SU1168800A1 - Two-step interferometer - Google Patents

Abstract

A two-stage inteferometer includes a laser light source (1) and a beam splitter (2) having a partially metallised surface (3) which acts as an interference plane for producing two separate light beams (4 and 5). A measuring reflector (6) and a reference reflector (7) are disposed in the paths of the beams (4 and 5), respectively. The beam splitter (2) has on each side of the surface (3) a further beam-splitting, partially metallised surface (8,9), the latter surfaces lying symmetrically of the interference plane (3). A deflecting element, which can comprise a one- part element (13) or multiple elements (11, 12-see Fig. 2 not shown), is disposed at the end of the beam splitter (2) facing the measuring and reference reflectors (6,7). The deflecting element has optically effective reflective surfaces (14, 15) which align the light beams (4,5) so that the latter are mutually parallel, and has a beam exit surface (16) extending at 90 DEG to the interference plane (3). <IMAGE>

Description

The invention relates to a two-stage interferometer, intended, in particular, for length measurements, while the two-way interferometer works with two interference patterns to determine the direction of changes in length.

In the description of the invention to the patent • GDR No. 111 993, cl. 42 V 8/02, 1974 an optical interferometer is described for creating two interference patterns, with the light beam splitter having a dividing face on both sides and mainly paral ~ 15

It is suitable for it on one additional dividing face, partially covered with a mirror layer. These edges of the light components of both

partial interference beams ί 20

the pictures are rejected and once again interfere with each other.

However, in a two-stage interferometer, which is based on the Michelson principle, in order to optimally determine the reference point ^{25 of the} interferometric measurement, an introductory prism is provided, causing a highly asymmetric course of the rays. The most favorable position of the reference point and symmetry in meth ³⁰ rologicheski sensitive parts of the interferometer are mutually exclusive.

So, for example, in the resolution range of 1SG® — 10 ' ⁹ m for a long measurement time it is impossible to make

2

to conduct measurements stably with respect to the zero point, since the parts of the interferometer that determine the optical path length, in the case of thermal perturbations, allow various changes in the optical path length in the measuring and reference paths of the rays.

All these disadvantages reduce the accuracy of the measurement.

The purpose of the invention is to eliminate the drawbacks of the prior art and improve the accuracy with interferometric measuring systems.

This goal is achieved by the fact that, in a two-stage interferometer, designed, in particular, to measure length, containing a light source, a light beam splitter with a separating face partially covered with a mirror layer to 'create two separate light beams, the measuring reflector located during the first light beam, and the reference reflector, located during the second light beam, the light beam splitter has on both sides of the face, which is the plane of interference, one further dividing faces, partially covered with reflective layer, wherein these edges are disposed symmetrically The ratio, respect to the plane of interference, at the end of the beam splitter facing the measuring and this ^-

3

1168800 4

A single-sided deflecting element or deflecting element composed of several single prisms that are independently adjustable from one another; the deflecting element has optically active reflective edges that parallel light beams and form the same angles with the plane of interference; beam output perpendicular to the plane of interference.

At the same time, the light beam splitter, at the end facing the measuring and reference refletors, has a cutting surface on which the deflecting element is located and which is perpendicular to the plane of interference.

Single prism diverter 20

elements can be located symmetrically with respect to the plane of interference and connected in a клон declining prism, with the faces of the exit of the beam of single prisms approximately 25

located in a plane perpendicular to the plane of interference.

In a two-stage interferometer, the face, which is the plane of interference, and the separating faces, 30 parallel to it, are elongated in the direction of the measuring and reference beam paths, and on the elongations of these faces, not completely covered with a specular layer, output prisms are located, which deflect and direct light beams in parallel .

The proposed device achieves the parallel nature of the measuring and reference beam paths in up to two-stage interferometers and the symmetry between these beam paths inside the light beam splitter, which causes 45 instruments equipped with such interferometers to be more accurate, as well as for a large measurement time The reference beam paths inside the interferometer remain constant, despite the existing temperature changes. In addition, the entire course of the interferometer beams is insensitive to insignificant inclinations of the interferometer. The individual parts of the interferometer have 55 simple designs ..

FIG. 1 shows a light beam splitter with a single deflection prism; in fig. 2 - the same, with a composite deflecting prism; in fig. 3 - the same, with elongated faces.

Two-stage interferometer

(figure 2), used, in particular, to measure lengths and displacements, contains a laser as a source

1 light, a splitter 2 light beam with a separating face partially covered with a mirror layer serving as the interference plane 3 for creating two separate light beams 4 and 5, and reflectors 6 and 7 located during these light beams 4 and 5. So, in the course of the light beam 4, a movable measuring reflector 6 is located, and in the course of the light beam 5 there is a fixed reference reflector 7, and these reflectors are mainly made in the form of mirror triple prisms. On both sides of the plane 3 interference in the splitter

2 light beams are provided along one additional separating face 8 and 9, partially covered with a mirror layer, which are parallel to and symmetrical with respect to the interference plane 3. The splitter 2 of the light beam at the end, facing the measuring and reference reflectors 6 and 7, has a cut surface 10 on which a one-piece deflecting element (FIG. 1) or a deflecting element consisting of several single prisms 11 and 12 arranged independently of one another (figure 2). The deflecting element 13 has optically active reflective faces 14 and 15, which with the plane 3 of the interference mainly constitute the same angles. These angles are calculated so that the light beams 4 and 5 of the measuring and reference beam paths are parallel to one another.

