JPS63241435A - Interferometer - Google Patents

Abstract

PURPOSE:To eliminate the need for a correcting plate, etc., and to obtain an inexpensive, high-performance interferometer by providing a beam splitter and two reverse reflectors. CONSTITUTION:The beam splitter 19 which is a parallel plane plate made of a uniform material is provided and the two reverse reflectors 23 and 24 are provided at a specific distance from both surfaces of this splitter 19. Then one side surface of the splitter 19 splits incident light and the split incident light beams are reflected by the fixed reverse reflector 23 and movable reverse reflector 24, so that light beams split by one-surface sides of those reflectors 23 and 24 interfere on the other-surface sides. Consequently, neither a correcting plate nor a vapor-deposited film is required and the inexpensive, high-accuracy interferometer which has superior environmental resistance and operates stably is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention splits incident light into two by a beam splitter, gives an optical path difference between the two split lights, and causes them to interfere again on the beam splitter. Regarding a two-beam interferometer.

This type of interferometer is used in a wide range of applications, including optical component inspection equipment, range finders, and interferometric spectrometers.

[Prior art]

A two-beam interference spectrometer is shown in FIG. 7 as an apparatus to which this type of interferometer is applied. In FIG. 7, light emitted from a light source 1 is condensed by an aperture 2, turned into parallel rays by a collimating reflector 3, and divided into two rays 6 and 7 by a semi-transparent film 5 formed by vapor deposition on a substrate 4. It can be divided into The substrate 4 is usually a parallel plane plate and is made of a material that is highly transparent to light. Glass, fused silica, etc. are used for visible spectrometers, and single crystal materials such as KBr, CsI, and KR8-5 are used for infrared spectrometers. For far-infrared light, the substrate 4 and correction plate 8 are not necessary, and the semi-permeable membrane 5 is a polymer membrane such as polyethylene terephthalate.

The correction plate 8 is made of a material with the same thickness as the substrate 4, and is arranged so as to sandwich the semi-transparent film 5. As an example, the light beam split into two at one point A is split by the movable plane mirror 9 and the fixed plane mirror lO. It is reflected and causes interference at point B. At this time, if there is no correction plate 8, the light beam 7 will pass through the substrate 4 twice after being split into two.
The light ray 6 does not pass through even once, and the refractive index of the substrate 4 varies depending on the wavelength of the light, so the optical distance between the fixed reflecting mirror 10 and the semi-transparent film 5 varies depending on the wavelength. If you want to cause interference with a constant optical path difference regardless of the wavelength, by inserting a correction plate 8 of the same thickness and material into the light beam 6, the same wavelength-dependent optical distance as on the light beam 7 side can be set on the light beam 6 side. It is also necessary to make

In the two-beam interference spectrometer shown in FIG. 7, it is necessary that all the lights of wavelengths in the spectral region interfere with each other with the same optical path difference, so the correction plate 8 is always inserted.

The propulsion device 11 is for moving the movable plane mirror 9, and its moving distance, that is, the optical path difference between the light beams 6 and 7, is detected in units of laser wavelength by a laser interferometer 12, and is input into the computer 13 in real time. Ru. The movable plane mirror 9 and the fixed plane mirror 10 are generally equipped with air (not shown) in the bearings in the propulsion device 11, since errors in the light beam reflection direction and optical path difference errors caused by slight inclinations of the mirrors have a significant adverse effect on measurement. bearings are used.

Further, an elevation adjustment device is attached to the fixed plane mirror 10 to periodically adjust the elevation angle of the fixed plane [10].

The light that has interfered with a predetermined optical path difference is irradiated onto the sample 15 by the irradiation mirror 14, and light of various wavelengths is absorbed according to the spectral characteristics of the sample 15, and collected by the condenser mirror 16. Further, the light is focused on a detector 18 by a detector 17, and is inputted to the computer 13 as an electrical output. The computer 13 stores the detector output as data as a function of the optical path difference measured by the radar interferometer described above, and after accumulating predetermined optical path difference data, determines the spectral characteristics by Fourier transformation.

