JPH01307605A - Plane mirror interference optical system - Google Patents

Abstract

PURPOSE:To reduce the influence caused by a thermal expansion of an optical element by forming a reflecting surface in parallel to a polarization film in a corner part of a polarization beam splitter. CONSTITUTION:In the lower part of a polarization beam splitter 30, the lower corner cube 34 is placed through a 1/4 wavelength plate 32, and also, in the upper part of the splitter 30, the upper corner cube 36 is placed. The corner cubes 30, 36 are placed in the direction being orthogonal to the incident direction of a laser beam. A polarization film 38 is placed in a state that it has been inclined against the incident direction of a laser beam, and also, a reflecting surface 40 is formed in parallel to the polarization film 38. Also, a 1/4 wavelength plate 42, a reference plane mirror 44 and a moving plane mirror 46 are placed on the side opposite to the incident side of the laser beam by placing the splitter 30 between. In such a way, an optical path of a P polarization measuring light bean and an optical path of an S polarization reference light beam take an extremely adjacent optical path, and these light beams pass through the same optical element by the same number of times, therefore, the influence by a thermal expansion of the optical element can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plane mirror interference optical system, and particularly to a plane mirror interference optical system used in a laser interferometer.

[Conventional technology]

A conventional plane mirror interference optical system is shown in FIG. This interference optical system is composed of a polarizing beam splitter 10, a corner cube 12, a corner cube 14 (reference surface), a quarter wavelength plate 16, a movable plane mirror (measurement surface) 18, and a polarizer 20.

When the laser beam having P-polarized light and S-polarized light enters the polarizing beam splitter 10, the P-polarized measuring light that has passed through the polarizing film 22 passes through the polarizing beam splitter lO as shown by the solid line, and then passes through the quarter-wave plate 16. Passing and further moving plane mirror 1
After being reflected by 8, it passes through optical wave plate l6 and the plane of polarization becomes 9.
It is rotated by 0° and becomes S-polarized light, which is sent to beam splitter 1 again.
0. S incident on the polarizing beam splitter 10
The polarized light is reflected by the polarizing film 22 and passes through the corner cube 12.
After that, the light beam enters the polarizing beam splitter 10 again. Since the light incident on the polarizing beam splitter 10 is S-polarized, it is reflected by the polarizing film 22, passes through the χ wavelength plate 16, is reflected by the movable plane mirror 18, and passes through the X2I12 long plate again, where it is polarized into P-polarized light and becomes a beam. The light passes through the polarizing film 22 of the splitter 10, passes through the polarizer 20, and reaches a receiver (not shown).

On the other hand, the S-polarized reference beam of the laser beam incident on the polarizing beam splitter 10 is reflected by the polarizing film 22 as shown by the dotted line, and is incident on the corner winding 14. corner cube 1
4 is emitted, it is reflected again by the polarizing film 22, emitted from the beam splitter 10, passes through the polarizer 20, and is transmitted to the receiver.
, where the reference target interferes with the measurement light to generate interference fringes.

[Problem that the invention seeks to solve]

However, in the conventional brane mirror interference optical system, although the error occurs little with respect to the inclination of the movable plane mirror 18, as shown by the solid line and dotted line in FIG.
Since the optical path lengths of the optical path (solid line) and the reference optical path (dotted line) are significantly different, there is a drawback that the put-bus is very large and is easily affected by disturbances. Further, as shown in FIG. 5, the measurement optical path and the reference optical path have few common optical paths and pass through the optical paths of different optical elements, which has the disadvantage that large errors occur when each optical element thermally expands.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to propose a brain-mirror interference optical system that has few putbuses and does not generate large errors due to thermal expansion of optical elements.

[Means for solving problems]

In order to achieve the above object, the present invention provides a polarizing beam splitter into which laser light having P-polarized light and S-polarized light is incident, and which has a polarized light film arranged obliquely with respect to the laser light incident direction; a first corner cube disposed on one side of the polarizing beam subrifter in a direction orthogonal to the laser beam incident on the beam subrifter; and a first corner cube disposed between the polarizing beam subrifter and the first corner cube. 1st 1
/4 wavelength plate and a second corner cube disposed on the opposite side of the polarizing beam splitter from the first corner cube in a direction orthogonal to the laser light incident on the polarizing beam splitter, and a second corner cube disposed on the opposite side of the polarizing beam splitter from the first corner cube. a polarizing beam subrifter sandwiched between a second quarter-wave plate, a reference plane mirror, a movable plane mirror disposed on the side opposite to the laser beam incidence side, a second corner cube, and a second two-wavelength plate; It is characterized by consisting of a reflective surface formed parallel to the polarizing film at the corner of the polarizing film.

