JPS59136604A - Multiple optical path laser interferometer - Google Patents

Abstract

PURPOSE:To improve resolving power for measuring length by disposing a quarter-wave plate between a composite prism which reflects two split beams by a plural number of times between two plane reflection mirrors and makes the same incident to a synthetic optical system and the plane reflection mirrors. CONSTITUTION:Laser incident light 1 is split to two parallel beams 2, 2 by a beam splitter (BS). The split beams are repeatedly reflected via a lambda/4 plate 13 between the respective faces in a composite prism 12 having reflection faces 26, 27 intersecting orthogonally with each other and plane mirrors 14, 15 in the sequence shown by the numbers in round circles. The inclination with the mirrors 14, 15 is absorbed by the reflections and the beams 29, 29 passing the same optical path as the optical path of incident light 2, 2 are emitted. The emitted beams are again made incident to the BS11 by which the beams are combined to exit light 30 parallel with the light 1. Since the plate 13 rotates 90 deg. the plane of polarization of the reflected light twice before and after by the plate 13, the loss of the light in the optical path is hardly generated. The length of the optical path is increased by multiplexing the optical path and the resolving power for measuring length is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-optical laser interferometer used, for example, in attitude measurement, precision positioning, and measurement of ultra-fine displacement in machine tools.

In general, Michelson type optical interferometers are often used for precision measurements, but in such Michelson interferometers, when the reflecting mirror is tilted, the original equi-floating interference fringes change accordingly. ... becomes a major error factor in the 1j length. If the inclination of the reflecting mirror further increases, even detection of interference fringes becomes difficult. In order to prevent the wavefront of the reflected light from being tilted due to the tilt of the reflecting mirror, a corner-keep prism is generally used, but manufacturing a corner-keep prism with high precision is not easy and is therefore expensive. There is a drawback. Additionally, corner keve prisms cannot be used in measurements that require the contact surfaces of the object to be measured and the reflecting mirror to exactly match, such as the measurement of the coefficient of thermal expansion using optical interferometry. .

An object of the present invention is to use a plane mirror that is inexpensive and has few restrictions on where it can be used, without using the corner keve prism, and to make length measurement errors due to inclination virtually negligible, thereby enabling high-precision measurement. The object of the present invention is to obtain a multi-path laser interferometer with a length n''.

Another object of the present invention is to multiplex the optical path in a Michaelnon interferometer and multiply the optical path length (2 times, 4 times, still 8 times) to significantly improve the length measurement resolution. The objective is to obtain an optical path laser interferometer.

In order to achieve the above object, the multi-path laser interferometer of the present invention splits the incident light from a laser light source into two parallel light beams, and combines the two light beams returning along the same optical path. an optical system that emits light; and a compound prism that causes the two light beams split by the optical system to undergo multiple (b) reflections between two flat reflecting mirrors and then enter the optical system again. , and a quarter wavelength plate disposed between the above-mentioned composite prism and a pair of plane reflecting mirrors.

Hereinafter, before describing embodiments of the present invention, the present invention will first be described in detail based on the first factor 6.

In the principle explanatory diagram of FIG.
3 is a quarter-wave plate, and 4 is a plane reflecting mirror. When these are arranged in the positional relationship shown in the figure, the laser incident light ■ and the emitted light beams ■ and ■ will always be parallel as shown in the figure. . That is,
In the above optical system, when the incident light (■) is perpendicular to the plane reflecting mirror 4, the reflected light (■) returns along the same optical path as the incident light (■), and the reflected lights (■, ■, ■) shown by broken lines in the same figure and An emitted light (2) is obtained, and this emitted light (1) is parallel to the incident light (2). Furthermore, when the plane reflector 4 is tilted clockwise by an angle θ, the reflected light from the plane reflector 4 is also tilted clockwise by an angle 2θ. After being sequentially reflected by the transparent surfaces 2 and 2 (reflected light ■, ■), the plane reflecting mirror 4 tilts in the counterclockwise direction by an angle 2θ, contrary to the above, so that the emitted light ■ becomes the incident light ■
It becomes parallel to .

As is clear from this, the BuC optical system described above functions similarly to a corner key prism, and therefore, by utilizing this optical system, the problem of the tilt of the reflecting mirror in the Michelnon type optical interferometer can be solved. I can do it.

