JP3221507B2 - Interferometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer having a high stability at a high temperature, for example.

[0002]

2. Description of the Related Art A laser interferometer is known as an apparatus capable of measuring a change in relative distance between a first point and a second point with high accuracy. The laser interferometer changes the interference fringes when the difference between the optical path length of the first laser beam reflected from the first point and the optical path length of the second laser beam reflected from the second point changes. Alternatively, a change in the beat signal is converted into a count pulse or the like. For example, by integrating and counting the count pulse, a relative distance between the two can be obtained.

In this case, the optical path length is the product of the actual length of the optical path of the laser beam and the refractive index of the medium through which the beam passes. For example, as disclosed in Japanese Patent Application Laid-Open No. 63-228003, the optical path length generally has a portion caused by many optical paths of a laser beam passing through air having a small refractive index (close to 1) and a refractive index. And a portion of the laser beam that passes through a medium such as glass having a high refractive index due to multiple optical paths. Therefore, when the temperature inside the medium such as glass changes due to a change in the surrounding temperature or a change in the heat of the supporting member, and the refractive index changes, the relative distance between the first point and the second point changes. The difference in optical path length may change even though the distance is not changed, and a change in distance may be erroneously detected by the laser interferometer.

In recent years, laser interferometers have been used for applications requiring extremely high measurement accuracy, such as displacement detectors of projection exposure apparatuses for manufacturing semiconductor devices, and have been subject to measurement errors due to thermal factors. It is desired to eliminate as much as possible. JP-A-63-228003 mentioned above proposes the following interferometer as an interferometer capable of reducing a measurement error due to thermal factors and detecting a change in distance with high accuracy even at a high temperature. I have.

FIG. 3 (a) shows the conventional interferometer. In FIG. 3 (a), reference numeral 1 denotes a laser light source for a two-frequency laser. The first beam having a frequency f1 linearly polarized in a parallel direction and the frequency f linearly polarized in a direction perpendicular to the plane of FIG.
2 (f2 ≠ f1) is emitted in the X direction in a mixed form. Reference numeral 2 denotes a prism body formed by bonding a right-angle prism 3 and a parallelepiped 4 having a parallelogram parallel to the paper surface of FIG. 3A, and the bonding surface of the right-angle prism 3 and the parallel hexahedron 4 is Polarized beam splitter surface 2a
And one surface of a parallelepiped parallel to the surface 2a is a reflection surface 2b. The reflection surface 2b may be a mirror using total reflection. That is, the prism body 2 can be regarded as an optical member in which the polarization beam splitter surface 2a and the reflection surface 2b are arranged in parallel. The polarization beam splitter surface 2a is perpendicular to the paper surface of FIG.
The prism bodies 2 are arranged so as to intersect at 5 °.

[0006] Laser beams (first and second beams) from the laser light source 1 are incident on the polarizing beam splitter surface 2 a of the prism body 2 at an incident angle of 45 °.
The first beam is P-polarized light with respect to the surface 2a, passes through the surface 2a as it is, and passes through the 波長 wavelength plate 5 to the reference mirror 6
And the first beam reflected by the reference mirror 6 is 1 /
The light again enters the polarizing beam splitter surface 2a of the prism body 2 via the four-wavelength plate 5. At this time, the 波長 wavelength plate 5
, The first beam is S-polarized with respect to the surface 2a, so that the first beam is reflected by the surface 2a and travels toward the corner cube 7.

The first light reflected by the corner cube 7
The beam is incident on the polarization beam splitter surface 2 a of the prism body 2 after the polarization plane is rotated by 90 ° by the half-wave plate 8. The position of incidence on the surface 2a is a position shifted from the emission position in a direction parallel to the plane of FIG. 3A. In this case, since the first beam is P-polarized by the half-wave plate 8, the first beam is transmitted through the surface 2a as it is,
After being reflected by b, the light enters the reference mirror 6 via the quarter-wave plate 5. Again, the first beam reflected by the reference mirror 6 passes through the quarter-wave plate 5, is reflected by the reflection surface 2b of the prism body 2, and enters the polarization beam splitter surface 2a. In this case, the first beam is converted into S-polarized light by reciprocating through the quarter-wave plate 5, so that the first beam is reflected by the surface 2a and enters the receiver 10. The receiver 10 contains an analyzer and a light receiving element.