[Problem that the invention seeks to solve]

Substrate configuring the beam splitter 4. Semi-permeable membrane 5 correction plate 8
Among them, board 4. The structure of the semipermeable membrane 5 is shown in FIG. Usually, the substrate 4 is a circular plate, and the thickness of the substrate 4 is required to be about 10% of the outer diameter due to polishing described later. This board 4. The correction plate 8 is made of a light-transmissive material, and for example, in the mid-infrared region, a KBr single-crystal material is generally used. Furthermore, it is necessary to optically polish the surface, but since the KBr crystal is relatively soft and deliquescent as an object to be polished, the cost for polishing is quite high. In addition, the substrate 4 and the correction plate 8 must have the same thickness, which is ±10 μm for a high-resolution spectrometer.
Because a certain degree of accuracy is required.

In addition to the polishing work, there is also the work of making two sheets into a set and making the C thickness uniform, further increasing the cost. In the visible range, the material used is fused silica, so the material cost is relatively low, but the flatness required by polishing is due to the short measurement wavelength.

The flatness must be higher than that for infrared. It is also necessary that the difference in thickness between the substrate 4 and the correction plate 8 be small, which requires approximately the same cost. As described above, the beam splitter 19 contributes a large amount to the cost, amounting to 20 to 40 inches of direct material cost of the spectrometer excluding the computer 13.

Interferometry spectrometers have dramatically improved sensitivity compared to grating-type spectrometers, so their popularity has been remarkable in recent years, and they are becoming indispensable equipment for high-tech business. However, in terms of one-piece case, it is still higher than that of the crating type. In the spectrometer main body, the above-mentioned beam splitter 19 and the computer 13 required for Fourier transform are the main causes of the high price. With the advancement of electronics technology, computers 13 are being developed with low cost and high performance.However, the beam splitter 19 is basically the same as the computer 13 of several tens of years ago, and the appearance of a low cost and high performance beam splitter 19 is expected. It is expected.

The purpose of this invention is to provide an inexpensive and high-performance interferometer using a new beam splitter.

[Means for solving problems]

According to this invention, this is achieved by constructing an interferometer from a beam splitter, which is a parallel plane plate made of a uniform material, and two retroreflectors, each of which is placed a predetermined distance from both sides of the splitter. be done.

[Effect]

With this configuration, the incident light is split by one surface of the beam splitter, each of the split incident lights is reflected by the retroreflector, and the incident light is split by the split surface and another surface. Since the above-mentioned incident light is interfered with, the correction plate that was conventionally required is removed from the interferometer, and since no vapor deposition film is formed, conventional vapor deposition work is not required, and an inexpensive and high-performance interferometer can be provided. . Furthermore, since there is no need to use a material like KBr which has deliquescent properties, is difficult to polish, and is difficult to deposit, it is possible to provide an interferometer with excellent environmental resistance and stable operation.

〔Example〕

First, before showing embodiments of the present invention, the configuration of a retroreflector will be described. A corner cube reflector 20 is shown in FIG. 10(a) as a retroreflector. FIG. 10(a) shows the appearance of the corner cube reflector 2o. 3 perpendicular to each other
It is made up of two plane mirrors.

The incident light ray 21 is reflected three times by three surfaces and is reflected as a reflected light ray 22, but the direction of the reflected light ray 22 is completely opposite to that of the incident light ray 21 and is parallel to it. FIG. 10(b) shows the reflection properties of a two-dimensional corner cube reflector, where an incident light ray 21 emitted from point A is reflected at points B and D and becomes reflected light 22, reaching point E. If the corner cube reflector 2o is tilted around the apex P as shown by the two-dot chain line in FIG. and the direction remains the same,
Also, ABDE=AB'D'E=2xOP. In the two-dimensional case, it is clear from FIG. 14, but the same thing can be proved geometrically in three-dimensional, as shown in FIG. 10(C).

This figure is viewed from a direction making equal angles to each reflective surface of the corner cube reflector 20, and incident light 21 is incident perpendicularly to the plane of the paper and is reflected as a thick solid line to become reflected light 21. At this point, point A and point E, or point B and point B, appear to be in symmetrical positions with respect to vertex P. This is because it is viewed from the same direction as the light ray 21 (equal to the direction in which the light ray 22 is reflected). At this time, even if the reflector is tilted around the apex P,
The length of BCDE is kept constant and its length is equal to 2XOP.

