JPH09318311A - Interferometer system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce influence on measurement precision even when an optical element oscillates or moves by measuring relative optical path length change of two light fluxes from the output of a photodetector. SOLUTION: The coherent light flux incident on a light division/mixture device 11 is reflected on a polarized light flux division/mixture surface 21, to be divided into the first optical path 31 of s-polarization proceeding to the first reflector 81 and the second optical path of p-polarization which transmits the mixture surface 21. A circular polarization light flux reflected on the reflector 81 becomes p-polarization light flux, and after re-entering the mixture device 11, transmits the mixture surface 21. Transmission p-polarization light flux transmits a quarter wavelength board 52, to be a circular polarization light flux, and then reflected on the second reflector 82, to become s-polarized light flux, and after entering the mixture device 11, reflected on the mixture surface 21. The reflection light flux is almost coaxial with p-polarized light flux passing through the second optical path, and enters a photodetector 2, and its electric signal is inputted in a phase meter. The phase meter measures relative optical path length change of two light fluxes divided at the mixture device 11, for detecting movement amount of the reflectors 81 and 82.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer system for splitting a coherent light beam and measuring a relative change in optical path length of the split light beam.

[0002]

2. Description of the Related Art Among various methods for measuring length, a light wave interferometer with a scale of light wavelength is an excellent method capable of obtaining high resolution and high accuracy. Until around 1970, interferometers were used only for specific research institutes or special inspection devices because of the high flatness required for the optical elements that make up the interferometer and the need for skill in optical adjustment. There was little to be done. However, it is now possible to configure an interferometer with relative ease, and many types of products have come to the market.

The structure of a general interferometer will be briefly described with reference to FIG. A laser beam 101 emitted from a laser light source 100 is split by a beam splitter 102.
The divided light beams are reflected toward the reference reflector 105 and the moving reflector 106, respectively. The light beams reflected by the reference reflector 105 and the moving reflector 106 enter the beam splitter 102 again and interfere with each other. The interfering light flux is detected by the photodetector 107. Photodetector 1
From the interference signal detected at 07, the relative movement amount between the reference reflector and the moving reflector is detected with the wavelength of light as a scale. Strictly speaking, the luminous flux 10 guided to the reference reflector 105 side
It is possible to detect the relative difference between the change in the optical path length of the light beam 3 (hereinafter referred to as the reference light beam) and the change in the optical path length of the light beam 104 (hereinafter referred to as the measurement light beam) guided to the movable reflector 106 side. As a method of detecting an interference signal, a method of photoelectrically detecting and counting an interference fringe array generated by the movement of the moving reflector 106, a method developed at the National Physical Laboratory in the United Kingdom, or a product of Hewlett-Packard Company in the United States is used. The adopted optical heterodyne method and the like are widely known. Further, the structure of the interferometer is not limited to the detection method of these interference signals, and various structures are known, from a simple structure to a complicated structure with improved stability and resolution.

[0004]

However, the conventional interferometer has a problem that the measurement accuracy is lowered when each optical element moves independently due to vibration or the like. FIG.
An area surrounded by a dotted line A of 5 is shown in FIG. In FIG. 16, the beam splitter 102 is a moving reflector 1 due to external influences.
It is a figure at the time of moving to the 06 side by the distance d. FIG.
In FIG. 6, what is indicated by the solid line is the position of the beam splitter 102 and the light beam before the movement, and what is indicated by the dotted line is the position of the beam splitter 102 and the light beam that are moved by the vibration. It is assumed that the position of the laser light 101 emitted from the laser light source 100 does not change. As is clear from FIG. 16, the reference light flux 10 guided to the reference reflector 105 side.
The optical path length of 3 does not change even if the beam splitter 102 moves, but the measurement light beam 10 guided to the moving reflector 106 side.
The optical path length of 4 changes by 2d between the time when the beam is emitted from the beam splitter 102 and the time when the beam is incident on the beam splitter 102 again. That is, if the beam splitter 102 moves due to a disturbance such as vibration when measuring the moving amount of the moving reflector 106, even if the moving reflector 106 does not move, the output of the system of FIG. Since 106 is moved, there is a problem that the measurement accuracy is lowered. Even if the beam splitter 102 moves to the reference reflector 105 side, the optical path length of the measurement light beam also changes, and the measurement accuracy decreases.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an interferometer system that has little influence on the measurement accuracy even if an optical element vibrates or moves due to the influence of disturbance or the like. To do.