On the other hand, a second beam of the laser beam incident on the polarization beam splitter surface 2a of the prism body 2 from the laser light source 1 is S-polarized with respect to the surface 2a, and this second beam is reflected by the surface 2a. After that, the light is reflected by the reflection surface 2b. Thereafter, the second beam enters the movable mirror 9 via the quarter-wave plate 5. The movable mirror 9 is wider than the reference mirror 6 and is movably held in the X direction in a region shifted in the X direction. The second beam reflected by the movable mirror 9 is 1
After passing through the 波長 wavelength plate, the light is again reflected on the reflection surface 2b of the prism body 2 and enters the polarization beam splitter surface 2a. At this time, since the second beam is P-polarized with respect to the surface 2a by reciprocating through the quarter-wave plate 5, the second beam passes through the surface 2a and travels toward the corner cube 7.

The second light reflected by the corner cube 7
The beam is incident on the polarization beam splitter surface 2 a of the prism body 2 after the polarization plane is rotated by 90 ° by the half-wave plate 8. In this case, since the second beam is converted into S-polarized light by the half-wave plate 8, the second beam is reflected by the surface 2a and then enters the movable mirror 9 via the quarter-wave plate 5. The second beam reflected by the movable mirror 9 again enters the polarization beam splitter surface 2a of the prism 2 via the quarter-wave plate 5. This time, by reciprocating the quarter-wave plate 5,
Since the second beam is P-polarized, it passes through the surface 2a and enters the receiver 10. In the receiver 10, the first beam reflected twice by the reference mirror 6 and the second beam reflected twice by the movable mirror 9 are incident on the light receiving element with their polarization directions aligned by the analyzer.

From the light receiving element of the receiver 10, the movable mirror 9
Is stopped, a beat signal having a frequency of (f1-f2) is output, and when the movable mirror 9 moves, a beat signal whose frequency is modulated is output. Therefore, by integrating the change in the frequency, the amount of movement of the movable mirror 9 in the X direction with respect to the reference mirror 6 can be detected.

FIG. 3B shows the prism 2 of the interferometer of FIG. 3A, and the width of the prism 2 in the X direction is d1.
1. Assuming that the length in the direction orthogonal to the X direction is d12, the following relationship exists. d12 = 2 · d11 Also, if the beam diameter of the laser beam is φ, the width d1
1 needs to be about 2φ or more.

[0012]

The optical path of the first beam and the second beam in the prism body 2 in the interferometer of FIG. 3A will be discussed with reference to FIG. As shown in FIG. 3B, inside the parallelepiped 4 of the prism body 2, the optical paths of the first beam and the second beam are T11 and T21, respectively, except for a common optical path, and the right-angle prism 3
, The optical paths of the first beam and the second beam are T12 and T22, respectively, except for the common optical path. Since T11 + T12 = T21 + T22 holds, the optical path of the first beam and the second
It is equal to the optical path of the beam.

However, when the parallelepiped 4 and the rectangular prism 3 are individually examined, the parallelepiped 4 has a T
11> T21 holds, and T12 <T22 holds for the right-angle prism 3. Therefore, the parallelepiped 4
Even if the refractive indexes of the right-angle prism 3 and the right-angle prism 3 are equal, if the temperatures of the two become different, the optical path difference between the first beam and the second beam changes, and the moving mirror 9 stops. Nevertheless, it is detected that the movement amount has changed. That is, in the configuration of FIG. 3A, there is a disadvantage that a measurement error occurs when a temperature difference occurs between the optical members constituting the prism body 2.

As shown in FIG. 3B, the width of the prism body 2 in the X direction is d11. However, since two laser beams must pass in parallel between the widths d11, the width is d11. There is also an inconvenience that d11 becomes large and the prism body 2 itself is large. Such a large prism body 2 means that the internal temperature difference is likely to be further increased. In view of the above, an object of the present invention is to provide an interferometer having a small measurement error even when a temperature difference occurs between optical members.

[0015]

