector. The normal to the incident surface of the control photodetector is tilted with respect to the optical axis of the control interference light.

[0006] A Fourier transform infrared spectrophotometer according to one embodiment of the present disclosure includes a main interferometer, a control interferometer, an infrared detector, a control photodetector, and at least one of a collimating optical system and a phase plate. The main interferometer includes an infrared light source that outputs infrared light, a beam splitter, a fixed mirror, and a movable mirror. The control interferometer includes a control light source that outputs 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 or reflected by the sample. The control photodetector detects the control interference light generated by the control interferometer. At least one of the collimating optical system or the phase plate is disposed on the optical path of the control light. The collimating optical system is disposed between the control light source and the beam splitter. The phase plate is disposed between the movable mirror and the beam splitter or between the fixed mirror and the beam splitter. The optical axis of at least one of the collimating optical system or the phase plate is tilted with respect to the optical axis of the control light. [Effects of the Invention]

[0007] The Fourier transform infrared spectrophotometer of the present disclosure can obtain a more accurate interferogram. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram of a Fourier transform infrared spectrophotometer according to an embodiment. [Figure 2] 1 is a schematic partial enlarged view of a Fourier transform infrared spectrophotometer according to an embodiment. [Figure 3] FIG. 10 is a schematic partial enlarged view of a Fourier transform infrared spectrophotometer according to a modified example of the embodiment. [Figure 4] 1 is a schematic partial enlarged view of a Fourier transform infrared spectrophotometer according to an embodiment. [Figure 5] 3 is a schematic enlarged plan view of a photodetection surface of a first control photodetector included in the Fourier transform infrared spectrophotometer of the embodiment. FIG. [Figure 6] 1 is a schematic partial enlarged view of a Fourier transform infrared spectrophotometer according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described. Note that the same reference numerals are used to designate the same components, and the description thereof will not be repeated.

[0010] A Fourier transform infrared spectrophotometer 1 according to an embodiment will be described with reference to Figures 1 to 6. The Fourier transform infrared spectrophotometer 1 mainly includes a main interferometer 6, a control interferometer 7, an infrared detector 19, a control photodetector 34, a mirror angle adjuster 45, a mirror driver 47, a controller 50, and a spectrum creator 60. The Fourier transform infrared spectrophotometer 1 may further include a block beam splitter 30. The Fourier transform infrared spectrophotometer 1 may further include at least one of a collimating optical system 22 or a phase plate 27. The Fourier transform infrared spectrophotometer 1 may further include apertures 25, 42, and 43.

[0011] The main interferometer 6 generates infrared interference light 11i for measuring the power spectrum of the sample 3. Referring to Fig. 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.

[0012] The infrared light source 10 outputs infrared light 11. The infrared light source 10 is, for example, a ceramic light source. The collimating mirror 12 reflects the infrared light 11 toward the beam splitter 13 and collimates the infrared light 11.

[0013] 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, which is 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.

[0014] The mirror drive device 47 is connected to the movable mirror 15. The mirror drive device 47 moves the movable mirror 15 in a direction toward the beam splitter 13 and a direction away from the beam splitter 13, thereby causing the movable mirror 15 to reciprocate. The mirror drive device 47 may include, for example, a linear guide (not shown) and a voice coil motor (not shown). The linear guide includes a rail (not shown) and a slider (not shown) to which the movable mirror 15 is attached and which slides on the rail. The voice coil motor slides the slider along the rail.

[0015] When the movable mirror 15 moves, the orientation of the movable mirror 15 (the normal direction of the movable mirror 15) may fluctuate. The fluctuation in the orientation of the movable mirror 15 changes the intensity and phase of the infrared interference light 11i, degrading the interferogram detected by the infrared detector 19. Therefore, it is necessary to adjust the orientation of the movable mirror 15 or the fixed mirror 14 to compensate for the fluctuation in the orientation of the movable mirror 15. The mirror angle adjuster 45 adjusts the orientation of the movable mirror 15 or the fixed mirror 14. In this embodiment, the mirror angle adjuster 45 is provided 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 45 may also be provided on the movable mirror 15, and may adjust the orientation of the movable mirror 15 (the normal direction of the movable mirror 15). The mirror angle adjuster 45 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.

[0016] The infrared interference light 11i output from the main interferometer 6 (beam splitter 13) is reflected and collected by the collecting mirror 17 and enters the sample 3 placed in the sample chamber 4. The infrared interference light 11i passes through the sample 3. The infrared interference light 11i may be reflected by the sample 3. The infrared interference light 11i that passes through or is reflected by the sample 3 is reflected and collected by the collecting mirror 18 and enters the infrared detector 19. The infrared detector 19 detects the infrared interference light 11i that is generated by the main interferometer 6 and that passes through or is reflected by the sample 3 as an interferogram. The interferogram is generated as the movable mirror 15 moves. The infrared detector 19 is, for example, an MCT detector.

[0017] The control interferometer 7 generates a control interference light 21i for measuring the position and velocity of the movable mirror 15 and the orientation of the fixed mirror 14 or the movable mirror 15. Referring to FIG. 1 , the control interferometer 7 includes a control light source 20, a beam splitter 13, the fixed mirror 14, and the movable mirror 15.

[0018] The control light source 20 outputs a 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.

[0019] The collimating optical system 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 collimating optical system 22 includes at least one lens (e.g., a first lens 23 and a second lens 24). The collimating optical system 22 collimates the control light 21.