Note that the arrows in the figure indicate the direction of travel of the light, and the intersecting lines and circles behind the arrows indicate that the light marked with these marks is polarized light parallel to the paper surface and polarization perpendicular to the paper surface. It shows. In addition, the quarter-wave plate 3 rotates the plane of polarization of the incident light and the reflected light on the plane reflecting mirror 4 by 90 degrees twice, causing almost no loss of light in the optical path. .

Next, embodiments of the present invention based on the above-described principle will be described with reference to FIGS. 2 to 6.

In the optical system shown in FIGS. 2 and 6, 11 is a beam splitter, 112 is a composite prism, 13! -14 wavelength plates, 14 and 15 each indicate a plane reflecting mirror.

The above beam splitter-II? 'i, Incident light (■) from a laser light source (not shown) is converted into two parallel beams (■).

(2) and synthesizes the reflected light that returns along the same optical path to form the emitted light [phase].
It is configured as an optical system equipped with 7.

As shown in FIG. 4, the composite prism 12 disposed next to the beam splitter 11 has a pair of polarizing semi-transparent surfaces 21 and 22 orthogonal to each other tilted at 45 degrees with respect to the incident light. It is composed of a multiple reflection section 20 provided as a mirror, and a pair of right angle prisms 24 and 25 disposed on the light source side of the multiple reflection section 20.

The right angle prism 24 has total reflection surfaces 26 orthogonal to each other.
and the total reflection surface 27 are tilted at 45 degrees with respect to the direction of the incident light (1), and one polarization semi-transparent surface 2 in the multiple reflection section 20 is formed.
2, the ridge line 28 between the total reflection surface 26 and the total reflection surface 27 when viewed from the light source side is located at the position corresponding to the ridge line 2. For one,
It is arranged so that it faces perpendicularly to the
In addition, the right-angle prism 25 has total reflection surfaces 29 and 30 that are orthogonal to each other, each inclined at 45 degrees with respect to the incident light (1), and one polarization semi-transparent surface 2 in the multiple reflection section 20.
], and the pair of total reflection surfaces 29, 3
The ridgeline 31 between 0 and 0 is arranged parallel to the ridgeline 23 of the multiple reflection section 20. Then, the composite prism 12 separates the pair of incident lights (1) and (2) coming from the beam splitter 11 between the polarizing semi-transparent surfaces 21, 22 and the plane reflecting mirrors 14 and 15. + b Return and reflect,
Increasing the optical path length by 8 times and plane reflection 1j414,1
By absorbing the slope of s, light parallel to the incident light ■, ■ is generated +? ! e
), [phase] is configured to be injected. Also,
The quarter wavelength plate 13 and the plane reflecting mirrors 14 and 15
are arranged in a direction perpendicular to the incident light (2).

In the multi-path laser interferometer with the above configuration, when the incident light 1 from the laser light source is incident on the beam splitter 11, the incident light (1) is divided into two parallel beams (2) and (2) by the semi-transparent mirror 16 and the total reflection mirror 17. and each enters the composite prism 12. A pair of light rays (■, ■) incident on the composite prism 12 are transmitted to each surface of the composite prism 12 and to the plane reflecting mirror x4.
15, and the inclination of the plane reflecting mirror 14°15 is absorbed by these reflections, and the incident light
The light ray [phase] passing through the same optical path as the beam exits as @, enters the beam sub 1) again and is synthesized, and exits as the emitted light ■ which is parallel to the incident light ■.

In the above interferometer, the composite prism 12 is configured as a combination of a multiple reflection section 20 and a pair of right angle prisms 24 and 25. The function to make parallel to 6
Since it has been expanded dimensionally, even if the plane reflecting mirrors 14 and 15 are tilted in any direction around an arbitrary axis p, the incident light (1) and the outgoing light [phase] will always be parallel. [Kai] As mentioned above, the light rays are reflected repeatedly between the composite prism 12 and the plane reflecting mirrors 14 and 15 an even number of times (two or four times) in both the horizontal and vertical directions, so the reflection There is no lateral shift in the optical axis of light.