A first interferometer according to the present invention comprises, as shown in FIG. 1, a light source (1) for supplying a coherent beam, a first polarization splitting surface (11a) and a first reflection. Planes (11b) are provided orthogonal to each other, and the first polarization separation plane separates the beam from the light source into a first beam in a first direction (X direction) and a second beam in a second direction. A second polarization splitter parallel to the first polarization splitter and parallel to the ridge formed by the first optical member (the lower half of 11), the first polarization splitter and the first reflective surface; A second optical member (an upper half of 11) in which a surface (11a) and a second reflection surface (11b) parallel to the first reflection surface are provided orthogonal to each other; A first quarter provided parallel to a first reference plane inclined at 45 ° to one reflection surface Long plate (14a) and second quarter
A wavelength plate (14b) and a third quarter provided parallel to the first reference plane and parallel to a second reference plane inclined at 45 ° to the second polarization separation plane and the second reflection plane. And a fourth quarter-wave plate (14d), and the first beam separated in the first direction by the first polarization splitting surface into the first quarter. The light is reflected through the wave plate and returned to the first polarization splitting surface again.
A first reflecting member (15) for reflecting the first beam returned to the polarization splitting surface through the first reflecting surface and the second quarter-wave plate and returning the first beam to the first polarization splitting surface; This first
The first beam guided in the second direction by being returned to the first polarization splitting surface by the two reflections of the reflecting member and the light source split in the second direction at the first polarization splitting surface A deflecting optical member (17) for deflecting each of the second beams of the first and second beams to the second polarization splitting surface, and for deflecting the first beam in the first direction at the second polarization splitting surface; Respectively in the second direction, until the first beam and the second beam 2 emitted from the first polarization separation surface in the second direction reach the second polarization separation surface by the deflection optical member. And a polarization plane rotating means (18) for rotating the polarization planes of the first beam and the second beam by 90 degrees, respectively, and the second beam guided in the second direction by the second polarization splitting plane. 2 reflective surface and its third 4 And returns to the second polarization splitting surface again, and reflects the second beam returned to the second polarization splitting surface via the fourth quarter wave plate. A second reflection member (16) returning to the second polarization splitting surface, and returning to the second polarization splitting surface by two reflections of the second reflection member, thereby causing the second polarization splitting surface to return to the second polarization splitting surface. Light receiving means (10) for receiving the first beam guided in two directions and the second beam guided in the second direction at the second polarization splitting surface, the first reflecting member (15 ) And the relative movement amount of the second reflection member (16).

The second interferometer according to the present invention comprises a light source (1) for supplying a coherent beam, a first polarization splitting surface (11a) and a first reflecting surface (11b) as shown in FIG. ) Are provided orthogonal to each other, and a first optical member that separates a beam from the light source into a first beam in a first direction (X direction) and a second beam in a second direction by the first polarization separation surface. (Lower half of 11), and a second polarization separation surface (11a) which is arranged in parallel in a ridge direction formed by the first polarization separation surface and the first reflection surface, and is parallel to the first polarization separation surface. ) And a second reflecting surface (11) parallel to the first reflecting surface.
b) are provided perpendicular to each other.
Upper half), and a first reference plane provided in parallel with a first reference plane inclined by 45 ° with respect to the first polarization separation plane and the first reflection plane.
And a second quarter-wave plate (14a) and a second quarter-wave plate (14b), which are parallel to the first reference plane and 45 degrees with respect to the second polarization separation plane and the second reflection plane. ３A third quarter-wave plate (14) provided in parallel with the tilted second reference plane.
c) and the fourth quarter wavelength (14d) and the first beam separated in the first direction by the first polarization splitting surface is reflected through the first quarter wave plate. To return to the first polarization splitting surface, and reflect the first beam returned to the first polarization splitting surface through the first reflecting surface and the second quarter-wave plate. A first reflecting member returning to the first polarization separating surface, and the first beam guided in the second direction by being returned to the first polarizing separating surface by two reflections of the first reflecting member; A first deflecting optical member (17) for deflecting the second beam from the light source, which is split in the second direction at the first polarization splitting surface, and leading the second beam to the second polarization splitting surface; The first beam is directed to the first direction at the two-polarized light separating surface, and the second beam is directed to the second direction. To divide each direction, the first emitted from the first polarization separating surface thereof in its second direction 1
Polarization plane rotating means (18A) for rotating the polarization planes of the first beam and the second beam by 90 degrees before the beam and the second beam reach the second polarization splitting plane by the first deflection optical member; The second beam guided in the second direction by the second polarization splitting surface is reflected through the second reflecting surface and the third quarter-wave plate, and the second polarization splitting surface is returned again. A second reflecting member (16) for reflecting the second beam returned to the second polarization splitting surface through the fourth quarter-wave plate and returning the second beam to the second polarization splitting surface. The first beam guided in the second direction at the second polarization splitting surface by being returned to the second polarization splitting surface by the two reflections of the second reflecting member and the second polarization splitting surface. When guided in the second direction, the second beam is Its second toward the polarization separation surface is deflected, respectively shifting the second deflection optical member in the reverse optical path and parallel to the parallel optical path of the first and second beams are traced respectively (23)
Receiving light receiving the first and second beams emitted from the first polarization splitting surface by tracing parallel optical paths parallel to the opposite optical paths followed by the first and second beams by the second deflecting optical member; Means (10), and the first reflecting member (1
5) and a relative movement amount between the second reflection member (16) and the second reflection member (16).

In the first and second interferometers, the first optical member (the lower half of 11) and the second optical member (the upper half of 11) may be integrally formed. .