[0020] As shown in FIG. 2 , the optical axis 22p of the collimating optical system 22 is tilted with respect to the optical axis 21p of the control light 21. A portion of the control light 21 output from the control light source 20 is reflected by the surface of at least one lens in the collimating optical system 22, generating stray light. This stray light is reflected by the exit surface of the control light source 20 and directed toward the control photodetector 34. Tilting the optical axis 22p of the collimating optical system 22 with respect to the optical axis 21p of the control light 21 reduces or eliminates overlap between the stray light and the control interference light 21i on the photodetection surface (photodetection surfaces 36s, 39s) of the control photodetector 34. Specifically, tilting the optical axis 22p of the collimating optical system 22 with respect to the optical axis 21p of the control light 21 prevents the stray light from entering the photodetection surface of the control photodetector 34.

[0021] The optical axis 22p of the collimating optical system 22 is inclined at an angle α of, for example, 0.5° or more with respect to the optical axis 21p of the control light 21. The optical axis 22p of the collimating optical system 22 may be inclined at an angle α of 1.0° or more with respect to the optical axis 21p of the control light 21. This more reliably reduces or eliminates overlap between stray light and the control interference light 21i on the light detection surface (light detection surfaces 36s, 39s) of the control light detector 34. Specifically, this more reliably prevents stray light from entering the light detection surface of the control light detector 34. The optical axis 22p of the collimating optical system 22 is inclined at an angle α of, for example, 5.0° or less with respect to the optical axis 21p of the control light 21. The optical axis 22p of the collimating optical system 22 may be inclined at an angle α of 4.0° or less with respect to the optical axis 21p of the control light 21. This allows the collimating optical system 22 to be miniaturized, thereby miniaturizing the Fourier transform infrared spectrophotometer 1.

[0022] The collimating optical system 22 may be a beam expander. That is, the collimating optical system 22 may collimate the control light 21 and expand the beam diameter of the control light 21. This eliminates stray light from the control interferometer 7 to the control light source 20, preventing harmonics from being superimposed on the control interference light 21i. This allows the speed of the movable mirror 15 and the orientation of the fixed mirror 14 or the movable mirror 15 to be set more accurately, and the position of the movable mirror 15 to be detected more accurately. Specifically, the collimating optical system 22 may include a first lens 23 and a second lens 24. The collimating optical system 22 may be a Keplerian beam expander shown in FIGS. 1 and 2, or a Galilean beam expander.

[0023] The collimating optical system 22 may further include an aperture 25. Stray light is generated when a portion of the control light 21 is reflected by the surface of at least one lens of the collimating optical system 22. The aperture 25 reduces or eliminates the stray light from reaching the exit surface of the control light source 20. Therefore, the aperture 25 more reliably reduces or eliminates overlap between the stray light and the control interference light 21i on the light detection surface (light detection surfaces 36s, 39s) of the control photodetector 34. Specifically, the aperture 25 prevents the stray light from entering the light detection surface of the control photodetector 34.

[0024] 1 and 2, the aperture 25 may be disposed between the first lens 23 and the second lens 24. Specifically, the aperture 25 may be disposed at the focal position of the first lens 23 and the second lens 24 on the optical axis 22p of the collimating optical system 22. As shown in Fig. 3, the aperture 25 may be disposed on the optical axis 21p of the control light 21 on the side of the control light source 20 with respect to the collimating optical system 22.

[0025] As shown in FIG. 1 , mirror 26 reflects control light 21 output from collimating optical system 22 toward beam splitter 13. Mirror 26 may be disposed in infrared light 11. To reduce the amount of infrared light 11 blocked by mirror 26, the size of mirror 26 is smaller than the beam diameter of infrared light 11. Control light 21 travels parallel to infrared light 11 and enters beam splitter 13. Optical axis 21p of control light 21 is parallel to optical axis 11p of infrared light 11. The beam diameter of control light 21 is smaller than the beam diameter of infrared light 11.

[0026] Beam splitter 13 splits control light 21 into first control light 21j directed toward fixed mirror 14 and second control light 21k directed toward movable mirror 15. Beam splitter 13 combines first control light 21j reflected by fixed mirror 14 and second control light 21k reflected by movable mirror 15. Control interferometer 7 (beam splitter 13) generates control interference light 21i, which is interference light between first control light 21j and second control light 21k, and outputs control interference light 21i toward infrared detector 19.

[0027] The phase plate 27 is disposed on the optical path of the control light 21. The phase plate 27 is disposed between the fixed mirror 14 and the beam splitter 13. The phase plate 27 may be disposed between the movable mirror 15 and the beam splitter 13. The phase plate 27 includes, for example, a surface 27a facing the beam splitter 13 and a surface 27b opposite to the surface 27a. The surface 27b faces a mirror (for example, the fixed mirror 14). The phase plate 27 is, for example, an eighth-wave plate (λ / 8 plate). The phase plate 27 converts, for example, the control light 21 (first control light 21j) having linear polarization into the control light 21 (first control light 21j) having circular polarization.

[0028] 4, the optical axis 27p of the phase plate 27 is tilted with respect to the optical axis 21p of the control light 21. Part of the control light 21 is reflected by the surface 27a of the phase plate 27, generating stray light. Tilting the optical axis 27p of the phase plate 27 with respect to the optical axis 21p of the control light 21 reduces or eliminates overlap between the stray light and the control interference light 21i on the photodetection surface (photodetection surfaces 36s, 39s) of the control photodetector 34. Specifically, tilting the optical axis 27p of the phase plate 27 with respect to the optical axis 21p of the control light 21 prevents the stray light from entering the photodetection surface of the control photodetector 34.

