RU2255307C1 - An interferometer for controlling of the form of prominent, concave spherical and flat surfaces of large-sized optical components - Google Patents

Abstract

FIELD: measuring instruments.

SUBSTANCE: the interferometer for controlling of the form of prominent, concave spherical and flat surfaces of large-sized optical components has a source of monochromatic radiation, a collimator and an objective, one after another located a beam divider, a flat mirror and an aplanatic meniscus with a reference surface and also an observation branch located behind the beam divider in beam return and a working branch consisting out of a spherical mirror with a compensator which form a focusing system. Depending of the form of a controlled surface focusing of the working branch of the interferometer is executed at replacing the compensator and the basic block of the interferometer which has an illuminating branch. A beam divider, a flat mirror, an aplanatic meniscus and an observation branch relative to a fully stabilized spherical mirror along an optical axis on such a distance at which the beams reflected from the spherical mirror fall on the controlled surface transversely to its surface.

EFFECT: expansion of nomenclature of controlled surfaces, decreasing large-sized dimensions of the interferometer.

2 cl, 3 dwg

Description

The invention relates to measuring technique, namely to interferometry, and can be used to control the shape of large concave, convex spherical and flat surfaces.

A known interferometer for controlling the surface shape of convex spherical surfaces of large-diameter lenses (USSR Author's Certificate No. 4448347, class G 01 B 9/02, 1972), comprising a laser light source, arranged in series with a telescopic system, a beam splitter, a lens, a compensator, a reference spherical mirror , recorder interference pattern.

The disadvantage of the interferometer is the relatively large overall dimensions of the reference surface of the mirror and the ability to control only convex spherical surfaces of a limited range.

Closest to the invention in technical essence is an interferometer for controlling the shape of the spherical surfaces of lenses (USSR Author's Certificate No. 1068699, class G 01 B 9/02, 1984), containing a monochromatic light source, a quarter-wave phase plate, a telescopic system, a lens and a lens forming a lighting branch, a compensator, and a reference spherical mirror forming a working branch and an observing system.

The disadvantage of the interferometer is its complexity, the need to use in each specific case the control of a special compensator and the replacement of optical components in the working branch of the interferometer, the inability to control flat optical surfaces.

The problem to which the invention is directed, is to expand the range of controlled surfaces of both spherical convex and concave, and flat surfaces, reducing the overall dimensions of the interferometer.

The technical result that is achieved as a result of solving this problem is to increase control performance and accuracy.

The specified technical result is achieved due to the tunable focusing system of the working branch of the interferometer, into which a large-sized spherical mirror and a lens compensator are introduced as a focusing system. An interferometer for controlling the shape of convex, concave spherical and flat surfaces of large-sized optical parts contains an illuminating branch consisting of a monochromatic radiation source, a collimator and a lens, a beam splitter in series, a flat mirror and an aplanatic meniscus with a reference surface, as well as an observation branch located behind the beam splitter in reverse ray path, and a working branch, consisting of a spherical mirror with a compensator, which form a focusing system. To change the focus of the working branch of the interferometer, it is necessary to mutually move the compensator and the base unit of the interferometer, consisting of a light branch, a beam splitter, a flat mirror, an aplanatic meniscus, and an observation branch, relative to a stationary spherical mirror along the optical axis at such distances at which the rays reflected from spherical mirrors fall on the controlled parts perpendicular to their surfaces regardless of the shape of the controlled surface.

The drawing shows optical circuits of an interferometer for monitoring large-sized optical parts of concave (1a), convex (1b) spherical and flat (1c) surfaces.

The interferometer contains a lighting branch 1, consisting of a monochromatic radiation source, a telescopic system and a lens, a sequential beam splitter 2, a flat mirror 3, an aplanatic meniscus 4 with a reference surface, a focusing system for the working branch of the interferometer, consisting of a compensator 5 and (6) and a large-sized mirror 7, the controlled surface 8 and the observation branch 9.