[0006]

Therefore, in the interferometer system of the present invention, a light source for supplying a coherent light beam, a splitting device for splitting the light beam from the light source into two light beams, and a splitting device are arranged so as to face each other. And a pair of first and second reflectors that are separated from each other, and reciprocating optical path forming means for making one round trip of one of the light beams split by the splitting means, and interference between one and the other of the light flux split by the splitting means. It has an interference optical system and a photodetector for detecting the interfering light beams, and measures the relative change in the optical path length of the two light beams from the output of the photodetector (claim 1).

Further, in this case (claim 1), the light flux which has passed through the reciprocal optical path forming means is reflected so as not to be parallel and coincident with the optical axis of the light flux, and the reflected light flux is incident on the reciprocal optical path forming means again. An optical path transfer means arranged so as to allow the optical path may be provided (claim 2). Further, in these cases (claim 1 or 2), the reciprocating optical path forming means is arranged so that the other light beam reciprocates the same number of times as one light beam reciprocates the first and second reflectors. It further has a pair of third and fourth reflectors, and the optical path of the other light beam that reciprocates between the third and fourth reflectors and the optical path of one light beam that reciprocates between the first and second reflectors are in close proximity. It may be an optical path (claim 3).

Further, in these cases (claim 1, 2 or 3), the splitting means is a polarization beam splitter, and the round-trip optical path forming means is arranged between the polarization beam splitter and the first and second reflectors, respectively. You may further have the 1/4 wavelength plate which was carried out (Claim 4). Further, in these cases (claim 1,
2, 3 or 4) may have a plurality of reciprocating optical path forming means (claim 5).

Further, in these cases (claims 1 to 5),
One of the light beams divided by the dividing means may make two or more round trips between the first and second reflectors (claim 6).

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. FIG. 1 is a schematic configuration diagram showing an interferometer system according to a first embodiment of the present invention. The system of FIG. 1 has a laser light source 1, a round-trip optical path forming means 41, and a photodetector 2. In addition, the round-trip optical path forming means 41 is the light splitting / mixing device 1
1, 1/4 wave plate 51, 52, first reflector 81 and second
It has a reflector 82. The laser light source 1 supplies a coherent light flux, and for example, a gas laser represented by a helium neon laser, a semiconductor laser, or the like can be used. Further, in the present embodiment, a polarization beam splitter in which two right-angle prisms are combined is used as the light dividing / mixing device 11, and flat reflectors are used as the first and second reflectors. A photodiode or the like can be used as the photodetector 2, and the light incident on the photodetector 2 is photoelectrically converted and output as an electric signal.

The coherent light beam incident on the light splitting / mixing device 11 is reflected by the polarization light beam splitting / mixing surface 21 of the light splitting / mixing device 11 and is directed toward the first reflector 81.
And a second optical path of p-polarized light that passes through the polarized light beam splitting / mixing surface 21. A quarter-wave plate 51 is arranged in the first optical path 31, and the s-polarized light flux transmitted through the quarter-wave plate 51 becomes a circularly-polarized light flux, which is incident on the first reflector 81 and reflected. It The circularly polarized light beam reflected by the first reflector 81 passes through the quarter-wave plate 51 again, becomes a p-polarized light beam, and again enters the light splitting / mixing device 11, and then is polarized by the light splitting / mixing device 11. The light is transmitted through the divided mixing surface 21. Transparent p
The polarized light flux becomes a circularly polarized light flux by passing through the quarter-wave plate 52 arranged between the light splitting mixer 11 and the second reflector 82, enters the second reflector 82, and is reflected. It The circularly polarized light beam reflected by the second reflector 82 passes through the quarter-wave plate 52 again to become an s-polarized light beam, which is incident on the light-splitting / mixing device 11 and then split by the light-splitting / mixing device 11. It is reflected by the mixing surface 21.