[0029] A portion of the control light 21 reflected by a mirror (e.g., the fixed mirror 14) is reflected by the surface 27b of the phase plate 27, generating stray light. The stray light is reflected by a mirror (e.g., the fixed mirror 14) and directed toward the control photodetector 34. Tilting the optical axis 27p of the phase plate 27 with respect to the optical axis 21p of the control light 21 reduces or eliminates overlap between the stray light and the control interference light 21i on the photodetection surface (photodetection surfaces 36s, 39s) of the control photodetector 34. Specifically, tilting the optical axis 27p of the phase plate 27 with respect to the optical axis 21p of the control light 21 prevents the stray light from entering the photodetection surface of the control photodetector 34.

[0030] The optical axis 27p of the phase plate 27 is inclined at an angle β of, for example, 0.5° or more with respect to the optical axis 21p of the control light 21. The optical axis 27p of the phase plate 27 may be inclined at an angle β of 1.0° or more with respect to the optical axis 21p of the control light 21. This more reliably reduces or eliminates overlap between stray light and the control interference light 21i on the photodetection surface (photodetection surfaces 36s, 39s) of the control light detector 34. Specifically, this more reliably prevents stray light from entering the photodetection surface of the control light detector 34. The optical axis 27p of the phase plate 27 is inclined at an angle β of, for example, 5.0° or less with respect to the optical axis 21p of the control light 21. The optical axis 27p of the phase plate 27 may be inclined at an angle β of 4.0° or less with respect to the optical axis 21p of the control light 21. This allows the Fourier transform infrared spectrophotometer 1 to be miniaturized.

[0031] The control interference light 21i output from the control interferometer 7 (beam splitter 13) travels parallel to the infrared interference light 11i and is incident on the mirror 28. The mirror 28 may be disposed 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 photodetector 34.

[0032] The control photodetector detects the control interference light 21i generated by the control interferometer 7. Specifically, the control photodetector includes a first control photodetector 35 and a second control photodetector .

[0033] The block beam splitter 30 is disposed on the optical path of the control interference light 21i and is disposed 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 block beam splitter 30. The block beam splitter 30 is, for example, a polarizing beam splitter. The block beam splitter 30 splits the control interference light 21i into a first control interference light 21s and a second control interference light 21t. When the block beam splitter 30 is a polarizing beam splitter, the first control interference light 21s is, for example, the s-polarized component of the control interference light 21i, and the second control interference light 21t is, for example, the p-polarized component of the control interference light 21i.

[0034] The block beam splitter 30 includes transparent blocks 31 and 32 and a light separation film 33, such as a polarization separation film. The light separation film 33 is, for example, a dielectric multilayer film. The light separation film 33 is provided between the transparent blocks 31 and 32. The block beam splitter 30 includes surfaces 30a and 30b. The first control interference light 21s is emitted from the surface 30a toward the first control photodetector 35. The surface 30a is, for example, perpendicular to the optical axis 21p of the control interference light 21i (first control interference light 21s). The second control interference light 21t is emitted from the surface 30b toward the second control photodetector 38. The surface 30b is, for example, perpendicular to the optical axis 21p of the control interference light 21i (second control interference light 21t).

[0035] 5 and 6, the first control photodetector 35 includes a light receiving element 36 and an outer enclosure 37. The first control photodetector 35 detects the first control interference light 21s.

[0036] The light receiving element 36 includes a light detection surface 36s on which the first control interference light 21s is incident. The light detection surface 36s of the light receiving element 36 is the light detection surface of the first control photodetector 35. The light receiving element 36 is, for example, a photodiode. More specifically, the light receiving element 36 includes a plurality of light detection elements 3 6 a,3 6 b,3 6 c,3 6 d) (for example, a four-segment photodiode). 6 a,3 6 b,3 6 c,3 6 d may be formed on a single semiconductor substrate.

[0037] The light receiving element 36 is disposed within an outer enclosure 37. The outer enclosure 37 may be, for example, a sealing member that seals the light receiving element 36, or a case that houses the light receiving element 36. The first control photodetector 35 includes an incident surface 35i on which the first control interference light 21s is incident. The incident surface 35i of the first control photodetector 35 is, for example, the incident surface of the outer enclosure 37. The incident surface 35i of the first control photodetector 35 is, for example, the incident surface of a sealing member or a light incident window of a case.

[0038] The second control light detector 38 detects the second control interference light 21t. .figure 6, the second control photodetector 38 is a photodetector 3 9 and an outer enclosure 40.

[0039] The light receiving element 39 includes a light detection surface 39s on which the second control interference light 21t is incident. The light detection surface 39s of the light receiving element 39 is the light detection surface of the second control light detector 38. 9 More specifically, the light receiving element 39 may be, for example, a single-element photodiode including a single light detecting element.

[0040] The light receiving element 39 is disposed within an outer enclosure 40. The outer enclosure 40 may be, for example, a sealing member that seals the light receiving element 39, or a case that houses the light receiving element 39. The second control light detector 38 includes an incident surface 38i on which the second control interference light 21t is incident. The incident surface 38i of the second control light detector 38 is, for example, the incident surface of the outer enclosure 40. The incident surface 38i of the second control light detector 38 is, for example, the incident surface of a sealing member or a light incident window of a case.

