SU1755041A1 - Interferometer for testing surface shape - Google Patents

Abstract

The invention relates to a measurement technique, can be used in the inspection of optical components with elliptical and hyperbolic surfaces and allows to improve the accuracy and performance of monitoring elliptical and hyperbolic surfaces. In the reference flow, the aplanatic point of the meniscus associated with the point AI is aligned with the lens focus, the Controlled part is set so that the focus F2 of its elliptical surface is aligned in the workflow with the focus of the lens, and the focus PI of the beam-splitting cube matches the point AI . The diaphragm is observed to observe the interference pattern of the reference and working streams. The shape of the surface is judged by the curvature of the observed interference fringes. 4 il. cl

Description

The invention relates to a measurement technique and can be used in monitoring optical components with elliptical and hyperbolic surfaces.

An interferometer is known for controlling the shape of second-order aspherical surfaces. In a known interferometer, a spherical reflector is installed in the working stream, the center of curvature of which is aligned with one of the foci of the test surface. The reflector together with the controlled surface form an aberration-free system.

The closest in technical essence to the achieved effect to the proposed device is an immersion interferometer containing successively installed laser, lens and a beam-splitting cube that divides radiation into two streams. Reflective elements with

spherical surfaces. The device for observing the interference pattern is located behind the beam-splitting cube in the autocollimation course of the rays.

The disadvantage of the prototype is a decrease in the accuracy of control due to errors introduced by the difference in the refractive indices of the immersion liquid and the reflector with a spherical surface. In addition, the measurement performance is reduced due to the need to place the test piece in a cuvette with an immersion liquid.

The purpose of the invention is to improve the accuracy and productivity of control of elliptic and hyperbolic surfaces.

This goal is achieved by improving the interferometer for controlling the surface shape, containing successively installed laser, lens, beam-splitting cube, and

SL

sl o

radiation on two streams, each of which has a reflective element, and an interference pattern observation system

Distinctive features of the interferometer are that it is equipped with an aplapatic meniscus installed in one of the streams so that one of its aplapatic points is aligned with the focus of the lens and the second beam-splitting cube located between the meniscus and the observation system The brighter faces of both cubes are perpendicular, and the reflective elements are made with flat reflective deflectors and are oriented at an angle to the direction of the corresponding flow.

Figure 1 is a diagram of an interferometer for controlling convex elliptical surfaces; figure 2 - to control concave elliptical surfaces; in FIG. 3, to control convex hyperbolic surfaces, in FIG. 4, to control concave hyperbolic surfaces.,

The interferometer circuits turn off the following elements: 1 laser 1, a beam-breaking cube 2, a mirror 3, a prism 4, a beam-splitting cube 5, a diaphragm 6, lenses 7-10, aplanatic menisci 11-14, and lenses 15-18. 22 with aspherical surfaces 23-26.

The interferometer (Fig. 1) is composed of a successively mounted laser 1, a lens 7 and a separating cube 2, which divides the radiation into two streams. Reflective elements are installed in each of the flows; they are made with flat reflecting surfaces oriented at an angle to the direction of the corresponding flow. One of the streams is a working one. In this stream, the reflective element is a mirror 3. In the other stream, which is the reference, the prism 4 is a reflective element. The interferometer is equipped with an aplanatic meniscus 11 installed in the reference stream so that one of its aplanati These points are aligned with the focal point of lens 7. Between meniscus 11 and the nobule system, including lens 15 and diaphragm 6, a second beam-splitting cube 5 is inserted. The beam-splitting faces of cubes 2 and 5 are perpendicular to each other.

The interferometer (figure 1) is designed to control the shape of the convex elliptical surface 23 of the optical part 10. The focus of the lens 7 in the working stream is aligned with the focus F2 of the elliptical surface 23. Aplanatic point t meniscus 11

match cube 5 with the focus of the FI surface 23. The conjugate points AI and FI with the lens 15 are projected into the center of the diaphragm 6.

In the interferometer (Fig. 2), lens 8 focuses laser radiation into the F2 focus of the concave elliptical surface 24 of the optical part 20. A meniscus 14 is guided into the reference flux, whose aplanatic AI point with beam-splitting cube 5 is matched with the FI focus of the controlled surface 24. Conjugate AI and the FI lens 16 projects into the center of the diaphragm 6.

In the control (Fig. 3) of the convex hyperbolic surface 25 of the optical part 21, the objective 9 focuses the radiation into the focus F2 of the surface 25. The aplanatic point AI of the meniscus 13 by dice 5 matches the focus of the surface 25. The points AI and FI are designed in center aperture 6.

Lens 10 (FIG. 4) focuses the radiation into the focus Fa of the concave hyperbolic surface 26 of the optical part 22. In the reference flux of the interferometer, there is a meniscus 14, one of the aplanatic points of which is aligned with the focus FI of the surface 26, and the other aplanatic point is conjugated cube 5 with focus FI of surface 26 is projected by lens 18 into center of diaphragm 6.

In the considered schemes, after laser 1, a beam expander (not shown) can be installed along the rays.

The interferometer (figure 1) works as follows.

A parallel beam of radiation coming out of laser 1 is converted into convergent lens 7, and the beam-splitting cube 2 divides the beams into reference and working streams. In the reference stream, the aplanatic point of the meniscus 11, conjugated with the point AI, is aligned with the focus of the lens 7. Controlled part 19 is set so that the focus F2 of its elliptical surface 23 is aligned in the workflow with the focus of the lens 7, and the focus FI by the beam-splitting cube 5 was aligned with the AL point. The eye located behind the diaphragm 6 observes the pattern of interference of the reference and working flows. The working flow is reflected from the elliptical surface under control. The shape of the surface is controlled by the curvature observable interference bands.

The operation of the interferometers shown in FIGS. 2-4 is similar to that described.

The use of an interferometer is advisable to control smallOblritic (for example, with a diameter up to mm) optical components with elliptical and hyperbolic surfaces. Compared with the prototype, the interferometer is simpler, since there is no cuvette with an immersion liquid to place the reflecting element and the part being monitored. The absence of an immersion liquid improves the control performance, since the operation of filling the cuvette with an immersion liquid is eliminated, and the accuracy of control is exceeded, since Errors introduced by the difference in the refractive indices of the immersion liquid and the reflection element are eliminated.

Claims (1)

The claims, t Interferometer for controlling the surface shape, containing a lens and a sequentially installed laser, a light-dividing cube dividing the radiation by 0 five 0 two streams, each of which has a reflective element, and an interference pattern observation system, characterized in that, in order to improve the accuracy and performance of monitoring parabolic surfaces, the lens is installed in one of the streams, the interferometer is equipped with an aplanatic meniscus and a second beam-splitting cube, the meniscus is installed in the same flow as the lens, so that one of its aplanatic points is aligned with the focus of the lens, and the second beam-splitting cube is located between the meniscus and the system on Luden so that beamsplitting cube faces both perpendicular and reflective elements are reflective flat surfaces and oriented at an angle to the direction of the respective stream. 6 Fig.Z