When the reflected light flux is arranged so that the light fluxes incident on the first and second reflectors are perpendicular to each other, the reflected light flux becomes substantially coaxial with the p-polarized light flux passing through the second optical path and enters the photodetector 2. The two light beams do not interfere as they are because they have different polarizations, but they interfere with each other by disposing a polarizer (not shown), a quarter-wave plate or the like in front of the photodetector 2. This interference light is guided to the photodetector 2, and its intensity is output as an electric signal. The electric signal output from the photodetector 2 is input to a phase meter (not shown). The phase meter detects the relative movement amount of the first reflector 81 and the second reflector 82 by measuring the relative change in the optical path length of the two light beams split by the light splitting / mixing unit 11.

In this embodiment, the relative movement amount of the first reflector 81 and the second reflector 82 is measured by using the interferometer system of FIG. It is also possible to arrange an object to be measured between the light division mixer 11 and measure its refractive index. Further, in the present embodiment, the homodyne interferometry is used as the method for detecting the interference signal, but the heterodyne interferometry or the like used by Hewlett-Packard Company mentioned above may be used.

In this embodiment, flat reflecting mirrors (plane mirrors) are used as the first and second reflectors, but retroreflectors such as corner cube prisms and halo cube mirrors may be used. Further, although the polarization beam splitter is used for the light dividing / mixing device 11, the present invention can be achieved by using a beam splitter. In this case, the quarter-wave plates 51 and 52 used in this embodiment are unnecessary.

As described above, according to the present embodiment, even if the polarization beam splitter 11 moves in the vertical direction on the paper surface, the optical path lengths that affect the light fluxes traveling in the first optical path and the second optical path, respectively. The changes are the same and do not affect the measurement results of the interferometer system, and therefore do not affect the measurement accuracy. Further, even if the polarization beam splitter 11 moves in the left-right direction on the paper surface, similarly, since the first optical path and the second optical path are not affected, the measurement accuracy is not affected. Further, even when the emission position of the laser light flux emitted from the laser light source 1 changes in the left-right direction of the paper surface, the measurement accuracy does not decrease for the same reason.

FIG. 2 is a schematic configuration diagram showing an interferometer system according to a second embodiment of the present invention. The system of FIG. 2 is almost the same as that of the first embodiment except that the optical path transfer means 71 is arranged. Therefore, the same components as those of the first embodiment will be described with the same reference numerals. Is omitted. The optical path transfer means 71 may be anything such as a corner cube prism as long as the optical axis of the light beam incident on itself is parallel to the optical axis of the reflected light beam. However, when the light flux is separated by using the polarized light as in the present embodiment, it is preferable to use an element in which the polarization plane of the incident light flux and the polarization plane of the reflected light flux do not change.

The light flux emitted from the laser light source 1 enters the optical path transfer means 71 through the same optical path as the two light fluxes directed to the photodetector 2 of the first embodiment. The light flux passing through the second optical path 32 is the p-polarized light flux emitted from the laser light source 1 and transmitted through the light division mixer 11, and the p-polarized light flux is the optical path transfer means 71.
After being reflected by, the light passes through the light dividing / mixing device 11 and travels toward the photodetector 2. The light flux passing through the third optical path 33 is an s-polarized light flux that is emitted from the laser light source 1, is reflected by the light division mixer 11, and passes through the first optical path 31. This s-polarized light beam again enters the reciprocal optical path forming means 41 and is reflected by the light division mixer 11. After that, the reflected light flux is reflected by the second reflector 82 and the first reflector 81, and again reflected by the light splitting / mixing device 11 as the s-polarized light flux, and travels toward the photodetector 2. In this way, the light splitting mixer 11 to the photodetector 2
The two luminous fluxes heading for interfere with each other in the same manner as in the first embodiment and are detected by the photodetector 2.

In the system of FIG. 2, by providing the optical path transfer means 71, the adjustment range of the optical element can be widened as compared with the first embodiment. Hereinafter, that point will be described. It is assumed that each optical element is ideal. First, consider a system that does not use the optical path transfer means 71 described in the first embodiment. Here, the first
Consider a case where the reflector 81 is slightly rotated about an axis perpendicular to the paper surface. Then, the light passing through the first optical path 31 does not vertically enter the reflecting surface of the first reflector 81. Therefore, finally, the optical axes of the two light beams traveling from the light splitting / mixing unit 11 to the photodetector 2 have a certain angle. However, since the present system observes the change in the optical path length of the two light fluxes by causing the two light fluxes to interfere with each other, the measurement accuracy is reduced unless the two light fluxes are substantially parallel to each other. That is, when the optical axes of the two light fluxes have an angle, the longer the distance between the two light fluxes reaching the photodetector 2, the smaller the overlap of the two light fluxes and the lower the measurement accuracy. Therefore, the system of FIG. 1 needs to perform optical adjustment with high precision.