[Effect]

In the present invention, a reflective surface is formed parallel to the polarizing film at the corner of the polarizing beam splitter sandwiched between the second corner cube and the second quarter-wave plate, so that the measurement light and the reference light are By passing through the same optical element the same number of times, the put-bus is small, and the influence of thermal expansion of the optical element can be reduced.

In addition, in the present invention, since the reference light and the measurement light pass through the same path, they are affected by air fluctuations in the same way.
Errors are reduced.

〔Example〕

Preferred embodiments of the plane mirror interference optical system according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows an optical system showing the optical path of the measurement light of the plane mirror interference optical system according to the present invention, and FIG. 2 shows the optical path of the reference light of the interference optical system according to the invention. Although the above optical paths are formed by the same optical system, for convenience, the optical paths of the measurement light and the reference light will be explained separately. In Figure 1,
A quarter wavelength plate 32 is located below the polarizing beam splitter 30.
A lower corner cube 34 is disposed through the
An upper corner cube 36 is arranged above the polarizing beam splitter 30. corner cube 30.36
is arranged in a direction perpendicular to the direction of incidence of the laser. The polarizing film 38 is arranged obliquely with respect to the direction of incidence of the laser beam, and furthermore, as shown in FIG. 3, a reflective surface is formed parallel to the polarizing film 38. The reflective surface 40 is formed of a metal vapor-deposited surface such as AI or Cr.

On the right side of the polarizing beam subrifter 30 in FIG.
A 4-wavelength plate 42 is arranged, and a reference plane mirror 4 is further placed on the side thereof.
4. A movable plane mirror 46 is arranged.

The reference plane mirror 44 is formed smaller than the movable plane mirror 46 so that the measurement light is not blocked by the reference plane mirror.

The operation of the embodiment according to the present invention constructed as described above is as follows. First, the optical path of the measurement light of the interference optical system of the present invention will be explained with reference to FIG. When the laser light including P-polarized light and S-polarized light enters the polarizing beam splitter 30, the P-polarized light passes through the polarizing film 38 of the polarized beam splitter 30, but the S-polarized light is reflected. The P-polarized light that has passed through the polarization beam splitter 30 passes through a wavelength plate 42 and is then moved to a movable plane mirror 4.
After being reflected by the light beam 6, when it passes through the mirror plate 42 again, the plane of polarization is rotated by 90 degrees and becomes S-polarized light. , Therefore, the polarizing film 3
It is reflected at 8 and changes direction by 90°. This S-polarized light is reflected by the reflective surface 40, then reflected again by the polarizing film 38, and enters the corner cube 36. The direction of the light is changed by 180 degrees by the corner cube 36, and the light emitted from the corner cube 36 is reflected by a reflecting surface 40, passes through a wavelength plate 42, and is reflected by a movable plane mirror 46. The light reflected by the movable plane mirror 46 passes through the wavelength plate 42, and at this time, the plane of polarization is 90°.
The S-polarized light becomes P-polarized light. Thereafter, the light is reflected by the reflective surface 40 and exits from the corner cube 36. Since this light is P-polarized, it passes through the polarizing film 38 and exits the polarizing beam splitter 30. After being emitted from the polarizing beam splitter 30, it passes through a quarter-wave plate 32, passes through a lower corner cube 34, and passes through the wavelength plate 32 again to become S-polarized light.Since it is S-polarized light, it is reflected by a polarizing film 38, and sent to a receiver (not shown). − is reached.