[0041] 6, the normal (e.g., normals 35p, 38p) of the incident surface (e.g., incident surfaces 35i, 38i) of the control photodetector 34 (first control photodetector 35, second control photodetector 38) is tilted with respect to the optical axis 21p of the control interference light 21i. A portion of the control interference light 21i is reflected by the incident surface of the control photodetector 34, generating stray light. The stray light is reflected by a surface (e.g., surfaces 30a, 30b) of the block beam splitter 30 and directed toward the control photodetector 34. Tilting the normal of the incident surface of the control photodetector 34 with respect to the optical axis 21p of the control light 21 reduces or eliminates overlap between the stray light and the control interference light 21i on the photodetection surface (photodetection surfaces 36s, 39s) of the control photodetector 34. Specifically, tilting the normal to the incident surface of the control photodetector 34 with respect to the optical axis 21p of the control light 21 prevents stray light from entering the photodetection surface of the control photodetector 34.

[0042] The normal (e.g., normals 35p, 38p) of the incident surfaces (e.g., incident surfaces 35i, 38i) of the control photodetectors 34 (first control photodetector 35, second control photodetector 38) is inclined at an angle of, for example, 0.5° or more with respect to the optical axis 21p of the control interference light 21i. The normal to the incident surface of the control photodetector 34 may be inclined at an angle of 1.0° or more with respect to the optical axis 21p of the control interference light 21i. This more reliably reduces or eliminates overlap between stray light on the photodetection surfaces (photodetection surfaces 36s, 39s) of the control photodetector 34 and the control interference light 21i. Specifically, it is possible to more reliably prevent stray light from entering the photodetection surface of the control photodetector 34. The normal is inclined at an angle of, for example, 5.0° or less with respect to the optical axis 21p of the control interference light 21i. The normal to the incident surface of the control photodetector 34 may be inclined at an angle of 4.0° or less with respect to the optical axis 21p of the control interference light 21i. Therefore, the laser detection optical system including the control photodetector 34 and the block beam splitter 30 is made compact, and the Fourier transform infrared spectrophotometer 1 is made compact.

[0043] Specifically, the normal 35p of the incident surface 35i of the first control photodetector 35 is tilted with respect to the optical axis 21p of the first control interference light 21s. Part of the first control interference light 21s is reflected by the incident surface 35i of the first control photodetector 35, generating stray light. The stray light is reflected by the surface 30a of the block beam splitter 30 and directed toward the first control photodetector 35. Tilting the normal 35p of the incident surface 35i of the first control photodetector 35 with respect to the optical axis 21p of the first control interference light 21s reduces or eliminates overlap between the stray light and the first control interference light 21s on the photodetection surface (photodetection surface 36s) of the first control photodetector 35. Specifically, tilting the normal 35p of the incident surface 35i of the first control photodetector 35 with respect to the optical axis 21p of the first control interference light 21s prevents the stray light from entering the photodetection surface of the first control photodetector 35.

[0044] The normal 35p of the incident surface 35i of the first control photodetector 35 is inclined at an angle γ of, for example, 0.5° or more with respect to the optical axis 21p of the first control interference light 21s. The normal 35p of the incident surface 35i of the first control photodetector 35 may be inclined at an angle γ of 1.0° or more with respect to the optical axis 21p of the first control interference light 21s. This more reliably reduces or eliminates overlap between stray light on the photodetection surface (photodetection surface 36s) of the first control photodetector 35 and the first control interference light 21s. Specifically, it is possible to more reliably prevent stray light from entering the photodetection surface of the first control photodetector 35. The normal 35p of the incident surface 35i of the first control photodetector 35 is inclined at an angle γ of, for example, 5.0° or less with respect to the optical axis 21p of the first control interference light 21s. A normal 35p of the incident surface 35i of the first control photodetector 35 may be inclined at an angle γ of 4.0° or less with respect to the optical axis 21p of the first control interference light 21s. This allows the laser detection optical system including the control photodetector 34 and the block beam splitter 30 to be miniaturized, and the Fourier transform infrared spectrophotometer 1 to be miniaturized.

[0045] The normal 38p of the incident surface 38i of the second control photodetector 38 is tilted with respect to the optical axis 21p of the second control interference light 21t. Part of the second control interference light 21t is reflected by the incident surface 38i of the second control photodetector 38, generating stray light. The stray light is reflected by the surface 30b of the block beam splitter 30 and directed toward the second control photodetector 38. Tilting the normal 38p of the incident surface 38i of the second control photodetector 38 with respect to the optical axis 21p of the second control interference light 21t reduces or eliminates overlap between the stray light and the second control interference light 21t on the photodetection surface (photodetection surface 39s) of the second control photodetector 38. Specifically, tilting the normal 38p of the incident surface 38i of the second control photodetector 38 with respect to the optical axis 21p of the second control interference light 21t prevents stray light from entering the photodetection surface of the second control photodetector 38.

[0046] The normal 38p of the incident surface 38i of the second control photodetector 38 is inclined, for example, by an angle δ of 0.5° or more with respect to the optical axis 21p of the second control interference light 21t. The normal 38p of the incident surface 38i of the second control photodetector 38 may be inclined, for example, by an angle δ of 1.0° or more with respect to the optical axis 21p of the second control interference light 21t. This more reliably reduces or eliminates overlap between stray light on the photodetection surface (photodetection surface 39s) of the second control photodetector 38 and the second control interference light 21t. Specifically, it is possible to more reliably prevent stray light from entering the photodetection surface of the second control photodetector 38. The normal 38p of the incident surface 38i of the second control photodetector 38 is inclined, for example, by an angle δ of 5.0° or less with respect to the optical axis 21p of the second control interference light 21t. A normal 38p of the incident surface 38i of the second control photodetector 38 may be inclined at an angle δ of 4.0° or less with respect to the optical axis 21p of the second control interference light 21t. This allows the laser detection optical system including the control photodetector 34 and the block beam splitter 30 to be miniaturized, and the Fourier transform infrared spectrophotometer 1 to be miniaturized.