Next, consider the system of the present embodiment shown in FIG. For comparison with the first embodiment, again, consider the case where the first reflector 81 is slightly rotated. By providing the optical path transfer means 71, the number of times the light flux traveling in the first optical path 31 passes through the reciprocal optical path forming means 41, that is, between the first reflector 81 and the second reflector 82 before and after the optical path transfer means 71. The number of round trips is the same. As described above, the optical path transfer means 71 has the optical axis of the light incident on itself and the optical axis of the reflected light parallel to each other, and thus the first reflector 81.
The inclination of the optical axis due to the rotation of the
By going through 1 (by going through the opposite optical path)
Offset. At this time, the horizontal displacement (parallel displacement) of the optical axis that occurs
It is easy to neglect. Therefore, the second
The system of this embodiment simplifies the optical adjustment of the first reflector 81. Further, in the system of FIG. 2, the light flux travels back and forth twice between the first reflector 81 and the second reflector 82 (double path), so that the system has a high resolution.

In most cases where a flat reflector is used as the reflector, there is a problem that the difficulty of optical adjustment of the optical elements constituting the interferometer system is increased, or when the reflector is arranged on the moving body. However, if the accuracy of the linear motion of the moving body is poor, the interference signal may not be detected. Also, retroreflectors are usually more expensive than flat reflectors. According to the present embodiment, even when a flat reflector is used as the reflector, the above-mentioned problems that are seen in many conventional interferometer systems are not caused by making an even number of round trips between the flat reflectors. An inexpensive interferometer system can be constructed. Of course, even if a retroreflector is used as the reflector, the main effect of the present invention is not impaired at all.

Similarly, it is possible to reduce the deterioration of the measurement accuracy due to the rotation of the second reflector 82, the variation of the emission angle of the light beam emitted from the laser light source 1, the rotation of the light division mixer 11, and the like. Similarly, the first and second reflectors 81,
As for the motion accuracy of 82, in the first embodiment, high motion accuracy is required so that the reflecting surface of the reflector does not shift.
In the second embodiment, the measurement accuracy does not decrease even with low motion accuracy.

The system shown in FIGS. 3 and 4 is a modification of the second embodiment of the present invention, in which the number of optical path transfer means optically coupled to the reciprocal optical path forming means 41 is changed and the first and second reflections are performed. By increasing the number of round trips between instruments, a system with higher resolution is constructed. FIG. 3 shows an optical path transfer means (71, 7).
2, 73) are provided, and the first reflector 81 and the second reflector 8 are provided.
It is configured to make four reciprocations between the two. In FIG. 4, seven optical path transfer means (71 to 77) are provided, and the first reflector 81 is provided.
And the second reflector 82 are reciprocated eight times. Although illustration is omitted, according to the present invention, it is easy to change the number of times of reciprocating between the first and second reflectors by providing the optical path transfer means other than those shown in FIGS. It can be appropriately selected according to the size and resolution of the interferometer. Further, in the above description, the number of the optical path transfer means is set to the required maximum number for the sake of easy understanding.
As shown in FIG. 3, one of the plurality of optical path transfer means shown in FIGS. 3 and 4 may be combined with one optical path transfer means. FIG.
Is an example in which the functions of the optical path transfer means 71 and 73 shown in FIG. FIG. 6 shows an example in which the functions of the optical path transfer means 71, 73, 75, 77 of FIG.

FIG. 7 is a schematic configuration diagram showing an interferometer system according to a third embodiment of the present invention. FIG. 7 shows that the quarter-wave plate 53 and the third and fourth reflectors 83 and 84 are added to the interferometer system of FIG. 3 described in the second embodiment of the present invention.
The configuration is such that a differential signal between two light fluxes, each of which makes two round trips between a pair of reflectors, is detected. Since other configurations are similar to those of the interferometer system of FIG. 3, similar components are designated by the same reference numerals, and description thereof will be omitted.