Next, the reference optical path of the interference optical system of the present invention will be explained with reference to FIG. First, the S-polarized light of the laser light incident on the polarizing beam splitter 30 is reflected by the polarizing film 38, passes through the wavelength plate 32, and enters the lower corner cube 34. The S-polarized light emitted from the lower corner cube 34 passes through the V4 long plate, the plane of polarization is rotated by 90 degrees, becomes P-polarized light, and enters the polarizing beam splitter 30 again. Since this light is P-polarized light, it passes through the polarizing film 38, exits the polarizing beam splitter 30, and enters the corner cube 36. The light incident on the corner cube 36 is output with its direction changed by 180 degrees, reflected by the reflective surface 40, passes through the quarter wavelength plate 42, and reaches the reference plane mirror 44. The light reflected by the reference plane mirror 44 passes through the 1/4 wavelength plate 42
At this time, the polarization plane of the P-polarized light is rotated by 90 degrees, and the light is changed into S-polarized light.The direction of the P-polarized light is changed by 90 degrees by the reflecting surface 40, and then the light enters the corner cube 36 again. The light incident on the corner cube 36 becomes a polarized beam again.
The light enters the ivy 30, but because it is S-polarized, the polarizing film 38
The light is reflected by the reflection surface 40, the direction of which is changed by 90', and the light is reflected toward the polarizing film 38. It is reflected by the polarizing film 38 as S-polarized light, exits the polarizing beam splitter 30, passes through the gas-liquid long plate 42, is reflected by the reference plane mirror 44, and then passes through the wavelength plate again to become P-polarized light, which is then sent to the polarizing beam splitter. 30. Since the light incident on the polarizing beam splitter 30 is P-polarized light, it passes through the polarizing film 38 and reaches a receiver (not shown). Here, the measurement light and the reference light interfere to form interference fringes.

According to the embodiment, as shown in FIGS. 1 and 2, the optical path of the measurement light and the reference light are very close, and the optical path of the measurement light and the reference light are very close to each other, and the optical path of the measurement light and the reference light are very close to each other. Not affected by thermal expansion.

In addition, since the measurement light and the reference light are spatially transmitted along almost the same optical path, they should be arranged so that the movable plane mirror 46 and the reference plane mirror 44 are brought as close as possible to minimize the dead bus. I can do it.

Furthermore, although FIG. 4 shows the optical path of the measurement light when the movable plane mirror 46 is tilted, the laser beam returns parallel to the tilted light due to the tilt θ of the plane mirror 46.
The outgoing light is less affected by the tilt of the movable plane mirror 46 than the incident light. Although the optical path of the measurement light has been described in FIG. 4, the optical path of the reference destination is similarly less affected by the inclination of the reference plane mirror 44.

〔Effect of the invention〕

As explained above, according to the brain-mirror interference optical system according to the present invention, by forming a reflective film in parallel to the polarizing film at the corner of the beam splitter, the measurement light optical path and the reference light optical path are connected to the same optical element. Since the optical element passes through the same number of times, the influence of thermal expansion of the optical element can be reduced. Also, the influence of the tilt of the plane mirror is small.

Furthermore, in the present invention, power can be distributed much closer to the measurement surface and the reference surface than in the past, so the dead bus can be reduced and the influence of disturbances can be reduced.

Furthermore, in the present invention, since the reference light and the measurement light pass through the same path, they are affected by air fluctuations in the same way.
Errors are reduced.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the measurement light optical path of the interference optical system according to the present invention, FIG. 2 is an explanatory diagram showing the reference optical path of the interference optical system according to the present invention, and FIG. 3 is a schematic diagram of the polarizing beam splitter. FIG. 4 is an explanatory diagram showing the measurement light optical path of the interference optical system according to the present invention when the plane mirror is tilted; FIG. 5 is an explanatory diagram showing the optical path of the conventional interference optical system. 30...Polarizing beam splitter, 32...Switching wave plate, 34.36...Corner cube, 3
8... Polarizing film, 40... Reflecting surface, 42... Wave plate, 44... Reference plane mirror, 46... Moving plane mirror.

Claims (1)

[Scope of Claims] A polarizing beam splitter into which a laser beam having P-polarized light and S-polarized light is incident and which has a polarizing film arranged obliquely with respect to the laser beam incident direction; and a laser beam incident on the polarizing beam splitter. a first corner cube disposed on one side of the polarizing beam splitter in a direction orthogonal to the polarizing beam splitter; a first quarter-wave plate disposed between the polarizing beam splitter and the first corner cube; A second corner cube is disposed on the opposite side of the polarizing beam splitter from the first corner cube in a direction perpendicular to the laser beam incident on the polarizing beam splitter, and a second corner cube is arranged on the opposite side of the polarizing beam splitter to the laser beam incident side with the polarizing beam splitter in between. At the corner of the polarizing beam splitter sandwiched between the second quarter-wave plate, reference plane mirror, and movable plane mirror disposed on the opposite side, the second corner cube, and the second quarter-wave plate, A plane mirror interference optical system consisting of a reflective surface formed parallel to a polarizing film.