The possibility of adjusting the reflective edges 14 and 15 in the case of the embodiment according to FIG. 2 within certain limits is determined by the use of the thickness of the bonding layer between the single prisms 11 and 12 and between the cut surface 10 and the single prisms 11 and 12. The deflecting element 13 has a beam exit face 16 perpendicular to the interference plane 3. In the device of figure 2

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1168800

The faces 17 and 18 of the beam exit and the single prisms 11 and 12 are provided so that they are approximately located in a plane perpendicular to the plane of interference 3.

The design of the splitter 19 of the light beam of the two-stage interferometer according to FIG. 3 is most preferred. The splitter 19 of the light beam is composed of two plane-parallel plates 20 and 21, and the edges 22-24 in the part that is definitive for the splitter of the light beam are partially covered with a mirror layer. The edges 22-24 in the direction of the measuring and reference reflectors 6 and 7 are elongated, and these extensions are not fully reflected by the mirror layer. On the elongations of the faces 22 and 24 are output prisms 27 and 28, which deflect and parallel the light beams. Face 23. is represented by-. The plane of interference is similar to that shown in FIG. 1 and 2.

The installation and balancing of the measuring and reference beam paths inside the interferometer (Fig. 3) are achieved by mutual alignment of the outputting prisms 27 and 28, which are moved along the elongations of the faces 22 and 24 and tilted when using the thickness of the gluing layer.

Based on the design of the device according to FIG. 3 describes the function of a two-stage interferometer, similar to the function of the devices of FIG. 1 and 2. The collimated light beam from a laser source -.

 1 light through the inserting prism 29, located on the splitter 2 of the light beam (19 according to Fig. 3), is introduced into the upper part of the splitter. The insertion prism '29 is provided in order to equalize the directions of the incident light beam and the light beams 4 and 5, which is necessary for some measurement purposes. In addition, the light beam can be introduced into the splitter 2 (19 according to FIG. 3) of the light beam and with the help of prism 30. The introduced light beam passes through the splitting layer of face 23 and is divided into two light beams 4 and 5, representing measuring and reference strokes rays. Light beams 4 and 5 through outgoing prisms 27 and 28 exit the interferometer, measuring 6 and reference 7 reflectors are moved to the lower part of the light beam splitter 2 (19 according to Fig. 3) .and in the splitting layer the face 23 representing the interference plane interfere. From there, partial beams containing already interference information (according to the well-known two-step principle), through the splitting layers of the faces 22 and 23 and the prisms 30 and 31 arrive at receivers 32 and

33 signals or as a reflected light component from the splitting layers of the faces 22 and 24 a second time, they interfere in the plane of the face 23 and from there get to the receivers

34 and 35 signals.

It is recognized as an invention according to the results of the examination carried out by the Office for the Invention of the German Democratic Republic.

1168800

FIG. 2

Claims (4)

1. A TWO-SPEED INTERFEROMETER, designed in particular for length measurements, contains a light source, a light beam splitter with a separating face partially covered with a mirror layer to create two separate light beams, a measuring reflector located during the first light beam, and a reference reflector, located during the second light beam, the splitter · light beam has on both sides of the edge, which is the plane of interference, on one additional separating face, partially covered with a mirror layer, and these faces are located symmetrically relative to the plane of interference, distinguished by the fact that at the end of the light beam splitter facing the measuring and reference reflectors, whole. a deflecting element or the deflecting element is composed of several single prisms, adjustable independently of one another, the biasing member has an optically active reflecting faces which is directed parallel to the light beams and make with the plane of the interference ^odi-: Nakova angles and beam exit face, perpendicular to the interference planes . 1168800 2. The interferometer according to claim 1, characterized in that the light beam splitter at the end facing the measuring and reference reflectors has a cut surface on which the deflecting element is located and which is perpendicular to the plane of interference. 3. Interferometer according to claims 1 and 2, characterized in that the single prisms of the deflecting element are arranged symmetrically relative to the plane of interference and are connected in the deflecting prism, and the faces of the beam exit of single drism are approximately located in a plane perpendicular to the plane of interference. 4. The interferometer according to claim 1, characterized in that the face, which is the plane of interference, and the separation faces parallel to it are elongated in the direction of the measuring and reference light paths ^ and on the elongations of these faces that are not completely covered with a mirror layer, output prisms that deflect and parallel light beams. I