FIG. 7 shows an embodiment in which a differential signal, which has the same size as that of FIG. 3 and which makes two round trips between two pairs of reflectors, is detected. The quarter-wave plate 53 is also used for converting the plane of polarization of the light flux by 90 ° by reciprocating the light flux, similarly to the quarter-wave plates 51 and 52. Therefore, the two light fluxes from the light splitting / mixing device 11 to the optical path transfer means 71 are the same as those in the system of FIG. 3, but by disposing the quarter wavelength plate 53, the p-polarized light flux becomes an s-polarized light flux. Conversely, the s-polarized light beam becomes a p-polarized light beam. That is, by arranging the quarter-wave plate 53, the optical path transfer means 7 is transmitted through the light dividing / mixing device 11.
The light flux heading for 1 is reflected by the optical path transfer means 71,
It is reflected by the light division mixer 11. The reflected light flux passes through the quarter-wave plate 52 and is reflected by the fourth reflector 84, and the quarter-wave plate 52, the light division mixer 11, and the quarter-wave plate 51 are reflected.
And is reflected by the third reflector 83. After that, this light flux is reflected by the light splitting mixer 11 and the optical path transfer means 72,
The light is again incident on the light division mixer 11, and is reflected toward the third reflector 83. The luminous flux heading for the third reflector 83 is the third
After being reflected by the reflector 83, passed through the quarter-wave plate 51, the light division mixer 11, and the quarter-wave plate 52 and reflected by the fourth reflector 84, the light division mixer 11, the optical path transfer means. 73,
It passes through the light splitting / mixing device 11 toward the photodetector 2. On the other hand, in the system of FIG. 3, the light flux reflected by the optical path transfer means 71 and then by the light splitting / mixing surface 21 passes through the light splitting / mixing device 11 in the system of the present embodiment. The transmitted light flux is reflected by the optical path transfer means 72, transmitted through the optical division mixer 11 and reflected by the optical path transfer means 73, and then the optical division mixer 1
It is reflected at 1 and goes to the second reflector 82. Second reflector 8
The light flux heading for 2 is reflected by the second reflector 82, passes through the light division mixer 11, and is reflected by the first reflector 81.
The light is reflected by the light division / mixer 11 and travels to the photodetector 2.

In this way, the two light beams directed to the photodetector 2 interfere with each other in the same manner as in the above-described embodiment and are detected by the photodetector 2. The third embodiment is an interferometry system that detects a differential signal between two pairs of reflectors. By making the optical paths of the two luminous fluxes split by the optical splitter / mixer 21 substantially common, refraction on the optical path is performed. Since the optical path length changes given to the two light fluxes can be made substantially the same due to the rate fluctuation and the like, the measurement error can be reduced as compared with the second embodiment, and stable measurement can be performed. Further, the size of the device does not increase as compared with the second embodiment.

FIG. 8 shows the interferometer system of FIG. 6 described in the second embodiment, and the quarter-wave plates 54 and 55 and the third and fourth wavelength plates.
The reflectors 83 and 84 are added to detect a differential signal between two light fluxes that make four round trips between two pairs of reflectors. Since the optical path is clear from the description of FIGS. 6 and 7, detailed description thereof will be omitted.
The system shown in FIG. 6 has the same stability as the system shown in FIG. 7 while maintaining the high resolution of the system shown in FIG.

Although not shown, according to the present invention, FIG.
The number of round trips between the two pairs of reflectors can be set arbitrarily by providing the number of optical path transfer means other than those shown in FIG. 8 and the quarter wavelength plate, and the size and resolution of the interferometer can be appropriately selected. is there.
In the above description, the number of optical path transfer means is set to the necessary maximum number for easy understanding. However, for example, as shown in FIGS. 9 and 10, the plurality of optical path transfer means shown in FIGS. It is also possible to use some of the means as one optical path transfer means and change the insertion position of the quarter wavelength slope appropriately. FIG. 9 shows the functions of the optical path transfer means 71 and 73 of FIG.
The quarter wave plate 56 is used instead of the quarter wave plate 53. In addition, FIG.
The function of the optical path transfer means 71, 73, 75, 77 of FIG.
A quarter wave plate 57 is used in place of 4, 55.

As described above, the interferometer system according to the third embodiment of the present invention is an interferometer system for detecting a differential signal between two pairs of reflectors, and two light beams split by an optical splitter / mixer. By making the optical paths of the two to be substantially common, the stability can be significantly improved, and at the same time, the resolution can be maintained without significantly increasing the size and reducing the number of round trips between the reflectors.