FIG. 2 shows an interferometer according to an embodiment of the present invention.

A fixed corner cube reflector 23 and a movable corner cube reflector 24 are parallel plane plates 2 made of germanium (Ge).
5 are arranged as shown in the figure. A portion of the incident light beam 21 to the interferometer is reflected by points ~ on the falling surface 26 of the plane-parallel plate 25, and the transmitted light is further reflected by the plane-parallel plate 25.
A part of the light is reflected at a point B0 on the back surface 27 of the light, and a part of the light is transmitted. It passes through the apex P of the fixed corner cube reflector 23 to a point 〇 The point where the axis parallel to the reflected light 28 collides with the front surface 26 is 01, passes through the apex P2 of the movable corner cube reflector 24 and reaches a point Bo. The point where the axis parallel to the transmitted light 29 collides with the back surface 27 is defined as Ol. 0.0° is vertical to the front surface 26 (therefore, the back surface 27 is also perpendicular)
, the fixed corner cube reflector 23 is connected to the movable corner cube reflector 24, and the fixed corner cube reflector /a23
Adjust using the x-y stage attached to the Further, the moving direction of the movable corner cube reflection mirror 4 is adjusted by an unillustrated tilting device so that it becomes parallel to the transmitted light 29 at the point Bo.

When the corner cube reflecting mirrors 23 and 24 and the parallel plane plate 25 are arranged in this manner, the light ray 30 reflected by the fixed corner cube reflecting mirror 23 reaches the back surface 27. coincides with the point where the light ray 31 reflected by the movable corner cube reflector 24 reaches the back surface.

We will prove this below.

In other words, according to the laws of reflection and refraction, the reflected ray is 28 degrees and the refracted ray AoB. The three straight lines perpendicular to the front surface 26 and 32 passing through 〇 to one point are on the same plane (this plane is defined as 81), and on the other hand, the ray 30 and the refracted ray C0D. The three straight lines perpendicular to the front surface 26 passing through one point co also lie on the same plane. Since the rays 28 and 30 are parallel and the perpendicular 33 is also parallel, Sl and S are 2+ planes parallel to each other. Therefore, the intersection of the perpendicular 32 and the back surface 27 is A'. , the intersection of the perpendicular line 33 and the back surface 27 is C'. Then, A', Bo is S,
The intersection line between and the back surface 27 is C'oDo, and the intersection line between and the back surface 27 is A', B.

is C'. It is parallel to Do, and since both refraction angles are the same, the lengths are also equal. On the other hand, A due to the properties of the fixed corner cube reflector 23. and C0 are symmetrical with respect to point O, and 0,0 . is the front surface 26 (therefore the back surface 27
) Since A'o and C'o are adjusted vertically, A'o and C'o are point 0'
, and therefore point B.

and point D0 is point 0. It is symmetrical with respect to. Since the point at which the reflected light 31 reaches the back surface is symmetrical to the point Bo with respect to one point 0□, it ends up coinciding with Do, and the light rays 31 and 30 interfere with each other.

The rays reflected without passing through point B are A+, Bs
.

A2. B2... is also split into transmitted light and reflected light, and these lights interfere at points C, D, C2D2... The light rays that interfered with ClC2... on the front surface 26 are returned to the light incident side, while the light rays that interfered with DoDID2... on the back surface 27 are emitted as output from the interferometer. DoD when the incident light t is 1! Let E, E, B2... be the amplitude intensity of the emitted light that interfered with D2.... For example, in B2) ray AOCODOCIDIC2D2 and light @AoB.

A, C, D, C2D2. Ray A. BoA, BLD
, C2D.

As in, things that have passed through the paths of the gods are included, and all of these interfere with each other. Let the amplitude reflectance of the parallel plane plate 25 and the air be r1, and the amplitude transmittance be t. Also, A for wavelength type light
. If the optical length of Bo is (refractive index x length))5t(λ), then for example, light MA. C.O.D.

