DD296753A5 - POLARIZATION BEAM DIVIDER FOR A TWO-FREQUENCY DIFFERENTIAL INTERFEROMETER WITH EIGHT-LIGHT LIGHT PATH AND THE VOLUMES OF WHICH IS LOW - Google Patents

Abstract

The invention relates to a polarization beam splitter for a two-frequency differential interferometer with eightfold light path. The invention consists in dasz in a polarization beam splitter for a two-frequency differential interferometer with eightfold 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 joining surface (3), on which a 1/2 plate (6) is fixed, in which the second prism (2) is attached as 45 °. Rhombusprisma is formed, thez to the Fuegeflaeche (3) parallel surface * which is provided with a polarization-dividing layer, a Halbwuerfelprisma (8) is attached, at its parallel to the light incident direction (4) Kathetenflaeche a triple strip (9) is worked, whose projection of its roof edge (10) is perpendicular to the light incident direction (4) in the light incident direction (4), dasz to the senk a phase plate (12) with a defined phase shift is fixed, and that on the phase plate (12) a triple strip (13) is fixed, the projection of its roof edge (14 ) is perpendicular to the light incident direction (4) in the light incident direction (4). FIG {polarization beam splitter; Two-frequency differential interferometer, eightfold; light path; Prism; Fuegeflaeche; l / 2 plate; Roof edge; Tripelstreifen; Projection}

Description

Explanation of the essence of the invention

The invention has for its object to provide a Polarlsatlonastelltellur for a two-frequency differential interferometer 7.U, dosson optical effect is realized with a small number of optically effective glass / air transitions and whose volume is low. Üie object is achieved in that in a polarization beam splitter, which consists of two cemented prisms, which are provided with a polarisatlonsteilenden layer Fügeflächon inclined at 45 ° to the direction of light incidence, the lying in the direction of light first prism is provided with a plane parallel to the joint surface on which a λ / 2 plate is attached.

Furthermore, according to the invention, the second prism is designed as a 4S ° rhombic prism, wherein a half-cube prism is attached to the surface lying parallel to the joining surface, which is also provided with a polarization-forming layer, on the surface of the catheter parallel to the direction of light incidence a tuft is attached Projection of its roof edge is perpendicular to the light incident direction in the light incident direction.

Furthermore, a phase plate with a defined phase shift is fixed to the plane perpendicular to the direction of light incidence of the second, formed as a rhombic prism prism, a phase plate is fixed to the a triple strip is fixed, the projection of its roof edge perpendicular to the light incident direction in the light incident direction 'Hegt.

For an interferometer structure, it is structurally advantageous if in each case a λ / 4 plate is cemented to the plane facing away from the light source plane surface of the rhombic prism and the half-cube prism.

With the polarization beam splitter, a two-frequency differential interferometer system can be constructed, particularly for measuring the distance between a reference mirror and a measuring mirror moving in the same axis.

The beam path emanating from a two-frequency laser is split by the polarization beam splitter in cooperation with the reference and measuring mirrors in a reference beam and a measuring beam with a different frequency.

Both beam paths have an optical path length difference which corresponds to the distance between the reference mirror plane and the plane of the mirror plane.

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

The Pülarisationsstrahlenteiler causes except said path length difference, both beam paths have the same optical path lengths. There are thus no measurement errors if thermal changes cause changes in the length of the polarization beam splitter. The polarization beam splitter is to be fabricated in a block, so that no displacements or tilting of optical components against each other occur. The beam guidance takes place with a minimum number of optical components in a confined space, it represents an optimum in terms of space utilization.

Ausführungsbulspiel

In the drawing, an embodiment of the invention is shown in two views.

Thereafter, the polarization beam splitter consists of a half-cube prism 1, which is cemented on its Hypothenusenfläche with a 45 ° -Rhombusprisma 2. At least one of the planar joining surfaces 3 is coated with a polarization-dividing coating, wherein the joining surfaces 3 are arranged at an angle of 45 ° to the light incident direction 4. The half-cube prism 1 has a plane surface 5 parallel to the joining surfaces 3, to which a λ / 2 plate 6 is sprinkled. A second half-cube prism 8 is cemented with its hypotenuse surface to the planar surface 7 which lies parallel to the joining surface 3 and which is likewise coated with a polarization-dividing coating, the catheter surface lying parallel to the direction of light incidence 4 being in the form of a triple strip 9. The projection of the roof edge 10 of the triptych strip 9 perpendicular to the light incident direction 4 lies in the light incident direction 4 itself. A phase plate 12 which has a defined phase shift is cemented to the plane surface 11 lying perpendicular to the light incidence direction 4. On the phase plate 12 a triple strip 13 is exploded, the projection of its roof edge 14 in the direction perpendicular to the light incident direction 4 is also in the light incident direction 4. At the side facing away from a two-frequency He-Ne laser 15 flat surfaces 16,17 of the Rhombusprismas 2 and the half-cube prism 8 are each a λ / 4 plate 18,19 angekittet.