FIG. 11 is a schematic configuration diagram showing an interferometer system according to a fourth embodiment of the present invention. In addition, the arrow in the figure indicates the traveling direction of the light flux. The interferometer system shown in FIG. 11 is characterized in that a reciprocal optical path forming means 42 is provided as compared with the interferometer system shown in FIG. 2, and other configurations are similar to those of the system of FIG. The same symbols are attached to the configuration and the description thereof is omitted. The reciprocating optical path forming means 42
Like the reciprocating optical path forming means 41, is composed of two quarter-wave plates 58 and 59, two reflectors 85 and 86, and the light splitting / mixing device 12, and has the same function.

That is, of the light beams emitted from the laser light source 1 and split by the light dividing / mixing unit 11 of the reciprocal optical path forming means 41, a pair of reflectors 81, 82 of the reciprocal optical path forming means 41.
The light flux that makes one round trip between the two enters the round trip optical path forming means 42, makes one round trip between the pair of reflectors 85 and 86 of the round trip optical path forming means 42, and then enters the optical path transporting means 71. The light flux entering the optical path transfer means 71 is reflected by the optical path transfer means 71, again enters the reciprocal optical path forming means 42, and reciprocates once between the pair of reflectors 85 and 86 of the reciprocal optical path forming means 42. Then, the light enters the reciprocating optical path forming means 41, travels back and forth between the pair of reflectors 81 and 82 of the reciprocating optical path forming means 41, and then goes to the photodetector 2. In addition, the light flux emitted from the laser light source 1 and transmitted through the light splitting / mixing device 11 has a reciprocal optical path forming means 4.
2 and is transmitted through the light splitting / mixing device 12 and then reflected by the optical path transfer means 71.
1 and goes to the photodetector 2. The two light beams heading for the photodetector 2 interfere in the same manner as in the above-described embodiment,
The intensity is detected by the photodetector 2.

Although not shown, the first reflector 81 and the sixth reflector 86 are arranged on the first moving body, and the second reflector 82 and the fifth reflector 85 are different from the first moving body. Even if it is arranged on another second moving body, the effect of the present invention is not impaired at all, and according to the present embodiment, the coherent measuring between the first moving body and the second moving body is performed. Since the light flux reciprocates at least four times, it is possible to remarkably improve the measurement resolution and accuracy of the change in the optical path length between the first and second moving bodies even if the signal division accuracy is the same. Further, with such a configuration, it is possible to artificially satisfy the Abbe principle. Of course, the first and second moving bodies can detect the change in the optical path length between the two moving bodies or the fixed body even when both or one of them is the fixed body, as in the case where both are the moving bodies. Further, in the present embodiment, since the polarization beam splitters are used as the light splitting mixers 11 and 12, four reciprocating movements between two moving bodies make it possible to compare the number of reciprocating movements to less than that. , It is possible to reduce the measurement error caused by the incompleteness of the light splitter. Further, according to the present embodiment, the distance between the first reciprocating optical path forming means 41 and the second reciprocating optical path forming means 42 can be set arbitrarily. Although illustration is omitted, if it is necessary to avoid an area that is physically unusable as an optical path or an area that is not desired to be used as an optical path and detour the optical path, a reflector or prism should be appropriately arranged. There is no problem even if the optical path is bent by bending the optical path, and the change in the optical path length between the first reciprocating optical path forming means 41 and the second reciprocating optical path forming means 42 changes between the first moving body and the second moving body. Does not affect the measurement of optical path length changes during

Further, although the system of FIG. 11 uses four plane reflectors 81, 82, 85 and 86, as shown in FIG. 12, retroreflectors 87, 88 such as corner cube prisms are used as the reflectors. 89 and 90 may be used. Although illustration is omitted, there is no problem even if a plane reflector and a retroreflector are selectively used as the reflector. The arrangements shown in FIGS. 11 and 12 are extremely useful for application to, for example, shape measurement of spherical optical elements and aspherical optical elements. In the case of such a measurement, two reciprocating optical path forming means are arranged at the optical axis symmetrical positions of the condenser lens and the lens to be measured so as to satisfy the Abbe's principle, and the first stage is arranged on the stage of the condenser lens. By fixing the reflector 81 and the sixth reflector 86 and disposing the second reflector 82 and the fifth reflector 85 on the stage of the optical element to be measured, the relative displacement between the condenser lens and the optical element to be measured can be measured. , The radius of curvature of the optical element is known.