The interferometer operates as follows.

The rays of light formed by the illuminating branch 1 pass through a beam splitter 2, a flat mirror 3, fall on the reference surface of the aplanatic meniscus 4, facing the working branch of the interferometer, partially reflected from the reference surface and create a reference wavefront of comparison. The other part of the rays passes through the reference surface, the compensator 5 and (6), the large-sized mirror 7 and falls along the normal to the controlled surface 8, is reflected from the controlled surface, forming a working wavefront of comparison. Then the radiation passes through the working branch of the interferometer in the opposite direction and interferes with the reference wavefront. The beam splitter 2 deflects light rays reflected from the reference surface 4 and the controlled surface 8 into the observation branch 9. To expand the range of controlled parts, a large-sized spherical mirror 7 and a lens compensator 5 and (6) are introduced as a focusing system in the interferometer working branch. This allows you to control both spherical convex and concave, and flat surfaces, use the reference and auxiliary optical elements of a much smaller light diameter than the surface to be controlled, and limit the length of the subject branch, which is associated with the laser coherence length and the requirement of vibration protection of the interferometer circuit.

In the above schemes, the focusing of the working branch is rearranged by mutual movement of the base unit and the compensator along the optical axis of a stationary spherical mirror. The calculated distances between the base unit, the compensator and the spherical mirror are shown in the drawing. In this case, the magnitude of the spherical aberration of the wave front formed by large-sized mirrors will be significant. To compensate for the spherical aberration of the mirror, two lens compensators are designed. When calculating the compensators, we used the method of compensating aberrations of surface normals (Puryaev D.T. Methods of control of optical aspherical surfaces. M .: Mashinostroenie, 1976).

In this case, all the rays fall on a controlled surface perpendicular to its surface. A compensator with a spherical mirror ensures such a path of rays that the real wavefront is again accurately converted with a permissible error into a spherical or flat wavefront.

The designs of the calculated lens compensators are quite simple. To control concave and convex surfaces, the calculated lens compensator is a two-component glued element 5. To control flat surfaces, the aforementioned compensator with an additional two-component glued element is used 6. The manufacture of a spherical mirror does not cause significant difficulties.

Computational experiments have shown that the proposed interferometer schemes allow you to control:

convex spherical surfaces with a radius of curvature from 1500 mm to 4400 mm (with a relative aperture A = 1: 8 to A = 1: 16), the maximum residual aberration of the working branch of the interferometer λ / 48;

concave spherical surfaces with a radius of 11,000 mm to 17,000 mm (with a relative aperture A = 1: 11 to A = 1: 44), the maximum residual aberration of the working branch of the interferometer λ / 74;

flat surfaces with a diameter of 250 mm to 1000 mm, the maximum residual aberration of the working branch of the interferometer λ / 124;

Claims (2)

1. An interferometer for controlling the shape of convex, concave spherical and flat surfaces of large-sized optical parts, comprising a monochromatic light source, a telescopic system and a lens forming a lighting branch, as well as a beam splitter, a reference surface, a compensator, a controlled surface and an observation branch, which is installed behind the beam splitter in the reverse ray path, characterized in that a flat mirror is additionally introduced into the interferometer, changing the direction the optical axis and installed after the beam splitter, an aplanatic meniscus with a reference surface facing the compensator, made with the possibility of movement, a large, fixed stationary spherical mirror, a controlled part is installed sequentially behind it, while the light branch, beam splitter, flat mirror, aplanatic meniscus with a reference surface and an observing branch form the base unit, made with the possibility of mutual movement of it and the compensator along optical axis, relative to a large-sized spherical mirror at such distances at which the rays reflected from the large-sized spherical mirror fall on the controlled surface perpendicularly. 2. The interferometer according to claim 1, characterized in that when monitoring a flat surface, a second compensator is inserted into it, mounted behind the first compensator at a distance at which the rays reflected from the spherical mirror fall perpendicular to the controlled flat surface.