[0047] Apertures 42 and 43 may be disposed between the block beam splitter 30 and the control photodetector 34. Stray light occurs when a portion of the control interference light 21i is reflected by the incident surface (e.g., incident surfaces 35i and 38i) of the control photodetector 34. The apertures 42 and 43 reduce or eliminate the stray light that reaches the surface (e.g., 30a and 30b) of the block beam splitter 30. Therefore, the apertures 42 and 43 more reliably reduce or eliminate overlap between the stray light and the control interference light 21i on the photodetection surface (e.g., photodetection surfaces 36s and 39s) of the control photodetector 34. Specifically, the apertures 42 and 43 more reliably prevent stray light from entering the photodetection surface of the control photodetector 34.

[0048] Specifically, the aperture 42 may be disposed between the block beam splitter 30 and the first control photodetector 35. Stray light occurs when a portion of the first control interference light 21s is reflected by the incident surface 35i of the first control photodetector 35. The aperture 42 reduces or eliminates the stray light that reaches the surface 30a of the block beam splitter 30. Therefore, the aperture 42 more reliably reduces or eliminates overlap between the stray light and the first control interference light 21s on the photodetection surface (photodetection surface 36s) of the first control photodetector 35. Specifically, the aperture 42 more reliably prevents the stray light from entering the photodetection surface of the first control photodetector 35.

[0049] The aperture 43 may be disposed between the block beam splitter 30 and the second control photodetector 38. Stray light is generated when a portion of the second control interference light 21t is reflected by the incident surface 38i of the second control photodetector 38. The aperture 43 reduces or eliminates the stray light that reaches the surface 30b of the block beam splitter 30. Therefore, the aperture 43 more reliably reduces or eliminates overlap between the stray light and the second control interference light 21t on the photodetection surface (photodetection surface 39s) of the second control photodetector 38. Specifically, the aperture 43 more reliably prevents the stray light from entering the photodetection surface of the second control photodetector 38.

[0050] The controller 50 is configured with at least one of a processor such as a CPU (Central Processing Unit) or an electric 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 may 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, having the processor execute a program stored in a storage unit (not shown) of the controller 50.

[0051] The mirror angle adjustment unit 51 controls the operation of the mirror angle adjuster 45 based on the output of the control photodetector 34, and adjusts the orientation of the mirror (for example, the fixed mirror 14). Specifically, the mirror angle adjustment unit 51 adjusts the orientation of the mirror (for example, the fixed mirror 14) based on the output of the control photodetector 34. 6 a,3 6 b,3 6 c,3 6 The orientation of a mirror (e.g., fixed mirror 14) is adjusted so that the phases of the output signals of d and d are matched. This compensates for the fluctuations in the orientation of movable mirror 15 that occur as it moves, and the interferogram detected by infrared detector 19 can be improved.

[0052] The mirror position detector 53 detects the moving direction and position of the movable mirror 15 based on the output of the control photodetector 34. Specifically, the mirror position detector 53 includes a waveform shaper 54 and an up / down counter 55. The signal adder 52 adds the signal of the plurality of photodetecting elements 3 included in the first control photodetector 35 to the signal of the plurality of photodetecting elements 3 6 a,3 6 b,3 6 c,3 6 d are added together to obtain a first output signal of the first control photodetector 35. The mirror position detection unit 53 receives the first output signal of the first control photodetector 35 from the signal addition unit 52, and also receives the second output signal of the second control photodetector 38 from the second control photodetector 38. The waveform shaper 54 converts the first output signal of the first control photodetector 35 into a first pulse train signal. The waveform shaper 54 converts the second output signal of the second control photodetector 38 into a second pulse train signal. signal Convert to.

[0053] 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 movement direction of the movable mirror 15 from 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, if 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 movement direction of the movable mirror 15 as a direction away from the beam splitter 13. If 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 movement direction of the movable mirror 15 as a direction away from the beam splitter 13. 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 detector 53 identifies the position of the movable mirror 15 from the direction of movement of the movable mirror 15 obtained by the up / down counter 55 and the number of pulses in the pulse train signal.

[0054] Mirror speed adjustment unit 56 controls mirror drive device 47 to adjust the movement speed of movable mirror 15. Specifically, mirror speed adjustment unit 56 controls mirror drive device 47 so that the frequency of the first pulse train signal obtained by mirror position detection unit 53 or the first output signal of first control photodetector 35 obtained by signal addition unit 52 becomes constant. In this way, mirror speed adjustment unit 56 moves movable mirror 15 at a constant speed.

[0055] The spectrum creator 60 is configured with at least one of a processor such as a CPU (Central Processing Unit) or an electric circuit. The controller 50 and the spectrum creator 60 may be configured as a single computer. The spectrum creator 60 includes a sample-and-hold unit 61, an analog-to-digital conversion unit 62, and a Fourier transform operation unit 63. The spectrum creator 60 may realize the functions of the sample-and-hold unit 61, the analog-to-digital conversion unit 62, and the Fourier transform operation unit 63 by, for example, having a processor execute a program stored in a memory unit (not shown) of the controller 50.

[0056] The spectrum creator 60 creates a power spectrum of the sample 3 from the interferogram 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 hold unit 61. The sample hold unit 61 samples the interferogram detected by the infrared detector 19 at the timing determined by the first pulse train signal or the second pulse train signal. The analog-to-digital conversion unit 62 digitally converts the sampled interferogram. The Fourier transform calculation unit 63 Fourier transforms the digitally converted interferogram. In this way, the power spectrum of the sample 3 is obtained.