Amplitudes of C, D, C, D, and point A. The phase difference with
......Equation (1) Phase difference = T (2PI o,
+ 5 t(λ))...Equation (2). (
The negative sign of -r in equation 1) is because when the light entering the parallel plane plate 25 from the air is reflected at point A, the phase changes by π. The amplitude and phase difference are as follows when the amplitude and phase difference of EoE, E, ......En are investigated using complex numbers.

......Equation (6) is obtained. Energy reflectivity R,=,2. Assuming energy transmittance T = t2, Jo = IEO12 = 2 几T2(1+(m(-T(2)
0, P, -20, P, )))...(8) formula% formula%)...(9) formula, and Jo, J, --Jn are all optical path differences ( 20,
P, -20t Pt ), and t(λ)
It turns out that it doesn't depend on the situation.

This is because every ray that gathers at point Dn passes through the parallel plane plate 25 the same number of times (2n+1), so the 7th
Unlike the conventional example shown in the figure, there is no need to take the trouble to arrange the correction plate 8 made of the same material and the same thickness on the opposite side of the substrate 4 on which the semi-transparent membrane 5 is formed. 'C1 parallel plane plate 2
5 and a retroreflector such as a corner cube reflector 23, 24, the phase is corrected and an interferometer capable of interfering with a constant optical path difference can be obtained. FIG. 9 shows what happens if the interferometer is configured with plane mirrors 9 and 10 and parallel plane plate 25 without using a retroreflector. In FIG. 9, for example, the output Eo has rays All Co Ao B.

. Ray A. Bt Dt Bt Ao Be, Mr. Ray B,
Includes A, C, A, B, visual B0, etc. However, the phases of Kowara's light are all different. For example, output E
Calculating o, refracted light A. The refraction angle of Bo is ψ +・・・・・・・・・・・・・・・
・α [Equation......Equation (11), where multiple beams of light with different phase differences interfere.

Among the lights reflected by each of the fixed reflection f@lo and the movable reflecting mirror 9, the strongest one is retained and approximated a...
・It will be Type 02. Calculating the energy, So# R, T 2 (1-1-T2+2Tcus(-”
-(2B, Possible -2nds7λ λ ・+2](λ)+1)) ・・・・・・・・・
...(I3) formula, optical path difference 2 B+Dt -2An
shows interference of Co + 21(λ)+2, but 1(λ)
remains in the optical path difference, and even if an approximation like Equation 02 is used, the phase is not corrected. E, E,...
It can be similarly proven that the phase of −・ is not corrected. Therefore, an interferometer cannot be constructed with the plane mirrors 9 and 10 and the parallel plane plate 25, and as shown in FIG. 2 of the embodiment of the present invention.
Retroreflectors 23, 24 are required in place of this planar chain 10°9.

Incidentally, although the incident light is shown by a single line 21 in FIG. 2, in the conventional two-beam interference spectrometer shown in FIG.

Therefore, when considering ray 21, EOEl "'t
. . . are independent and mutual interference is not a problem, but it becomes a problem when parallel light beams are incident. FIG. 3 shows a case in which parallel light beams are incident on the present invention. In FIG. 3, one wavefront W of the incident light 21 is formed on a plane-parallel plate 25. Fixed corner cube reflector 23. Due to the action of the movable corner cup reflector, the wave surface W is divided and interfered. W.I.W.
...and becomes the output light of the interferometer. WoW,
・・・・・・Without consideration of mutual interference, the intensity of each luminous flux when turned off is the incident energy % 1 (!: [, and E expressed by the third equation and @7 equation.E, E, ・The wavefront W. W, W, ... are each emitted with a deviation of a perpendicular to the direction of travel of the light.

The thickness of the plate is d, the angle of incidence of the incident ray 21 is θ, and the angle of refraction is ψ
♂Then, this interval a is a='l d tanψ■θ ・・・・・・
...It becomes α4 formula. When the wavefront moves in a direction perpendicular to the direction of travel, the extent to which it is coherent depends largely on the type of light and the surface condition of the collimating reflector 3.0 If the incident light is 17-the light, Wave surface W. is coherent over almost the entire surface, and if there is a place where the cursor and WI overlap, interference will occur there, but in the case of a normal light source, the lateral coherence is small, and when collimated with a polished concave note, the middle red ISO against external light.

