RU1835047C - Holographic interferometer - Google Patents

Abstract

FIELD OF THE INVENTION This invention relates to a measurement and control technique, primarily to holographic interference devices for controlling the shape of surfaces of optical parts. The invention solves the problem of controlling large optical surfaces i improving the accuracy of control. A beam splitter is installed along the radiation, designed to separate the radiation into reference and subject channels, two mirrors, with the possibility of rotation, and a spatial filter. Perform a beam splitter N-channel. for example, in the form of an N-faceted lyramide and set at its apex with respect to the radiation source. The interferometer is equipped with a lens. N-2 additional holograms of the reference surface. N-1 additional mirrors, N-2 additional spatial filters and one of the additional mirrors are placed in the object beam with the possibility of rotation around the axis. perpendicular to the beam axis. a N-2 additional mirrors and additional spatial filters are arranged in pairs along the radiation of N-2 channels divided by the beam splitter, and N-1 holograms of the reference surface are placed in a common holder along the radiation along a lens made common to N -1 subject channels, about the intersection of subject channels with the controversial. When controlling the shape of optical surfaces with a diameter of 1000-3000 mm. This embodiment provides high accuracy control with a root mean square error of the wavefront estimate from each zone during computer processing (a 0.02A). 3 ill.

Description

The invention relates to a measurement and control technique, primarily to holographic interference devices for controlling the surface shape of optical parts.

The known device operates as follows.

The radiation from laser 1 is divided by beam splitter 2 into two channels: subject and

supporting. In the object channel, the light beam passes through a spatial filter 3, which forms a diverging spherical wavefront, a beam splitter plate 4, located at an angle to the optical axis. From the beam splitter plate 4, light is incident on the workpiece 5. is reflected from it to the beam splitter plate 4 and falls on the holographic plate mounted in the holder 6.

8

2

Xi

 with

In the reference canapes, light is incident on a rotary mirror 7, a spatial filter Q, a collimator lens 9, which creates a flat wavefront, and on a rotary mirror 10, which directs the wavefront to a topographic plate.

The topographic plate contains a record of the reference wavefront from the Billet in the initial state. The light from the reference channel incident on the hologram restores the comparison wavefront that interferes with the diverging spherical wavefront coming from the workpiece. The resulting interference pattern shows the difference between the preform and its initial state.

The well-known holographic interferometer can only be used to control a workpiece with a diameter of up to 700 mm.

The disadvantage of the prototype device is the inability to control large optical surfaces with a diameter of 1000-3000 mm and the low accuracy of the control due to the low energy efficiency of the circuit, namely: a hologram is recorded for a diverging beam in the object channel, and this uses a small part of the light flux. reflected from the workpiece m limited by the size of both the beam splitting and the splitting plates,

The purpose of the invention is to enable control of large optical surfaces and to increase the accuracy of control.

This goal is achieved by the fact that in a holographic interferometer to control the shape of the optical surface containing a source of coherent radiation, a beam splitter installed along the radiation, designed to separate the radiation into the reference and subject channels located sequentially along the radiation. the reference channel, two mirrors mounted for rotation, and a spatial filter located in the object beam, a spatial filter and a hologram of the reference surface, the beam splitter is made N-channel, for example, in the form of an N-faced pyramid and is mounted with an apex relative to the radiation source, the interferometer is equipped lens, N-2 additional holograms of the reference surface, N-1 additional mirrors, N-2 additional spatial filters, one of the additional mirrors is located in front of Tnom beam and pivotally mounted

around the axis perpendicular to the beam axis, N-2 additional mirrors and additional spatial filters are arranged in pairs along the radiation of N-2 channels separated by the beam splitter. N-1 holograms of the reference surface are placed in a common holder and located along the radiation behind the lens, made common for N-1 subject channels, in place

0 intersection of subject channels with reference.

The implementation of the beam splitter in the form of a pyramid pyramid allows you to divide the radiation into five light beams, one of

5 of which fall into the reference channel formed by known elements, and four of them are subject, formed by both new and known elements.

0 Light beams passing through 4 subject channels are incident on 4 zones of a controlled surface, which allows obtaining information from a large diameter surface.

5 Although by themselves, new structural elements are known from the prior art and perform well-known functions, their relative position allows obtaining information from four zones of controlled

0 surface at a time.

Thus, the introduction of three additional holographic plates, which are known per se, allows obtaining information on a large-diameter surface from

5 1000-3000 mm, without increasing the size of the plates, but only increasing their number.

The relationship between the diameter of the surface to be monitored DI and the diameter of the lens D2 can be represented by the mathematical expression D.I.