The interferometer system of FIG. 13 further includes a round-trip optical path forming means 43 in addition to the interferometer system of FIG. 11, and each reflector is made into two reflectors (that is, one pair of reflectors is made into two pairs of reflectors). Is a modified example showing the interferometer system configured in (1). The reciprocating optical path forming means 43 is also the reciprocating optical path forming means 4
Two quarter-wave plates 60, 61 as well as 1, 42,
It is composed of two pairs of reflectors 87a, 88a, 87b, 88b and a light division mixer 13. In addition, the present system includes reflectors 81a, 81b, 86a, 86b, 88a, 88b.
Is fixed to the first moving body, and the reflectors 82a, 82b, 85
The a, 85b, 87a, and 87b are fixed to the second moving body, and the relative movement amount between the first moving body and the second moving body is measured. The first moving body and the second moving body are not shown.

Therefore, in the interferometer system of FIG. 13, by providing the round-trip optical path forming means 43, the number of round trips between the respective reflectors is increased as compared with the interferometer system of FIG. And can be improved. Of course, the number of the round-trip optical path forming means is not limited to that shown in FIG. 13, and the attenuation of the light passing through or reflecting the optical element does not exceed a predetermined amount and is increased within the coherence length of the light source. You can As a result, it is easily expected that the change in the optical path length between the reciprocating optical path forming means also increases.
In many conventional methods, there was a problem that the measurement accuracy deteriorates. However, according to the interferometer system of the present invention, the change in the optical path length between the reciprocating optical path forming means affects both the measurement light flux and the reference light flux. Since the same influence is exerted, the influence is canceled out as a result, so that the measurement accuracy is not deteriorated.

When it is difficult to arrange an interferometer system that satisfies the Abbe's principle, conventionally, for example, two measuring positions are provided on both sides of the measured position, and the arithmetic mean of the respective measured values is set. There are known methods for maintaining the measurement accuracy by, for example, satisfying Abbe's principle or Ebbenstein's principle, such as obtaining a value. As described above, according to the present embodiment, two or more reciprocating optical path forming means are provided as in the above-described conventional technique while maintaining high stability and resolution without making the structure of the optical element too complicated. In this way, it is possible to artificially satisfy the Abbe principle. Of course, the interferometer system according to the present invention can also be used as a plurality of independent interferometer systems that artificially satisfy Abbe's principle by adding a photodetector, as in the conventionally known technique. Is. An example is shown in FIG.

FIG. 14 is different from the interferometer system of FIG. 11 except that the flat reflectors 91, 92, 93, 94, the beam splitter 95, the reflector 96, and the photodetector 2a are provided. Since it is the same as the interferometer system of 1), the same reference numerals are given to the same configurations and the description thereof is omitted.
The system of FIG. 14 has a beam splitter 95 and a reflector 96.
By arranging and, the laser light flux emitted from the light source 1 is divided into two light fluxes having different optical paths. By arranging the four reflectors 91, 92, 93, and 94, each light beam shares some optical elements.
It goes through two interferometers.

Therefore, it is possible to realize the effect of being able to measure a larger number of optical path length changes. Further, although the light of one wavelength is used in FIG. 14, the measurement may be performed with the light of each of the plurality of wavelengths by combining the light of the plurality of wavelengths and the dichroic mirror. As described above, according to the interferometer system as shown in FIG. 14, it is possible to realize a large number of changes in the optical path length without complicating the configuration and increasing the size.

A photodetector is added as shown in FIG.
If you configure multiple independent interferometer systems, the output from each interferometer system and the relative relationship of the layout will be used to calculate
There is an advantage that the inclination of the moving body can be obtained.
In addition, in the first to fourth embodiments, all the optical paths are formed in the same plane as the paper surface so that the optical paths do not overlap on the paper surface in order to facilitate understanding. There is no problem even if they are arranged on a plurality of planes parallel to the paper surface.
It goes without saying that the first to fourth embodiments of the present invention may be combined as appropriate.