Interference is sufficiently lost with a width of about M. For visible light, even less is required. Recently, aspherical mirrors with a surface roughness of about 30M can be made by cutting aluminum surfaces.
In this case, a deviation of about ±100M is sufficient to eliminate interference. On the other hand, by using a collimating reflector 3 with an appropriate surface roughness, it is possible to limit the interference in the lateral direction, and by increasing the thickness of the parallel plane plate 25, the incidence of the light ray 21 can be limited. It can also be restricted by increasing the angle θ.

From the above, EoE! E! can be treated as an independent light a, so the interferometer according to the present invention has an optical path difference of 2P, 0.
-2'p, o, can be used to interfere.

Regarding the amplitude of the interference signal expressed by the eighth and ninth equations, consider the case where germanium (Ge) is used for the parallel plane plate 25. Ge has T = 0.0 for red light with a wavelength of 20μ.
It is about 3. If R=0.7 without considering absorption, then J=J, +J, +...... Kasumi formula % formula % (1 (-> −(20+ P+ −20t Pt ) ) )
・・・==−Qe formula=2几T2(1+σjige
2π −−1□−R,□) (1+Q)l(2(2
01F1 20! P! )))・・・・・・・・・(I
7) Formula % Formula %) :) ......It becomes formula 081. 1%=Q, 7%p=Q, Calculating the formula from 0 to 3, the strength of interference = 0.30 Tonat T, R=Q
, 7°T = 0.3° (7) Maximum efficiency (2RT) 0
．． 420) 71%. Wave surface w1w!・・・・・・
is rejected because of Zuwaa, but the expression side! Term 1 (wave surface Wo
) alone results in an interference strength of 0.13, and at least 60% of the maximum efficiency is corrected. Ge has a wavelength of 2μfn~1
For oμm infrared light, T = about 0.5 is almost ideal. If 几 = 0.5, 2RT" = 0.25, which is equal to the maximum efficiency and there is no problem. The amplitude of the interference signal is actually different from the above equation. That is, the optical path difference is 20 Ips.
As 2 ot pt increases, the amount of coherent light in normal light decreases, resulting in a decrease in output. However, this is exactly the same for the prior art, and as mentioned above, it can be said that there is no problem with the magnitude of the interference signal.

An embodiment in which the interferometer according to the present invention is applied to the two-beam interference spectrometer shown in FIG. 7 is shown in FIG. 1. When compared with FIG. 1, the difference is clear.

Firstly, in the present invention, the cylindrical blunt is replaced with a retroreflector. As mentioned above, when using a plane mirror, the error in the direction of light reflection and the error in the optical path difference due to the slight inclination of the mirror have a significant negative effect on the measurement, so the bearing in the propulsion device H1x is generally equipped with air (not shown). bearings are used,
Further, an elevation adjustment device is attached to the fixed-side plane mirror to periodically adjust the elevation angle of the fixed-side plane mirror. On the other hand, the movable retroreflector 9 and the fixed retroreflector 10 have a property that the reflection direction and the optical distance between the retroreflector and the semi-transparent membrane do not change even if the retroreflector is tilted. (Air bearings require a dry air supply device in addition to the bearing body); ordinary ball bearings are sufficient. Particularly in high-resolution interferometric spectrometers, that is, with long optical path differences, retroreflectors are used to stabilize performance.1 Even in normal-resolution spectrometers, this reduces cost, reduces size, and improves stability.

These retroreflectors 9 and 10 are used instead of plane mirrors due to a number of advantages.

Second, the present invention does not require the correction plate required in the conventional example shown in FIG. Thereby, the material cost and polishing cost of the beam splitter 19 can be reduced. Furthermore, conventionally, a high-resolution spectrometer has a ±
Although accuracy of about 10 μm was required, there is no longer any need to match the thickness of the two sheets as a set. The effect of the present invention is even greater because the work of making the thickness uniform requires repeated polishing and measurement, which takes a considerable amount of time.