The lens diameter Da affects the accuracy of the control. When the diameter of the lens DI is used, the light flux reflected from the surface being monitored is not used to the full extent, therefore the energy efficiency of the circuit decreases, which leads to a decrease in the accuracy of the control.

With the diameter of the lens

0 DI, the angle of incidence of the central beam in each subject channel will be more than 15 °, which also leads to a decrease in the control accuracy.

Only with lens diameter

5 DI, the luminous flux incident on the controlled surface will be maximum, and the angle of incidence of the central beam in each object channel on the controlled surface should not exceed 15 °.

Thanks to the interaction of all the features, the claimed combination of features has developed a new technical property, different with respect to the prototype, and expressed in the ability to control the shape of optical surfaces with a diameter of 1000-3000 mm. In addition, the accuracy of control has been improved, which is an enhanced property with respect to the prototype.

Figure 1 shows the optical diagram of the proposed device; figure 2 presents the optical circuit of the device is an analogue (Common circuit); Fig. 3 shows an optical diagram of a prototype device.

The holographic interferometer for controlling the shape of the surface contains a coherent radiation source 1 (laser), a beam splitter 2, made in the form of a pyramid pyramid, mounted vertically to the radiation source 1, and designed to separate the radiation into 5 light beams, one of which is a reference and four - subject.

In each of the subject channels, 3,4,5,6 rotary mirrors and spatial filters, 8, 9. 10 are installed sequentially (forming diverging spherical wave fronts, incident at an angle on A of the zone of the surface under control).

In the reference channel, rotary mirrors 11, 12 and a spatial filter 13 are sequentially installed.

A lens 15, the diameter of which is 2/3 of the diameter of the surface 14 (D2 2/3 DI}, is mounted in such a way that it focuses 4 spherical wave flows reflected from the four zones of the surface 14

A holder 16 for holographic plates for recording the wavefront from the reference surface is mounted near the focus plane P of the subject wave fronts (before or after it).

The device operates as follows.

The light from the source of coherent radiation 1 enters the beam splitter 2 and is divided into 5 beam-channels in it, one of which is reference and 4 are subject. In four object channels, the light is rotated by rotary mirrors 3, 4, 5, 6, and spatial filters 7, 8, 9, 10 form 4 diverging spherical wave fronts that fall at an angle of 10-15 ° to the controlled surface 14 by 4 e e zones.

Reflected from the controlled surface 14, four wave spherical fronts are focused by the lens 15 in the plane P.

In the reference channel, the light flux is rotated by the mirrors 11, 12, and the spatial filter 13 forms a diverging spherical wavefront, which, incident at an angle of 20 ° on the holographic plates mounted on the holder 16, restores the reference wavefronts from four zones of the reference surface 17, which were obtained from it previously and in the same pattern, moreover, the reference surface 17 was in place of the controlled surface 14.

As a result, 4 reference wavefronts reconstructed from holograms recorded in the same pattern from a reference surface 17 interfere with wavefronts from four zones of the controlled surface 14.

The interference pattern is evaluated either visually or recorded on photographic material. Mathematical processing of interference patterns can be performed using one of the interferogram processing programs obtained in the Fizeau scheme.

Instead of holograms recorded for reference surface 17, computer generated holograms can be used.

The proposed technical solution can be used to control the shape of optical surfaces with a diameter of 1000-3000 mm, and the prototype device only for surfaces of 700 mm.

At the same time, it provides high accuracy of control; the root-mean-square error of the wavefront estimation from each zone during computer processing is 02A.

Claims (1)

The claims A holographic interferometer for controlling the shape of the optical surface, containing a coherent radiation source installed along the radiation, a beam splitter designed to separate the radiation into the reference and subject channels located in series along the radiation in the reference channel, two mirrors mounted for rotation, and a spatial filter located in the object beam, a spatial filter and a hologram of the reference surface, characterized in that the beam splitter is made in the form of an IM-graph of the pyramid and is set at the top with respect to the radiation source, the interferometer is equipped with a lens, N-2 additional holograms of the reference surface, N-1 additional mirrors. N-2 additional spatial filters, one of the additional mirrors is located in the object beam and is installed with the possibility of rotation around the axis perpendicular to the axis of the beam, N-2 additional mirrors and additional relative spatial filters are arranged in pairs along the radiation of N-2 channels separated by the beam splitter. N-1 holograms of the reference surface are placed in a common holder and located along the radiation behind the lens, made common for N-1 subject channels, at the intersection of the subject channels with the reference . M17) rie. 1 AT Ф4 / &. 2