[0039]

As described above, according to the present invention, an optical system is not affected by a disturbance such as a structurally or thermally induced disturbance without complicating the structure of the optical system and increasing the size of the optical system. It is possible to provide an interferometer system that has little influence on measurement accuracy even if an element vibrates or moves.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration and a luminous flux traveling order of an interferometer system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration and a luminous flux traveling order of an interferometer system according to a second embodiment of the present invention.

FIG. 3 is a schematic configuration diagram showing a modified example of the interferometer system according to the second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram showing a modified example of the interferometer system according to the second embodiment of the present invention.

FIG. 5 is a schematic configuration diagram showing a modified example of the interferometer system according to the second embodiment of the present invention.

FIG. 6 is a schematic configuration diagram showing a modified example of the interferometer system according to the second embodiment of the present invention.

FIG. 7 is a diagram showing a schematic configuration and a luminous flux traveling order of an interferometer system according to a third embodiment of the present invention.

FIG. 8 is a schematic configuration diagram showing a modified example of the interferometer system according to the third embodiment of the present invention.

FIG. 9 is a schematic configuration diagram showing a modified example of the interferometer system according to the third embodiment of the present invention.

FIG. 10 is a schematic configuration diagram showing a modified example of the interferometer system according to the third embodiment of the present invention.

FIG. 11 is a diagram showing a schematic configuration of an interferometer system according to a fourth embodiment of the present invention and a luminous flux traveling order.

FIG. 12 is a schematic configuration diagram showing a modified example of the interferometer system according to the fourth embodiment of the present invention.

FIG. 13 is a schematic configuration diagram showing a modified example of the interferometer system according to the fourth embodiment of the present invention.

FIG. 14 is a schematic configuration diagram showing a modified example of the interferometer system according to the fourth embodiment of the present invention.

FIG. 15 is a schematic configuration diagram showing an interferometer according to a conventional technique.

FIG. 16 is an enlarged view for explaining a problem of a conventional interferometer.

[Explanation of symbols]

1, 100 ... Laser light source 2, 2a, 107 ... Photodetector 11, 12, 13, 102 ... Light splitting mixer 21, 22 ... Polarized light beam splitting / mixing surface 31, 32, 33, 34, 35 ... Optical path 41, 42, 43 ... Reciprocating optical path forming means 51, 52, 53, 54, 55, 56, 57, 58, 5
9, 60, 61 ... Quarter-wave plate 71, 72, 73, 74, 75, 76, 77, 78, 7
9 ... Optical path transfer means 81, 82, 83, 84, 85, 86, 91, 92, 9
3, 94, 105, 106 ... Planar reflector 87, 88, 89, 90 ... Retro-reflector 95 ... Beam splitter 96 ... Reflector

Claims (6)

[Claims] 1. A light source for supplying a coherent light flux, a splitting means for splitting the light flux from the light source into two light fluxes, and a pair of first and second pairs arranged to face the splitting means.
A reciprocating optical path forming unit having a reflector for making one reciprocation of one of the light beams divided by the dividing unit; and an interference optical system for interfering the one and the other of the light beams divided by the dividing unit, An interferometer system comprising: a photodetector that detects interfering light beams; and a relative optical path length change of the two light beams is measured from an output of the photodetector. 2. A light beam passing through the reciprocating optical path forming means is arranged so as to be reflected in parallel with and not coincident with the optical axis of the light beam, and the reflected light beam is made to enter the reciprocating optical path forming means again. The interferometer system according to claim 1, further comprising optical path transfer means. 3. The reciprocating optical path forming means is arranged such that the one light beam reciprocates the same number of times as the one light beam reciprocates the first and second reflectors. Further comprising a fourth reflector, the third and fourth
An optical path of the other light flux that travels back and forth through a reflector;
The interferometer system according to claim 1 or 2, wherein the optical path of one of the light fluxes that reciprocates through the second reflector is an optical path that is close to the optical path. 4. The splitting means is a polarization beam splitter, and the optical path forming means further includes quarter-wave plates disposed between the polarization beam splitter and the first and second reflectors, respectively. The interferometer system according to claim 1, 2, or 3. 5. The interferometer system according to claim 1, wherein the interferometer system has a plurality of round-trip optical path forming means. 6. The light flux according to claim 1, wherein the one light beam split by the splitting means makes two or more round trips between the first and second reflectors. Interferometer system.