[0057] [Fourier transform infrared spectrophotometer 1 operation] The operation of the Fourier transform infrared spectrophotometer 1 in measuring the position and velocity of the moving mirror 15 and the orientation of the fixed mirror 14 or the moving mirror 15 will now be described. While the moving mirror 15 is moving, the position and velocity of the moving mirror 15 and the orientation of the fixed mirror 14 or the moving mirror 15 are monitored in real time.

[0058] The block beam splitter 30 splits the control interference light 21i output from the control interferometer 7 into a first control interference light 21s and a second control interference light 21t. The first control light detector 35 detects the first control interference light 21s. The second control light detector 38 detects the second control interference light 21t. The mirror angle adjustment unit 51 adjusts the angle of the mirror 51 by adjusting the angle of the mirror 51. 6 a,3 6 b,3 6 c,3 6 The orientation of a mirror (for example, movable mirror 15) is adjusted so that the phases of the output signals of d match.

[0059] The signal addition unit 52 adds the plurality of photodetecting elements 3 included in the first control photodetector 35. 6 a,3 6 b,3 6 c,3 6d are added together to obtain a first output signal of the first control photodetector 35. The mirror position detection unit 53 receives the first output signal of the first control photodetector 35 from the signal addition unit 52, and also receives the second output signal of the second control photodetector 38 from the second control photodetector 38. The waveform shaper 54 converts the first output signal of the first control photodetector 35 into a first pulse train signal. The waveform shaper 54 converts the second output signal of the second control photodetector 38 into a second pulse train signal. signal Convert to.

[0060] Up / down counter 55 receives the first pulse train signal and the second pulse train signal from waveform shaper 54. Up / down counter 55 determines the movement direction of movable mirror 15 from the phase relationship between the first phase of the first pulse train signal and the second phase of the second pulse train signal. Furthermore, mirror position detection unit 53 determines the position of movable mirror 15 from the movement direction of movable mirror 15 obtained by up / down counter 55 and the number of pulses in the pulse train signal.

[0061] The mirror speed adjusting unit 56 controls the mirror driving device 47 so that the frequency of the first pulse train signal obtained by the mirror position detecting unit 53 or the output signal of the first control photodetector 35 obtained by the signal adding unit 52 is constant. In this way, the mirror speed adjusting unit 56 moves the movable mirror 15 at a constant speed.

[0062] The operation of the Fourier transform infrared spectrophotometer 1 when measuring the power spectrum of the sample 3 will now be described.

[0063] The infrared interference light 11i output from the main interferometer 6 passes through or is reflected by the sample 3. The infrared detector 19 detects the infrared interference light 11i that passes through or is reflected by the sample 3 as an interferogram. The interferogram is generated as the movable mirror 15 moves. The spectrum creator 60 creates a power spectrum of the sample 3 from the interferogram detected by the infrared detector 19.

[0064] 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 hold unit 61. The sample hold unit 61 samples the interferogram detected by the infrared detector 19 at the timing determined by the first pulse train signal or the second pulse train signal. The analog-to-digital conversion unit 62 digitally converts the sampled interferogram. The Fourier transform calculation unit 63 Fourier transforms the digitally converted interferogram. In this way, the power spectrum of the sample 3 is obtained.

[0065] [Variations] At least one of the optical axis 22p of the collimating optical system 22, the optical axis 27p of the phase plate 27, and the normal (normals 35p, 38p) of the incident surface (incident surfaces 35i, 38i) of the control photodetector 34 may be tilted with respect to the optical axis 21p of the control light 21 or the control interference light 21i. The second control photodetector 38 may also include a multi-segment photodiode including multiple photodetector elements. When the second control photodetector 38 is a multi-segment photodiode, the signal adder 52 adds output signals of the multiple photodetector elements included in the second control photodetector 38 to obtain a second output signal of the second control photodetector 38. The mirror position detector 53 receives the second output signal of the second control photodetector 38 from the signal adder 52. The phase plate 27 is not limited to an eighth-wave plate (λ / 8 plate), but may also be a quarter-wave plate (λ / 4 plate) or a half-wave plate (λ / 2 plate).

[0066] [Operation of this embodiment] According to this embodiment, even if stray light occurs in at least one of the collimating optical system 22, the phase plate 27, or the control photodetector 34, it is possible to reduce or eliminate overlap between the stray light and the control interference light 21i on the photodetection surface of the control photodetector 34 (e.g., photodetection surfaces 36s, 39s). Specifically, it is possible to prevent the stray light from entering the photodetection surface of the control photodetector 34. Based on the output signal from the control photodetector 34, it is possible to more accurately set the speed of the movable mirror 15 and the orientation of the fixed mirror 14 or the movable mirror 15, and it is also possible to more accurately detect the position of the movable mirror 15. As a result, it is possible to acquire an interferogram with less change over time and a more stable power spectrum with less change over time.

[0067] [Aspect] It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0068] (Item 1) A Fourier transform infrared spectrophotometer according to one aspect includes a main interferometer, a control interferometer, an infrared detector, a control photodetector, and a block beam splitter. The main interferometer includes an infrared light source that outputs infrared light, a beam splitter, a fixed mirror, and a movable mirror. The control interferometer includes a control light source that outputs control light, a beam splitter, a fixed mirror, and a movable mirror. The infrared detector detects infrared interference light that is generated by the main interferometer and passes through or is reflected by the sample. The control photodetector detects the control interference light generated by the control interferometer. The block beam splitter is disposed on the optical path of the control interference light and is disposed between the beam splitter and the control photodetector. The normal to the incident surface of the control photodetector is tilted with respect to the optical axis of the control interference light.