To realize a two-frequency differential interferometer, the laser 15 is further arranged in the beam path:

a fixed, partially coated reference mirror 20 and a measuring mirror 21 movable in the light incident direction 4, the mirror surfaces of which are aligned parallel to the plane surfaces 16, 17, and a photoreceiver 22.

In this interferometer arrangement, the beam splitter functions as follows:

The two generated by two-frequency He-Ne laser 15 two offset by 90 ° linearly polarized partial beams 23,24 are separated by the polarization-sharing coating on the joining surfaces 3 in a Meßstrahlengang 25 and a reference beam path 26. The partial beam polarized parallel to the joint surface 3 runs in the interferometer plane path along the following points of the optical axis:

A, B, C, D, C, E, F ', G', F ', E, H, E, F ₁ A', Γ, A 'and the photoreceptor 21st

The partial beam polarized perpendicular to the joining surface 3 has the following profile:

A, K, A, F, E ', L', E ', F, M, F, E', C, N ', C, B', A 'and the photoreceptor 21.

Depending on the direction of polarization, the partial beams 22, 23 are transmitted through the polarization-splitting covering to the joining surface 3 through the joining surface 3 or deflected by 90 °. Outside the beam splitter between λ / 4 plate 10 and reference mirror 20 and measuring mirror 21, the partial beams are circularly polarized. The thickness of the λ / 2 plate 6 is dimensioned so that the polarization plane of the respective partial beam is rotated by 90 °.

The phase plate 12 has a thickness such that the respective partial beam 23,24 causes a rotation of the polarization plane by 90 ° when passing through the phase plate twice.

Claims (2)

1. A polarization beam splitter for a two-frequency differential interferometer with eightfold light path, consisting of two cemented prisms, which are inclined with their planar joining surfaces at 45 ° to the direction of light incidence, wherein at least one joining surface is provided with a polarization-dividing layer, characterized in that the first prism (1) lying in the light incidence direction (4) has a plane surface (5) parallel to the joining surface (3), on which a λ / 2 plate (6) is fastened, in that the second prism (2) is designed as 45 ° Rhombusprisma is formed that at the joining surface (3) parallel surface (7), which is provided with a polarization-dividing layer, a half-cube prism (8) is fixed, at its parallel to the light incident direction (4) lying Kathetenfläche a triple strip (9) is working, whose projection of its roof edge (10) perpendicular to the direction of light incident light (4) in the direction of light incident (4) that the perpendicular a phase plate (12) with a defined phase shift is attached to the light incident direction (4) lying flat surface (11) of the second prism (2), and that on the phase plate (12) a triple strip (13) is fixed, the projection of its roof edge (14) perpendicular to the light incident direction (4) in the light incident direction (4). 2. Polarization beam splitter according to claim 1, characterized in that facing away from the light source (15) flat surfaces (16,17) of the rhombic prism (2) and the half-cube prism (8), which are perpendicular to the light incident direction (4), in each case a λ / 4-plate (18, 19) are cemented. For this 1 page drawing Field of application of the invention The invention is applicable to beam splitting in Zwel frequency differential interferometers, in particular for the interferometric measurement of traverse paths, angles and refractive indices with high resolution and accuracy. Characteristic of the known state of the art Polarization beam splitters for two-frequency differential interferometers have the task of splitting the two frequencies of a laser beam into two separate sub-beams, to guide these sub-beams in a measuring and reference beam path and to reunite on a receiver surface as the interference plane. Furthermore, it must be ensured by the beam splitter arrangement that there is no feedback of the measurement and Referanzstrahlengänge in the laser, and that tilt invariance exists for the movable measuring mirror. For measurement and reference beam must be the same optical paths. EP0244275A2 discloses an angle measuring interferometer in which a beam splitter is included which, in addition to a splitting 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 puttied on a catheter surface of a half cube. In the flat mirror interferometer described in EP0281385A2, two λ / 4 plates and a triple prism are sprinkled or cemented to different catheter surfaces of a splitter wafer. In a further variant of this plane mirror 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 dejustieren the beam path. The number and complexity of the applied optical components, as well as their size and weight require high costs in the manufacture of such beam splitter. Furthermore, the assembly of the interferometer is complicated, in particular when many individual components in the beam path have to be adjusted to each other. The beam splitters described above are provided for interferometers with fourfold light path. For interferometer with eightfold light path these beam dishes are not applicable. With a conversion of said beam splitter from four times to eight times the light path by supplementing with other optical elements, the disadvantages mentioned would become even more apparent. 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.