[0018]

According to the first interferometer of the present invention, the first reflecting member (15) and the second reflecting member (16) are in the first direction (X direction) which is the traveling direction of the first beam. Can be displaced in the direction perpendicular to. Then, the first beam reflected twice by the first reflecting member (15) and the second beam reflected twice by the second reflecting member (16) are mixed and received by the light receiving means (10). Therefore, when the relative position of the first reflecting member (15) and the second reflecting member (16) in the X direction changes, the optical path length of the first beam and the second beam changes, and interference in the light receiving means (10) occurs. Since the fringe or beat signal changes, the relative movement amount of both members (15, 16) can be detected.

In this case, the first optical member and the second optical member are, for example, as shown in FIG.
a) and the reflection surface (11b) are arranged orthogonally.
When the width of the first optical member and the second optical member in the X direction is d1, the length d2 of these members in the direction perpendicular to the X direction has a relationship of d2 = 2 · d1. Further, in the present invention, since it is sufficient that one beam can pass between the widths d1, the width d1 can be set to about 1/2 of the width d11 of the conventional prism body 2 in FIG. 3B. Accordingly, the total volume of the first optical member and the second optical member is about 1/2 of the volume of the conventional prism body 2, and the internal temperature difference is reduced, so that the measurement error caused by the temperature difference is reduced.

In particular, when the first optical member and the second optical member are integrated into an optical member (11), the first beam and the second beam have the same length above and below the optical member (11). It passes through the optical path. Therefore, even if the temperature of the optical member (11) changes, the optical path difference between the two does not change, and measurement can be performed with higher accuracy.

According to the second interferometer of the present invention, the first beam reflected twice by the first reflecting member (15) is the second beam.
After being reflected by the deflection optical member (23), the first
The light is reflected twice by the reflecting member (15) and enters the light receiving means (10). Similarly, the second beam reflected twice by the second reflecting member (16) is also reflected by the second deflecting optical member (23) and then again reflected twice by the second reflecting member (16) to receive light. (10). Therefore, the light receiving means (1
0), the first reflection member (15) reflected four times by the first reflection member (15).
Since the beam and the second beam reflected four times by the second reflection member (16) are mixed and received, the detection resolution of the relative movement amount is doubled compared to the first interferometer. You.

Even in this case, when the first optical member and the second optical member are integrated into an optical member (11), the optical path difference between the two changes even if the temperature of the optical member (11) changes. Measurement can be performed with higher accuracy.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of an interferometer according to the present invention will be described below with reference to FIG. The laser light source 1 and the receiver 10 of this embodiment are the same as those used in the conventional example shown in FIG. FIG. 1A shows a main part of the laser interferometer of the present embodiment. In FIG. 1A, reference numeral 11 denotes a prism body formed by bonding a first rectangular prism 12 and a second rectangular prism 13 together. is there. This prism body 1
1 is, as shown in FIG.
The length of the hypotenuse and the length of the hypotenuse of the right-angle prism 12 are d2 (= 2
(D1) The right side prism 13 is bonded to one of two orthogonal sides thereof. The bonding surface is defined as a polarization beam splitter surface 11a, and the other of the two orthogonal sides of the right-angle prism 13 is defined as a reflection surface 11b. The reflection surface 11b may use total reflection.

Accordingly, the prism body 11 may be any as long as the polarizing beam splitter surface 11a and the reflecting surface 11b are arranged orthogonally. For example, as shown in FIG. 1C, a prism body 19 is formed by bonding three right-angle prisms 20 to 22 and a bonding surface between the right-angle prisms 20 and 21 is defined as a polarization beam splitter surface 19a. If the outer surface of the prism 22 is the reflection surface 19b, the prism body 19 can be used instead of the prism body 11.

Returning to FIG. 1A, the direction in which two laser beams (first beam and second beam) having different frequencies are emitted from the laser light source 1 is defined as the X direction, and the polarization beam splitter surface of the prism body 11 is defined as the X direction. 11a is 4 in the X direction
The prism bodies 11 are arranged so as to intersect at 5 °. Further, a quarter-wave plate 14 is arranged in the X direction, and then a first movable mirror 15 and a second movable mirror 16 each of which is a plane mirror are arranged so as to be movable in the X direction. These movable mirrors 15
And 16 are displaced in a direction perpendicular to the X direction.