[0069] Stray light is generated when a portion of the control interference light is reflected by the incident surface of the control photodetector. The stray light is reflected by the surface of the block beam splitter and directed toward the control photodetector. Tilting the normal to the incident surface of the control photodetector with respect to the optical axis of the control interference light can reduce or eliminate the overlap between the stray light and the control interference light on the optical detection surface of the control photodetector. Therefore, while the moving mirror is being moved, the speed of the moving mirror and the orientation of the fixed or moving mirror can be set more accurately based on the output signal from the control photodetector, and the position of the moving mirror can be detected more accurately. The Fourier transform infrared spectrophotometer can acquire more accurate interferograms.

[0070] (Item 2) The Fourier transform infrared spectrophotometer described in item 1 further includes at least one of a collimating optical system or a phase plate. At least one of the collimating optical system or the phase plate is disposed on the optical path of the control light. The collimating optical system is disposed between the control light source and the beam splitter. The phase plate is disposed between the movable mirror and the beam splitter or between the fixed mirror and the beam splitter. The optical axis of at least one of the collimating optical system or the phase plate is tilted with respect to the optical axis of the control light.

[0071] When a Fourier transform infrared spectrophotometer is equipped with a collimating optical system, the Fourier transform infrared spectrophotometer exhibits the following effects. Stray light is generated when a portion of the control light is reflected by the surface of at least one lens in the collimating optical system. The stray light is reflected by the output surface of the control light source and directed toward the control photodetector. Tilting the optical axis of the collimating optical system with respect to the optical axis of the control light can reduce or eliminate overlap between the stray light and the control interference light on the light detection surface of the control photodetector. Therefore, while the movable mirror is being moved, 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 photodetector, and the position of the movable mirror can be detected more accurately. The Fourier transform infrared spectrophotometer can acquire more accurate interferograms.

[0072] When a Fourier transform infrared spectrophotometer is equipped with a phase plate, the Fourier transform infrared spectrophotometer exhibits the following effects. Stray light is generated when part of the control light is reflected from the surface of the phase plate. Tilting the optical axis of the phase plate with respect to the optical axis of the control light can reduce or eliminate overlap between the stray light and the control interference light on the light detection surface of the control photodetector. Therefore, while the movable mirror is being moved, 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 photodetector, and the position of the movable mirror can be detected more accurately. The Fourier transform infrared spectrophotometer can acquire more accurate interferograms.

[0073] (Item 3) The Fourier transform infrared spectrophotometer according to item 1 or 2 further comprises an aperture disposed between the block beam splitter and the control photodetector.

[0074] Stray light occurs when a portion of the control interference light is reflected from the incident surface of the control photodetector. The aperture can reduce or eliminate the stray light that reaches the surface of the block beam splitter. Therefore, the aperture can more reliably reduce or eliminate overlap between the stray light and the control interference light on the light detection surface of the control photodetector. Therefore, while the movable mirror is being moved, the speed of the movable mirror and the orientation of the fixed mirror or movable mirror can be more accurately set based on the output signal from the control photodetector, and the position of the movable mirror can be more accurately detected. The Fourier transform infrared spectrophotometer can acquire more accurate interferograms.

[0075] (Item 4) In the Fourier transform infrared spectrophotometer described in any one of items 1 to 3, the normal to the incident surface of the control photodetector is tilted at an angle of 0.5° to 5.0° with respect to the optical axis of the control interference light.

[0076] Stray light is generated when a portion of the control interference light is reflected from the incident surface of the control photodetector. The stray light is reflected from the surface of the block beam splitter and directed toward the control photodetector. The normal to the incident surface of the control photodetector is tilted by 0.5° or more with respect to the optical axis of the control interference light. This more reliably reduces or eliminates overlap between the stray light and the control interference light on the optical detection surface of the control photodetector. The normal to the incident surface of the control photodetector is tilted by 5.0° or less with respect to the optical axis of the control interference light. This allows the Fourier transform infrared spectrophotometer to be made more compact.

[0077] (Item 5) A Fourier transform infrared spectrophotometer according to one embodiment includes a main interferometer, a control interferometer, an infrared detector, a control light detector, and at least one of a collimating optical system and a phase plate. The main interferometer includes an infrared light source that outputs infrared light, a beam splitter, a fixed mirror, and a movable mirror. The control interferometer includes a control light source that outputs 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 passing through or reflected by the sample. The control light detector detects the control interference light generated by the control interferometer. At least one of the collimating optical system or the phase plate is disposed on the optical path of the control light. The collimating optical system is disposed between the control light source and the beam splitter. The phase plate is disposed between the movable mirror and the beam splitter or between the fixed mirror and the beam splitter. The optical axis of at least one of the collimating optical system or the phase plate is tilted with respect to the optical axis of the control light.

[0078] When a Fourier transform infrared spectrophotometer is equipped with a collimating optical system, the Fourier transform infrared spectrophotometer exhibits the following effects. Stray light is generated when a portion of the control light is reflected by the surface of at least one lens in the collimating optical system. The stray light is reflected by the output surface of the control light source and directed toward the control photodetector. Tilting the optical axis of the collimating optical system with respect to the optical axis of the control light can reduce or eliminate overlap between the stray light and the control interference light on the light detection surface of the control photodetector. Therefore, while the movable mirror is being moved, 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 photodetector, and the position of the movable mirror can be detected more accurately. The Fourier transform infrared spectrophotometer can acquire more accurate interferograms.

