CS201976B1 - Optical system of the detection unit for the laser interferometer - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical assembly of a detection unit for a laser interferometer.

A laser interferometer is a device that is used to accurately measure lengths and other geometric quantities. It works on the principle of an interferometer and usually uses a single-frequency laser as the radiation source. To determine not only the magnitude, but also the sense of motion of the moving part of the interferometer, the interference of two circularly polarized beams is used, which makes it possible to obtain two signals in the quadrature which control the logic of the direction of motion resolution. To obtain these signals, a detection unit is used in which the beam of beams exiting the interferometer is again divided to obtain two signals in the quadrature scanned by the detectors. A suitable frequency shall be selected from each beam so that the resulting signals on the detectors are at a phase shift of 90 ° (in quadrature).

The present arrangement of detection units usually uses two dividing plates with so-called approximately non-polarizing layers which divide the beams emanating from the interferometer and the selection of suitable frequencies is made in each divided beam by means of polarizing filters behind which detectors are located. The disadvantage of this arrangement is that the polarization filters have significant losses and attenuate the beams incident on the detectors. The use of polarizing filters (polarizers) further has the disadvantage that it merely suppresses and does not allow the orthogonal components of the circularly polarized beams exiting the interferometer to be utilized. For both these reasons, the separation efficiency in the prior art detection unit arrangement is low. The current detection units are also not universal and do not allow the use of interferometers working with orthogonal linearly polarized beams.

These previous disadvantages are overcome by the optical arrangement of the detection unit for a laser interferometer consisting of an approximately non-polarizing separating plate, behind which at least two detectors are arranged in the axis of the divided beams. The essence of the invention of the detection unit is that between the partition plate and the detectors there are polarizing dividers whose dividing planes are rotated by an angle of 45 ° in space. The polarizing dividers may be formed by Mac-Meil prisms, one of which is ground into a cylindrical shape with an axis coincident with the axis of one split beam and is rotatable about its axis. The detection unit is equipped with a replaceable quarter-wave plate at the inlet.

The main advantage of the detection unit is that it reduces losses in beam splitting to almost zero, allowing the use of both orthogonal components of the circularly polarized beam beam from the interferometer. The detection unit allows the use of different types of interferometers operating with both circularly polarized beams of opposite orientation and orthogonal linearly polarized beams.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated in greater detail by the accompanying drawing, in which an example of an optical arrangement of a detection unit is schematically indicated.

In the axis of the beam from the laser interferometer 1, there is an approximately non-polarizing separating plate 3 behind the quadrilateral exchange plate 2. In the axis of the first divided beam a first detector 6 is located after the first linear delay plate 4. a second linear delay plate 7, a second polarizing divider 8 and a second detector 9 are arranged one behind the other. For easy alignment of the divider planes of the polarizing divider 5 and 8, the first polarizing divider 5 or the second polarizing divider 8 is formed as a cylinder with an axis coincident with the split axis and the cylindrical polarizing divider is rotatably mounted about its axis.

At the input of the detection unit is an easily removable quarter-wave j delay plate 2 which allows the use of different types of interferometers working with both circularly polarized beams of opposite orientation as well as orthogonal linearly polarized beams. The phase shift of the first approximately non-polarizing divider plate 3 can be compensated by linear delay plates 4 and 7 with an azimuth Θ - 0 ° and a phase delay equal to the respective phase shift of the divider plate 3 for passage or reflection. The selection of the appropriate frequency for the split beam providing the signal in quadrature is done by appropriately rotating the planes of the two polarizing beam splitters used relative to each other. Easy rotation is possible by making one of the polarizing dividers 5 and 8 cylindrical.

The optical arrangement of the detection unit operates as follows:

From the laser interferometer L11, the beam of light is typically in the form of two circularly polarized beams of opposite orientation. If, in some types of interferometers, the output beam is in the form of two orthogonal, linearly polarized beams, a linear quarter-wave delay plate 2 is inserted at the input of the detection unit, which converts the output beam to a unified type, ie circularly polarized beams of opposite orientation.

This beam (i.e., united beams from the interferometer, reference and specific, circularly polarized with opposite orientation) is first divided by approximately non-polarizing dividing plate 3 into two beams. These two beams proceed to polarizing dividers 5, 8. It is usually necessary to compensate the phase shift for reflection by the linear delay plate 4 in the path of one split beam and the phase shift for the passage of the linear delay plate 7 in the path of the second split beam. The azimuth of the delay plates 4, 7 is zero with respect to the plane of incidence of the separating plate 3. After passing through the linear delay plates 4, 7, the divided beams impinge on the polarizing dividers 5, 8 and 7, respectively. are further divided by each divider 5, 8 into two linearly polarized beams, whose oscillation planes are perpendicular to each other. By rotating the dividing planes of the two polarizing dividers 5, 8 at different spatial angles to each other, signals with any phase from zero to 360 ° can be obtained from the detectors 6, 9. By rotating the two polarizing dividers 5, 8 so that the dividing planes of the polarizing dividers 5, 8 enclose a spatial angle of approximately 45 °, we get signals on the detectors 6, 9 phase shifted by 90 (in quadrature) needed to distinguish the moving direction interferometer. The other two beams, starting from the polarizing dividers 5, 8, can advantageously be used, for example, to obtain 180 ° phase shift signals relative to the original signals.

Claims (3)

SUBJECT OF THE INVENTION Optical assembly of a laser interferometer detection unit, consisting of a non-polarizing beam plate, behind which at least two detectors are arranged in the axis of the divided beams, characterized in that polarizing dividers are arranged between the beam plate (3) and the detectors (6 and 9). (5 and 8), whose dividing planes are rotated at an angle of 45 ° in space. 2. The optical system of the detecting unit of claim 1, wherein one of the polarizing dividers (5, 8) is ground into a cylindrical shape with an axis coincident with the axis of one split beam, and the cylinder is rotatably mounted about its axis. 3. The optical system of the detection unit according to claim 1, characterized in that the detection unit is provided with a replaceable quarter-wave plate (2) at the inlet.