Further, a right-angle prism 17 is arranged in a direction in which the laser beam from the laser light source 1 is reflected in a region P11 of the polarization beam splitter surface 11a of the prism body 11. In this case, assuming that the laser beam is returned to the region P13 of the polarization beam splitter surface 11a by the two total reflections in the right-angle prism 17, the polarization beam splitter surface 11a and the reflection surface 11b of the prism body 11 are assumed.
The right-angle prism 17 is positioned so that the region P11 and the region P13 are positioned on a straight line parallel to the ridge line. Further, a half-wave plate 18 is arranged in the middle of one optical path between the prism body 11 and the right-angle prism 17. However, instead of the half-wave plate 18, a quarter-wave plate 17 is formed so as to cover the entire entrance and exit surfaces of the rectangular prism 17.
A wave plate may be provided. Further, the receiver 10 is arranged in the direction in which the laser beam from the right-angle prism 17 is reflected in the region P13 of the polarization beam splitter surface 11a.

Next, the operation of this embodiment will be described. First,
The laser beams (first and second beams) from the laser light source 1 are incident on the region P11 of the polarizing beam splitter surface 11a of the prism body 11 at an incident angle of 45 °.
The first beam of P-polarized light passes through the surface 11a as it is with respect to the surface 11a, and passes through the quarter-wave plate 14 to the first beam.
The first beam reflected by the movable mirror 15 is again incident on the polarization beam splitter surface 11a of the prism body 11 via the quarter-wave plate 14. At this time, since the first beam is S-polarized with respect to the surface 11a due to the reciprocating movement of the quarter-wave plate 14, the first beam is reflected by the region P11 of the surface 11a and is reflected by the region of the reflection surface 11b. Head to P12.

The first beam reflected by the reflecting surface 11b passes through the quarter-wave plate 14 to the area P of the first movable mirror 15
The second beam which is incident on the reflection region 22 and reflected by the region P22 is a quarter-wave plate 14 and the reflection surface 11b of the prism body 11.
And enters the region P11 of the polarization beam splitter surface 11a through the region P12. In this case, since the first beam is P-polarized, the polarization beam splitter surface 1 is left as it is.
The light passes through 1a and goes to the right-angle prism 17.

The first beam reflected by the right-angle prism 17 is incident on the region P13 of the polarization beam splitter surface 11a of the prism body 11 after the polarization plane is rotated by 90 ° by the half-wave plate 18. In this case, since the first beam is S-polarized by the half-wave plate 18, the first beam is reflected by the region P13 of the surface 11a and enters the receiver 10.

On the other hand, from the laser light source 1 to the prism 11
Of the laser beam incident on the region P11 of the polarization beam splitter surface 11a of the
The beam is reflected by the area P11 on the surface 11a and travels to the right-angle prism 17. The second beam reflected by the right-angle prism 17 passes through the half-wave plate 18 to the prism 1
The light enters the region P13 of the first polarization beam splitter surface 11a. Since the second beam is P-polarized by the half-wave plate 18, the second beam is transmitted through the region P13 of the surface 11a as it is, and then reflected by the region P14 of the reflection surface 11b. Thereafter, the second beam enters the region P31 of the second movable mirror 16 via the quarter-wave plate 14.

The second beam reflected by the region P31 of the second movable mirror 16 passes through the quarter-wave plate 14, is reflected again by the region P14 of the reflecting surface 11b of the prism 11, and is reflected by the polarizing beam splitter surface 11a. The light enters the region P13.
At this time, by reciprocating the quarter-wave plate 14, the second
Since the beam is S-polarized with respect to the surface 11a, the second beam is reflected by the region P13 of the surface 11a. After that, the second beam enters the region P32 of the second movable mirror 16 via the quarter-wave plate 14, and the second beam reflected on this region P32 passes through the quarter-wave plate 14 to form a prism. The process returns to the region P13 of the eleventh polarization beam splitter surface 11a. This time, by reciprocating the quarter wave plate 14,
Since the second beam is P-polarized light, it passes through the region P13 of the surface 11a and enters the receiver 10. In the receiver 10, the first beam reflected twice by the first movable mirror 15 and the second beam reflected twice by the second movable mirror 16 have their polarization directions aligned by the analyzer and are incident on the light receiving element. I do.

When the first movable mirror 15 and the second movable mirror 16 are relatively stopped in the X direction from the light receiving element of the receiver 10, a beat signal having a frequency of (f1-f2) is generated. When both are relatively moved in the X direction, a beat signal whose frequency is modulated is output. Therefore, by integrating the change in the frequency, the first movable mirror 15
And the second moving mirror 16 in the X direction can be detected.