[0079] When a Fourier transform infrared spectrophotometer is equipped with a phase plate, the Fourier transform infrared spectrophotometer exhibits the following effects. Stray light is generated when part of the control light is reflected from the surface of the phase plate. Tilting the optical axis of the phase plate with respect to the optical axis of the control light can reduce or eliminate overlap between the stray light and the control interference light on the light detection surface of the control photodetector. Therefore, while the movable mirror is being moved, 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 photodetector, and the position of the movable mirror can be detected more accurately. The Fourier transform infrared spectrophotometer can acquire more accurate interferograms.

[0080] (Item 6) In the Fourier transform infrared spectrophotometer described in item 2 or 5, at least one of the collimating optical system and the phase plate includes a collimating optical system. The collimating optical system includes a first lens, a second lens, and an aperture disposed between the first lens and the second lens.

[0081] Stray light occurs when a portion of the control light is reflected by the surface of at least one lens in the collimating optical system. The aperture can reduce or eliminate the stray light reaching the output surface of the control light source. Therefore, the aperture can more reliably reduce or eliminate overlap between the stray light and the control interference light on the light detection surface of the control light detector. Therefore, while the movable mirror is being moved, the speed of the movable mirror and the orientation of the fixed mirror or movable mirror can be more accurately set based on the output signal from the control light detector, and the position of the movable mirror can be more accurately detected. The Fourier transform infrared spectrophotometer can acquire more accurate interferograms.

[0082] (Item 7) In the Fourier transform infrared spectrophotometer described in item 2, 5, or 6, the optical axis of at least one of the collimating optical system or the phase plate is tilted at an angle of 0.5° to 5.0° with respect to the optical axis of the control light.

[0083] Stray light is generated when a portion of the control light is reflected from the surface of at least one optical axis of the collimating optical system or phase plate. At least one optical axis of the collimating optical system or phase plate is tilted by 0.5° or more with respect to the optical axis of the control light. This more reliably reduces or eliminates overlap between the stray light and the control interference light on the light detection surface of the control light detector. At least one optical axis of the collimating optical system or phase plate is tilted by 5.0° or less with respect to the optical axis of the control light. This allows the Fourier transform infrared spectrophotometer to be miniaturized.

[0084] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0085] 1 Fourier transform infrared spectrophotometer, 3 sample, 4 sample chamber, 6 main interferometer, 7 control interferometer, 10 infrared light source, 11 infrared light, 11i infrared interference light, 11j first infrared light, 11k second infrared light, 11p optical axis, 12 collimating mirror, 13 beam splitter, 14 fixed mirror, 15 moving mirror, 17, 18 focusing mirror, 19 infrared detector, 20 control light source, 21 control light, 21i control interference light, 21j first control light, 21k second control light, 21p optical axis, 21s first control interference light, 21t second control interference light, 22 collimating optical system, 22p optical axis, 23 first lens, 24 second lens, 25 aperture, 26, 28 mirror, 27 phase plate, 27a, 27b surface, 27p optical axis, 30 Block-type beam splitter, 30a, 30b surfaces, 31, 32 transparent blocks, 33 light separation film, 34 control photodetector, 35 first control photodetector 、3 5i incident plane, 35p normal, 36 photodetector, 36a, 36b, 36c, 36d photodetector elements,36s photodetection surface, 37 outer enclosure, 38 second control photodetector, 38i incident surface, 38p normal, 39 photodetector, 39s photodetection surface, 40 outer enclosure, 42, 43 aperture, 45 mirror angle adjuster, 47 mirror drive device, 50 controller, 51 mirror angle adjustment unit, 52 signal addition unit, 53 mirror position detection unit, 54 waveform shaper, 55 up / down counter, 56 mirror speed adjustment unit, 60 spectrum creator, 61 sample hold unit, 62 analog-to-digital conversion unit, 63 Fourier transform calculation unit.

Claims

1. a main interferometer including an infrared light source that outputs infrared light, a beam splitter, a fixed mirror, and a moving mirror; a control light source that outputs control light, a control interferometer including the beam splitter, the fixed mirror, and the movable mirror; an infrared detector that detects infrared interference light generated by the main interferometer and transmitted through or reflected by a sample; a control photodetector that detects control interference light generated by the control interferometer; a collimating optical system disposed on an optical path of the control light, the collimating optical system is disposed between the control light source and the beam splitter; a Fourier transform infrared spectrophotometer, wherein the optical axis of the collimating optical system is tilted with respect to the optical axis of the control light;

2. A Fourier transform infrared spectrophotometer as described in claim 1, wherein the collimating optical system includes a first lens, a second lens, and an aperture positioned between the first lens and the second lens.

3. A Fourier transform infrared spectrophotometer as described in claim 1 or claim 2, wherein the optical axis of the collimated optical system is inclined at an angle of 0.5° to 5.0° relative to the optical axis of the control light.

4. The optical system further comprises a block-type beam splitter disposed on an optical path of the control interference light and between the beam splitter and the control photodetector; 4. The Fourier transform infrared spectrophotometer according to claim 1, wherein a normal to an incident surface of the control photodetector is tilted with respect to an optical axis of the control interference light.

5. A Fourier transform infrared spectrophotometer as described in claim 4, further comprising an aperture positioned between the block beam splitter and the control photodetector.

6. A Fourier transform infrared spectrophotometer as described in either claim 4 or claim 5, wherein the normal to the incident surface of the control light detector is inclined by 0.5° or more and 5.0° or less with respect to the optical axis of the control interference light.

7. a phase plate disposed on the optical path of the control light, the phase plate is disposed between the movable mirror and the beam splitter or between the fixed mirror and the beam splitter; 7. The Fourier transform infrared spectrophotometer according to claim 1, wherein the optical axis of the phase plate is tilted with respect to the optical axis of the control light.

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