Furthermore, in the conventional case, it is necessary to insert a spacer between the substrate 4 and the correction plate 8 and assemble them into one holder. At this time, since an air layer is formed between the substrate 4 and the correction plate 8, multi-beam interference occurs between the substrate 4 and the correction plate 8, and a specific wavelength is often absorbed. In this case, the substrate 4 and correction plate 8 must be assembled with a slight inclination. In the present invention, the above-mentioned assembly work is not required at all,
It works just by fitting it into the holder, and there is no need to worry about multi-beam interference. This also reduces costs further.

Thirdly, in the present invention, there is no need to evaporate the semi-transparent film 5; the evaporation operation is normally performed while heating the substrate 5.

For example, when depositing a Ge semipermeable film on KBr, the higher the temperature of the substrate 5, the higher the quality and strength of the film.

If the temperature is completely raised without raising the temperature, the surface precision of the polished KBr will deteriorate, which is quite difficult to control. Since such a vapor deposition process is not required at all, the cost of the beam splitter 19 can be further reduced. Not requiring a semipermeable membrane has advantages not only in terms of cost but also in terms of performance. For example, a conventional beam splitter in which a semi-transparent film of Ge is deposited on KBr utilizes the interference of the Ge desert, but the wavelength range of light that can be split is limited by the thickness of the thin film. For example, KBr is 400C1
11-1 (infrared light) to 30000 CIL-' (visible)
(4 Q Q c with Je thin film)
If you were to make a beam splitter from rIL-1, you would only be able to make one with a maximum length of about 50,007 m.

However, according to the invention, the entire transmission range of KBr light can be utilized. However, the refractive index of KBr is 1 in this region.
．． 5 to 1.7, and the reflectance ratio in the case of normal incidence is several orders of magnitude, so it is necessary to increase the reflectance by increasing the angle of incidence, but from 400[-1 to 30000α-
It is possible to make an effective beam splitter up to 1. There is no need to be particular about KBr as the material; for example, thallium iodide (KR8-5) with a high refractive index or thallium bromochloride (
KR8-6) allows the angle of incidence to be reduced.

If it is impossible to increase the incident angle, vapor deposited films 34 and 35 may be formed on both sides of the parallel plane plate 25 as in another embodiment shown in FIG. Although the benefits resulting from the lack of need are lost, the benefits resulting from the lack of need for a corrector plate are still valid.

Compared to the conventional method in terms of cost, it is necessary to evaporate on one side of the substrate 4 shown in Fig. 7, but if the jig is devised and the vacuum of the evaporator is not broken during evaporation, it can be evaporated on both sides. It won't be a big cost increase.

In the above embodiment, germanium and thallium bromoiodide were used as the material for the parallel plane plate, but the present invention is not limited to these materials. Dielectric materials can be used. In addition, the retroreflector 23
Or 24.

In the embodiment, a corner cube reflector was used as shown in FIG. 2, but it goes without saying that other retroreflectors may be used.

For example, the corner cube prism shown in FIG. 10(a),
A retroreflector called a cat's eye reflector in Figure 10(b), a mirror made of two plane mirrors glued together at right angles as shown in Figure 10(C), or a triangular prism with two sides at right angles, etc. can also be used. A corner cube prism is similar to a corner cube reflector, and has recently been widely used in distance finders for surveying using lasers.

The interferometer according to the present invention can be applied not only to interferometric spectrometers but also to other applications. Figure 6 is an example of application to a distance measuring device. In FIG. 6, the X-Y stage 36 is moved in the direction of the arrow by a drive motor (not shown). X-coordinate retroreflector 37. ? The coordinate retroreflector 38 is of the type shown in FIG. 10(C) and is attached to the XY stage. A laser beam 40 emitted from a laser light source 39 is split into two by a beam splitter 41, one of which is used to measure the X coordinate.