In this case, in this example, as is clear from FIG. 1A, the first beam and the second beam pass through the same optical path inside the right angle prism 12 of the prism body 11. Further, inside the right angle prism 13 of the prism body 11, the first beam and the second beam pass through an optical path of the same length vertically separated from each other (that is, an optical path T shown in FIG. 1B). Therefore, even if a temperature difference occurs between the right-angle prism 12 and the right-angle prism 12, the difference in the optical path length between the first beam and the second beam does not change. Further, assuming that the beam diameters of the first beam and the second beam are φ, the width d1 of the prism body 11 of the present example may be about φ in FIG.

On the other hand, the width d11 of the conventional prism 2 shown in FIG. 3 (a) needs to be about 2φ, and the optical paths of both beams inside the prism 11 of this embodiment are the same as those of the conventional prism 2. Since the optical paths of the two internal beams are about half, the difference in the optical path length due to the internal temperature variation is small. Therefore, highly accurate displacement detection can always be performed. The volume of the prism 11 is 1 / the volume of the prism 2.
This is about two, and according to this example, the entire interferometer can be further downsized.

In the embodiment of FIG. 1A, a case has been described in which one quarter wavelength plate 14 is formed. However, each region P21, P22 of the first movable mirror 15 and the second movable mirror 14 are formed. 4 which reciprocates by reflection of each area P31, P32 of the mirror 16
1/4 wavelength plates 14a to 14d
Needless to say, 14d may be arranged. Further, in the embodiment shown in FIG.
The laser light source 1 and the receiver 10 are arranged on a first surface side of a right-angle prism 12 having two surfaces, and 1 /
A two-wave plate 18 and a right-angle prism 17 are arranged.
However, the laser light source 1 and the receiver 10 may be arranged on the second surface side, and the half-wave plate 18 and the right-angle prism 17 may be arranged on the first surface side. The position with the receiver 10 may be exchanged.

Next, another embodiment of the present invention will be described with reference to FIG. In this embodiment, the resolution of the embodiment shown in FIG. 1 is further increased. In FIG. 2, portions corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 2 shows a configuration of a main part of the laser interferometer of the present embodiment.
23 is a right angle prism. With this right angle prism 23,
The first beam and the second beam emitted from the region P13 of the polarization beam splitter surface 11a of the prism body 11 are reflected and incident on the region P15 of the polarization beam splitter surface 11a. The region P15 is located at a position parallel to the ridge line between the polarization beam splitter surface 11a and the reflection surface 11b with respect to the region P13. The circular half-wave plate 18 shown in FIG.
Is replaced with a rectangular half-wave plate 18A.

Further, assuming that a position from the region P15 of the polarization beam splitter surface 11a to the right-angle prism 17 and a position where the laser beam reflected by the right-angle prism 17 is incident on the polarization beam splitter surface 11a is a region P16, this region P16 The receiver 10 is arranged in the reflected direction.

The operation of this embodiment will be described. First, the operation of the optical path from the laser light source 1 to the region P13 of the polarizing beam splitter surface 11a of the prism body 11 is the same as that in the example of FIG. Then, the first beam traveling from the region P13 of the polarization beam splitter surface 11a to the right-angle prism 23 is reflected by the right-angle prism 23 and enters the region P15 of the polarization beam splitter surface 11a. The first beam is S
Since the light is polarized, the polarization beam splitter surface 11a
At the right-angle prism 17 via the half-wave plate 18A. The first light reflected by the right-angle prism 17
The beam is the polarized beam splitter surface 1 of the prism body 11.
The light enters the region P16 of 1a. The first beam converted into P-polarized light by the half-wave plate 18A passes through the region P16 of the surface 11a as it is, and then enters the region P17 of the reflection surface 11b. After being reflected by this region P17, the first beam becomes 1
4 and enters the region P23 of the first movable mirror 15.

The first mirror 15 reflected from the first movable mirror 15
The beam is applied to the region P1 of the quarter-wave plate 14 and the reflection surface 11b.
7, the region P16 of the polarization beam splitter surface 11a
And is reflected by this surface 11a. Thereafter, the first beam enters the region P24 of the first movable mirror 15 via the quarter wavelength plate 14, and the first beam reflected by the first movable mirror 15 passes through the quarter wavelength plate 14. To return to the region P16 of the polarization beam splitter surface 11a. Since the first beam is P-polarized light, it passes through the surface 11a and enters the receiver 10 as it is.

