DD296755A5 - POLARIZATION BEAM DIVIDER FOR A TWO-FREQUENCY DIFFERENTIAL INTERFEROMETER WITH FOUR-LIGHT LIGHT PATH - Google Patents

Abstract

The invention relates to a polarization beam splitter for a two-frequency differential interferometer with fourfold light path. The invention consists in dasz in a polarization beam splitter for a two-frequency differential interferometer with fourfold light path, consisting of two cemented prisms, which are inclined with their plane Fuegeflaechen by 45 to the light incident direction, wherein at least one Fuegeflaeche is provided with a polarization-splitting layer in that the first prism (1) lying in the direction of light incidence (4) has a plane surface (5) parallel to the surface (3), on which a 1/2 plate (6) is fixed, and perpendicular to the direction of light incidence (4). the second prism (2) is designed as a triple strip (7), wherein the projection of the roof edge (8) of the triple strip (7) is perpendicular to the light incident direction (4) in the direction of light incidence (4). FIG {polarization beam splitter; Two-frequency differential interferometer, quadruple; light path; Prism; l / 2 plate; Tripelstreifen; Roof edge}

Description

bostoht, doron with olnor polarization-stollondon layer vorsohono piano Fügoflächon be 46 ° to Lichtolnfallsrnchtung lying, the lying in Llnhtoinfallarlchtung-orsto prism with olnor to the FügeflScho parallel Mölling Plan flücho vereohon is on which a λ / 2-Platto is attached.

Furthermore, according to the invention, the second prism is formed in the direction perpendicular to the direction of light incidence as Tripolstroifon, wherein the projection of Dachkanto dos Trlpolstrolfons is perpendicular to Lichtolnfallsrlchtung in Llchdinfallsrichtung. For olnon Intor foromotoraufbau it is structurally advantageous if at the von dor light source nbgowand'.on plane surface of the second prism a λ / 4 Platto is cemented. With the polarization beam splitter, a Zwel-Froenen-Differentlal · Intorforomotorsystom can be constructed, in particular for the measurement of the distance between a Roferonspirogel and a measuring spine moving in the same axis. The beam path emanating from an olnem two-freonzonlasor is gated by the polarization beam interferometer into a Roferon beam and a measuring beam with a different frequency in cooperation with the reference mirror and the target mirror.

Optical light paths have an optical longitudinal amplitude that corresponds to the distance between the reflector and the master log level.

The optical path length is four times the distance between the reference plane and the mirror plane, because the path is traversed four times by the light.

The polarization beam splitter causes outside of said path length differences * both beam paths to have the same optical path lengths. There are thus no measurement errors when thermal changes cause changes in the length of the polarization beam dish. The polarization beam plate Is to be manufactured in a block, so that no displacements or tilting of optical components against each other occur. The beam guidance takes place with minimal number of optical components in the narrowest spaces, sio represents an optimum in terms of space utilization.

Ausführungsbelsplel

In the drawing, an embodiment of the invention is shown in two views. Thereafter, the Polarisatlonsstrahlenteiler consists of a first prism 1 and a second prism 2, which are cemented together like a conventional beam splitter cube on the flat joining surfaces 3. At least one of the joining surfaces 3 is coated with a polarlsationstoilondon coating, wherein the pad surfaces 3 are arranged at an angle of 45 ° to the light incident direction 4. The prism 1 has a plane parallel to the joining surfaces 3 plane surface δ, to which a λ / 2 plate 6 is blasted. Senkrocht to the light incident direction 4, the prism 2 is formed as Trlpelstreifen 7, wherein the projection of the roof edge 8 of Trelpelstroifens 7 in the direction perpendicular to the light incident direction 4 in the light incident direction 4 itself. Prism 2 has a Plenflächo 9 lying in the direction perpendicular to the light incident direction 4, to which a second λ / 4 plate 10 is blasted. In order to realize a two-frequency differential interferometer, a two-f-pitch He-Ne laser 11, which supplies two Toll beams 12, 13 with a low frequency difference, offset by 90 ° and also linearly polarized, is further arranged in the beam path fixed reference mirror 14 and a measuring mirror 15 movable in the direction of light, whose mirror surfaces are aligned parallel to the plane surface 9, and a photoreceptor 16. In this arrangement the beam splitter functions as follows:

The polarized sub-beams 12,13 are separated by the polarization-forming coating on the joining surfaces 3 in a Meßstrahlengang 17 and a Reforonzstrahlengang 18. The parallel to the joining surface 3 polarized partial beam 12 is reflected at this. It passes through prism 1 on the λ / 2 plate 6, whose thickness is such that the plane of polarization of this partial beam is rotated by 90 °, so that the partial beam after a 90 ° deflection by the polarization-dividing coating on the joint surface 3 unhindered can pass through. This partial beam continues to pass through the λ / 4 plate 10 and now passes circularly polarized on the measuring mirror 15th

From the measuring mirror 15, this partial beam is reflected in itself, passes through a second time the λ / 4 plate 10 and is reflected as a linearly polarized partial beam whose polarization plane is rotated relative to its initial state by 90 °, at the polarization-splitting coating in the direction of the triple strip 7.