The sub-length error associated with the inclination of the plane reflecting mirrors 14 and 15 in the interference it is proportional only to the square of the inclination angle and the amount of change in the interval between the two plane reflecting mirrors 14 and 15 (optical path length difference). becomes. Therefore, mll −1j due to the above slope
The error is very small and can be ignored in practical terms, so if the two mirrors 14 and 15 are brought close together and the optical path length difference is set to almost zero, the movement of the two mirrors 14 and 15 can be reduced. At this time, only the change in the interval (translational component) can be detected, regardless of its inclination. On the contrary, the plane reflector 14
, 15, if the phase of the interference light does not change even if either one or both of
15 coincide with each other, and the optical path lengths become equal. Using this fact, the above interferometer can measure the two mirrors 1
Regardless of the inclination of mirrors 4 and 15, those mirrors 14 and 15
It is possible to detect a point where the optical path length difference becomes zero when the optical path length difference becomes zero. Therefore, the above-mentioned interferometer is very useful for obtaining a reference when performing precision positioning, that is, a stable and accurate base point.

5 and 6 show a translational component detection section and a rotational component detection section in a second embodiment of the present invention.

The above-mentioned translational component detection section is for detecting only the translational component of the plane reflection mirror 44 regardless of its inclination, and as shown in FIG. Comprised of mirrors 43 and 44, the compound prism 41 is a semi-transparent mirror 4 that splits and combines light rays.
6, a prism section 45 having a total reflection mirror 47, and a multiple reflection section 4 having polarization semi-transparent surfaces 49 and 50 orthogonal to each other.
8.

Still, the rotational component detection section shown in FIG. 6 is superimposed on the paper with the translational component analysis detection section shown in FIG.
1. The quarter wavelength plate 42 and the plane reflecting mirror 44 are commonly used, and the plane reflecting mirror 43 is a plane mirror with unnecessary parts removed as shown in FIG. 7, and the translation of the plane reflecting mirror 44 is Regardless of the displacement, only the rotational component, ie, the magnitude of the inclination, is detected.

In an interferometer with such a configuration, the incident light from the laser light source is divided into two parts, and the divided parts are divided into a pair of parallel incident lights to the prism 41 as shown in FIGS. 5 and 6.
(1) If the incident light enters the mirror, the incident light is split into two beams (2) and (2), respectively, and then passes along the optical path between the polarization semi-transparent surfaces 49, 50 of the multiple reflection section 48 and the plane reflecting mirrors 43, 44. The reflection that doubles the length is repeated, and the emitted light beams ■ and ■ are emitted parallel to the incident beams ■ and ■. As a result, if one of the plane reflecting mirrors 43 is in a fixed state, the above-mentioned emitted light (2).

The translational component and rotational component of the plane reflecting mirror 44 are detected independently by (2). Therefore, the interference side is extremely useful for comprehensive measurement of movements of precision fine movement tables and the like.

According to the present invention, the following effects can be expected.

(1) Even if the plane reflector that repeatedly reflects the laser beam is tilted, the wavefront of the interference light will not tilt and the optical axis will not shift.

(2) Since the length measurement error is made proportional to only the square of the inclination of the plane reflector, it is possible to perform measurements under conditions that cannot be measured with a normal Michelson interferometer, that is, one or both of the pair of plane reflectors. A highly reliable sub-head is possible even when performing a movement in which the Y-axis is tilted and the Y-direction of each other is deteriorated.

(3) Since the laser beam is multiple-reflected between the polarizing beam splitter and the plane reflecting mirror, the optical path length can be multiplied by 2, 4, or 8 times, and optical heterodyne interferometry can be applied. Therefore, ultra-high resolution length measurement is possible.

(4) Since an optical system having the same function as a corner-keep prism is used, optical adjustments can be made extremely easily.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of the present invention, FIGS. 2 and 6 are a plan view and a front view of an embodiment of the invention, respectively, FIG. 4 is a perspective view of the prism, and FIGS. 5 and 6 are FIG. 7 is a cross-sectional view of different parts of the second embodiment of the present invention, and FIG. 7 is a front view of the plane reflecting mirror in the second embodiment. designated agent

Claims (1)

[Claims] 1. An optical system that splits the incident light from a laser light source into two parallel light rays and combines the two light rays that return along the same optical path to form an output light, and the above optical system splits the field of light into two parallel light rays. A composite prism that causes the two light beams to be reflected multiple times between two flat reflecting mirrors and then enters the optical system again; A multi-path laser interferometer comprising a quarter-wave plate arranged.