On the other hand, the second beam from the region P13 on the polarization beam splitter surface 11a toward the right-angle prism 23 is reflected by the right-angle prism 23 and enters the region P15 on the polarization beam splitter surface 11a. The first beam is P
Since the light is polarized, the polarization beam splitter surface 11a
Through the 波長 wavelength plate 14 and the second movable mirror 16
In the region P33. The second beam reflected by the second movable mirror 16 is incident on the region P15 of the polarization beam splitter surface 11a via the quarter-wave plate 14, and is reflected by this surface 11a. After that, the second beam is applied to the reflecting surface 11.
After being reflected by the region P18 of b, the light enters the region P34 of the second movable mirror 16 via the quarter-wave plate 14, and the second beam reflected by this region P34 is reflected by the quarter-wave plate 14 and the reflection plate. The light enters the region P15 of the polarization beam splitter surface 11a via the region P18 of the surface 11b.

In this case, since the second beam is P-polarized light, it passes through the region P15 as it is, and
Then, the second beam reflected by the right-angle prism 17 is incident on a region P16 of the polarization beam splitter surface 11a of the prism body 11. Since the second beam is S-polarized by the half-wave plate 18A, the second beam is reflected by the region P16 of the surface 11a and enters the receiver 10. The receiver 10 has the first movable mirror 1
The first beam reflected four times at 5 and the fourth beam at the second moving mirror 16
The second reflected beam is mixed and incident. Accordingly, in the example shown in FIG. 1, for example, N is set for a predetermined relative movement amount in the X direction between the first movable mirror 15 and the second movable mirror 16.
Assuming that a count pulse for counting is obtained, a count pulse twice as large as 2N counts is obtained in the example of FIG. Therefore,
In the example of FIG. 2, the resolution is doubled.

Also in the example of FIG. 2, the lengths of the optical paths inside the right-angle prisms 12 and 13 constituting the prism body 11 of the first beam and the second beam are equal. Therefore, even if a temperature difference between the right-angle prism 12 and the right-angle prism 13 occurs, the difference in the optical path length between the two beams does not change.
No measurement error occurs. In FIG. 2, the receiver 1
By disposing another right-angle prism or corner cube at the position where 0 is disposed and shifting the position of the receiver 10, the resolution can be further improved.

Further, in the embodiment shown in FIG.
4 is constituted by one sheet, but as shown by the dotted line, the quarter wavelength plate 14a is disposed in two reciprocating optical paths which reciprocate by reflection of the respective regions P21 and P24 of the first movable mirror 15.
The 往復 wavelength plate 14b and the second quarter-wave plate 14b
In the two reciprocating optical paths reciprocating by the reflections of the respective areas P31 and P34 of the movable mirror 16, the quarter wavelength plate 14c and the two reciprocating optical paths reciprocating by the reflections of the respective areas P32 and P33 of the second movable mirror 16 Needless to say, the 1/4 wavelength plate 14d may be divided and arranged.

Although the above embodiment is an example in which the present invention is applied to a heterodyne type laser interferometer, the present invention can be similarly applied to a homodyne type interferometer. Further, a corner cube or the like may be used instead of the right-angle prisms 17 and 23. As described above, the present invention is not limited to the above-described embodiment, and can take various configurations without departing from the gist of the present invention.

[0045]

According to the first interferometer of the present invention, there is an advantage that a measurement error is small even if a temperature difference occurs between the optical members constituting the first optical member and the second optical member. Further, the combined volume of the first optical member and the second optical member is smaller than the volume of the conventional prism body, and the interferometer can be downsized as a whole.

According to the second interferometer, since the second deflecting optical member is provided, there is an advantage that the resolution is further doubled. Further, when the first optical member and the second optical member are integrated, there is an advantage that a measurement error is small even if a temperature difference occurs between the optical members.

[Brief description of the drawings]

FIG. 1A is a perspective view showing one embodiment of an interferometer according to the present invention, FIG. 1B is a plan view of a prism body 11 of the embodiment,
(C) is a plan view showing another example of the prism body of the embodiment.

FIG. 2 is a perspective view showing another embodiment of the present invention.

3A is a configuration diagram showing a conventional interferometer, and FIG. 3B is a plan view of a conventional prism body 2. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 10 Receiver 11 Prism body 12, 13 Right angle prism 14 1/4 wavelength plate 15 1st moving mirror 16 2nd moving mirror 17 Right angle prism 18, 18A 1/2 wavelength plate 23 Right angle prism

Claims (3)