The other is used to measure the X coordinate. Since the X coordinate and the method of measuring the X coordinate are the same, only the X direction will be explained. The light separated at point A by the beam splitter 42 according to the invention is reflected by the X coordinate retroreflector, and the other light is reflected by the reference retroreflector 43 to cause interference at point B of the beam splitter 42. , the light reflected after interference is sent to the length measurement detector 44, and the light transmitted after interference is sent to the direction detector 4.
Detected at 5. The laser beam 40 is linearly polarized light and has a P component and eight components relative to the semi-transparent membrane surface on the beam splitter 42, but the 1/4 wavelength plate 46 delays the P component by 1/4 wavelength, and a polarizing plate 46 delays the P component by 1/4 wavelength. 47, the direction detector 45 detects the P component. The S component interferes without being out of phase, and is detected by the detector 44 by the action of the polarizing plate 48. In this way, the outputs of the detectors 44 and 45 are out of phase by about λ/4, and the direction can be detected using the same principle as a rotary encoder. Now, the important point at this time is the beam splitter 4.
2, the reference retroreflector 43 does not move. If these positions move during measurement, the detector 44 naturally
An output as if the stage 36 had moved by that amount is output, resulting in incorrect measurement. Since laser light is monochromatic, chromatic dispersion due to materials is not a problem. However, if a conventional beam splitter with the correction plate 8 removed is used instead of the beam splitter 42, the optical path difference on one side changes due to thermal expansion of the material, so an expensive material with a small expansion coefficient is required. . However, when a correction plate is inserted, the above-mentioned problems of the correction plate, such as errors in thickness and cost, occur. Therefore, when using the beam splitter 42 according to the present invention, the effect of thermal expansion can be completely corrected if the beam splitter 42 is made to expand toward the B side based on the 5 points A side. Moreover, since the configuration is simple, the above-mentioned advantages can be utilized as is.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, light split on one side is split by using a beam splitter consisting of one parallel plane plate made of a light-transmitting material and a - pair of retroreflectors. Since we configured the interferometer to interfere on the other side,
Before the two split lights interfere, they both pass through the substrate the same distance, making it possible to have the same correction effect as the correction plate that was required in the past. As a result, there is no longer a need for a correction plate or vapor deposition of a semi-permeable membrane, which were required in the past, making it possible to improve not only cost but also performance.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an interferometric spectrometer to which an interferometer according to the present invention is applied, FIGS. 2, 3, and 4 are block diagrams showing embodiments of the interferometer according to the present invention, and FIG. FIG. 6 is a schematic diagram showing an example of a retroreflector, FIG. 6 is a block diagram showing another example of a device using an interferometer according to the present invention, and FIG. 7 is a diagram showing a conventional interferometry device using an interferometer. 8 is a schematic diagram showing a conventional beam splitter, FIG. 9 is a block diagram showing the action of a beam splitter according to the present invention when a plane mirror is combined, and FIG. 10 is a diagram showing the action of a retroreflector. It is a schematic diagram for explaining. 4: Substrate, 5: Semi-transparent film, 8: Correction plate, 19: Beam splitter, 23: Fixed retroreflector, 24: Movable retroreflector, 2
5: Semi-permeable membrane, 27: Semi-permeable membrane. Eo Et Ez 3rd grade, 4th figure, 5th figure, Katsu υ

Claims (9)

[Claims] (1) An interferometer characterized by having a beam splitter made of a plane-parallel plate that is sufficiently thicker than the wavelength of the light to be interfered with, and two retroreflectors arranged a predetermined distance from each side of the splitter. . (2) An interferometer according to claim 1, characterized in that the material of the parallel plane plate is a semiconductor material. (3) An interferometer according to claim 2, characterized in that the semiconductor material is germanium. (4) An interferometer according to claim 2, characterized in that the semiconductor material is silicon. (5) An interferometer according to claim 2, characterized in that the semiconductor material is potassium arsenide. (6) An interferometer according to claim 1, characterized in that the material of the parallel plane plate is a dielectric material. (7) An interferometer according to claim 6, characterized in that the dielectric material is selenium. (8) An interferometer according to claim 6, characterized in that the dielectric material is thallium bromoiodide. (9) An interferometer according to claim 6, characterized in that the dielectric material is thallium bromochloride.