By multiple reflection in the triple strip 7 of the partial beam gets a lateral offset, is deflected at the joining surface 3 again by 90 ° in the direction of the measuring mirror 15 and reflected therein. The λ / 4 plate 10 is passed through twice, whereby the plane of polarization of the partial beam rotates by SO °. After further reflections at the joint surface 3 and in the triple strip 7, the partial beam reaches the receiver 16.

Perpendicular to the joint surface 3 polarized partial beam 13 is transmitted through the polarization-dividing coating passes, after passing through the λ / 4 plate 10 directly to the reference mirror 14 and is reflected in this in itself. By passing twice through the λ / 4 plate, the plane of polarization of this partial beam is rotated by 90 °, so that it is reflected at the joint surface 3 in the direction triple strip 7. After multiple reflection in the triple strip 7, the partial beam is again reflected at the joining surface 3 in the direction of the reference mirror 14. On the way back from the reference mirror 14, the partial beam passes through the λ / 4 plate 10 for the fourth time so that the partial beam passes through the 90 ° rotation of the polarization plane unhindered by the polarization-splitting surface of the joining surface 3. After a 90 ° deflection on the λ / 2 Platto 6 with 90 ° - rotation of the plane of polarization of the partial beam is reflected at the joint surface 3 and also passes to the receiver 16. In the receiver plane, the beidon Toilstrahlen interfere.

Claims (2)

1. polarization beam plate for elnZwel-froenen differential interferometer with fourfold light path, consisting of two cemented prisms, which are inclined with their planar joining surfaces by 45 ° to the light incident direction, wherein at least one joining surface is provided with a polarization-dividing layer, characterized in that the in the light incident direction (4) lying first prism (1) has a joining surface (3) parallel planar surface (5) on which a λ / 2 plate (6) is fixed, and that in the direction perpendicular to the light incident direction (4) the second Prism (2) is designed as triple angle (7), the projects of the roof edge (8) of the triple strip (7) is perpendicular to l.ichteinfallsrichtung (4) in the direction of light incidence (4). 2. Polarization beam splitter according to claim 1, characterized in that on the from the light source (11) facing away from plane surface of the second prism (2) which is perpendicular to the light incident direction (4), a λ / 4 plate (10) is cemented. For this 1 page drawing Field of application of the invention The invention is applicable to beam splitting in Zwol-Frequency-Differential-Interferometome, especially for interferometric measurement of traverse paths, angles and refractive indices with high resolution and accuracy. Characteristic of the known state of the art Polarization beam splitter for two-frequency-Dlfferential-interferometer have the task of splitting the two frequencies of a laser beam into two separate sub-beams to guide these Tollstrahlen in a measuring and reference beam path and reunite on a receiver surface as Intorferanzbene. Furthermore, it must be ensured by the beam splitter arrangement that there is no feedback of the measuring and reference beam length in the laser, and that tilt invariance exists for the movable measuring mirror. For measurement and reference beam must be the same optical paths. In EP 0244275A2 an interferometer for angle measurement is described, in which a beam splitter is included, which in addition to a disc cube for beam splitting includes a shear plate, two λ / 2 plates, a λ / 4 plate and a retroreflector. These components are each individually manufactured components, which are arranged separately in the beam path. The retroreflector is cemented on a catheter surface of a half cube. In the flat mirror interferometer described in et 0281385 A2, two λ / 4 plates and a triple prism are sprinkled or cemented to different catheter surfaces of a splitter cube. In a further variant of this plane rake interferometer, the half-cube prism of the splitter cube facing the light source has a plane surface inclined to the light direction by 45 °, and a λ / 4 plate is additionally arranged between the triple prism and the second half cube prism. These solutions have the disadvantage that they are not optimal in terms of reliability and economy. The reliability is impaired by the fact that a variety of used optical components with glass / air transitions, reflecting surfaces, glass streaks, etc., which are deformed by the system running laser wavefronts, the laser radiation by reflections, scattering, absorption and polarization losses of energy loses, and that thermal influences on the components misalign the beam path. The number and complexity of the optical components used, as well as their size and weight, cause high costs in the manufacture of such beam splitters. Furthermore, the assembly of the interferometer is complicated, in particular when many individual components have to be adjusted to one another in the beam path. Object of the invention The aim of the invention is a reduction of the effort and an improvement of the optical properties of a polarization beam splitter. Explanation of the essence of the invention The invention has for its object to provide a polarization beam splitter for a two-frequency differential interferometer whose optical effect is realized with a small number of optically effective glass / air transitions. The object is achieved according to the invention in that, in the case of a polarization beam splitter, which consists of two cemented prisms