(57) [Claims] 1. A light source for supplying a coherent beam, a first polarization separation surface and a first reflection surface are provided orthogonal to each other, and a beam from the light source in a first direction is provided by the first polarization separation surface. A first optical member for separating a first beam and a second beam in a second direction, the first optical member being arranged side by side in a ridgeline direction formed by the first polarization separation surface and the first reflection surface; A second optical member in which a second polarization separation surface parallel to the polarization separation surface and a second reflection surface parallel to the first reflection surface are provided orthogonal to each other; the first polarization separation surface and the first reflection A first and a second quarter-wave plate provided in parallel with a first reference plane inclined at 45 ° with respect to a plane; a second polarization separation plane parallel to the first reference plane and the second polarization separation plane; Third and fourth quarter waves provided in parallel with a second reference plane inclined at 45 ° with respect to the two reflection planes A plate, and the first beam separated in the first direction by the first polarization separation surface is reflected via the first quarter-wave plate and returned to the first polarization separation surface again. A first reflection member that reflects the first beam returned to the first polarization separation surface through the first reflection surface and the second quarter-wave plate and returns the first beam to the first polarization separation surface; The first beam guided in the second direction by being returned to the first polarization splitting surface by two reflections of the first reflection member and split in the second direction by the first polarization splitting surface. A deflecting optical member for deflecting the second beam from the light source and guiding the second beam to the second polarization splitting surface; and the second beam splitting the first beam in the first direction at the second polarization splitting surface. To separate in the second direction, respectively, from the first polarization splitting surface. The polarization planes of the first beam and the second beam are rotated by 90 degrees before the first beam and the second beam 2 emitted in the second direction reach the second polarization splitting plane by the deflection optical member. Polarization plane rotating means; and the second beam guided in the second direction by the second polarization splitting plane. The second reflection plane and the third quarter.
The light reflected through the wave plate and returned to the second polarization separation surface again, and the second beam returned to the second polarization separation surface is reflected through the fourth quarter-wave plate and reflected. A second reflection member returning to the second polarization separation surface; and being returned to the second polarization separation surface by two reflections of the second reflection member, guided by the second polarization separation surface in the second direction. Light receiving means for receiving the first beam and the second beam guided in the second direction by the second polarization splitting surface; and a relative position between the first reflection member and the second reflection member. An interferometer characterized by detecting a large amount of movement. 2. A light source for supplying a coherent beam, a first polarization separation surface and a first reflection surface are provided orthogonal to each other, and a beam from the light source in a first direction is provided by the first polarization separation surface. A first optical member for separating a first beam and a second beam in a second direction, the first optical member being arranged side by side in a ridgeline direction formed by the first polarization separation surface and the first reflection surface; A second optical member in which a second polarization separation surface parallel to the polarization separation surface and a second reflection surface parallel to the first reflection surface are provided orthogonal to each other; the first polarization separation surface and the first reflection A first and a second quarter-wave plate provided in parallel with a first reference plane inclined at 45 ° with respect to a plane; a second polarization separation plane parallel to the first reference plane and the second polarization separation plane; Third and fourth quarter waves provided in parallel with a second reference plane inclined at 45 ° with respect to the two reflection planes A plate, and the first beam separated in the first direction by the first polarization separation surface is reflected via the first quarter-wave plate and returned to the first polarization separation surface again. A first reflection member that reflects the first beam returned to the first polarization separation surface through the first reflection surface and the second quarter-wave plate and returns the first beam to the first polarization separation surface; The first beam guided in the second direction by being returned to the first polarization splitting surface by two reflections of the first reflection member and split in the second direction by the first polarization splitting surface. A first deflecting optical member that deflects the second beam from the light source and guides the second beam to the second polarization splitting surface, and the first beam in the first direction at the second polarization splitting surface. The first polarization splitting surface for splitting the two beams in the second direction, respectively; The polarization planes of the first beam and the second beam are respectively adjusted by 90 before the first beam and the second beam emitted from the first direction and the second beam reach the second polarization separation plane by the first deflection optical member. Polarization plane rotating means for rotating the second beam by a second degree, and the second beam guided in the second direction by the second polarization splitting surface. The second reflection surface and the third quarter.
The light reflected through the wave plate and returned to the second polarization separation surface again, and the second beam returned to the second polarization separation surface is reflected through the fourth quarter-wave plate and reflected. A second reflection member returning to the second polarization separation surface; and being returned to the second polarization separation surface by two reflections of the second reflection member, guided by the second polarization separation surface in the second direction. When guided in the second direction by the first beam and the second polarization splitting surface, the second beam is deflected again toward the second polarization splitting surface, and the first and second beams follow respectively. A second deflecting optical member which is respectively shifted to a parallel optical path parallel to the reverse optical path; and the first deflecting optical member traces a parallel optical path parallel to the reverse optical path followed by the first and second beams by the second deflecting optical member. Light receiving means for receiving the first and second beams emitted from the polarization splitting surface Has the door, interferometer, characterized in that for detecting the amount of relative movement between said second reflecting member and the first reflecting member. 3. The interferometer according to claim 1, wherein the first optical member and the second optical member are provided integrally.