JPS6023281B2 - Interferometer for inspecting the shape of the convex surface of optical elements - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical element inspection apparatus, and more particularly to an interferometer for inspecting the shape of a spherical surface of an optical element.

Antecedents of the Invention Interferometers for testing the shape of the convex spherical surface of a closing lens for the use of test glasses and compensators (spherical compensators) are well known in the art (SoDersl.B., 1. Re
s. Nat. Bm. Stan ship rd. ,19 pay,53,
M. 1, p. 29).

Since the diameter of the test glass is generally smaller than the diameter of the surface to be inspected, it is impossible to inspect the surface to be inspected by passing light through the test glass only once, and it is impossible to repeatedly apply the test glass to the surface to be inspected. waste a lot of time. In addition, in order to bring the test glass into contact with the surface to be inspected for inspection, the surface to be inspected must be examined with great care. If the radius of the surface to be inspected is changed due to manufacturing reasons, a new test glass must be made, which increases the cost of the inspection operation. Interferometers that use compensators to transform a plane or spherical wavefront into a wavefront of a desired shape are well known in the art (G.V. Kre
opalova, D. T. Pmyaev, Studie
s and Check-up of Optical
Satems, M. Mashi DishstrMniePub
l. , 1978).

The problem with testing with such interferometers is that information about errors in the surface to be tested is obtained simultaneously from the entire swath of the surface to be tested, rather than from individual areas of the surface. - This problem is solved by using a compensator designed to direct the light in the same concentrated light east shape with the apex coinciding with the center of the convex spherical surface to be inspected. If a convex spherical surface is applied to the lens, the compensator also takes account of the effects of other surfaces on the lens, so that the convex surface can be inspected in the same way as a concave surface, where the surface is inspected from its center of curvature. must be designed with this in mind. To implement this method, multiple compensators must be used individually. This is because each compensator can only be used to test one lens with a given shape. If the surface to be inspected is the surface of an optical element made of opaque material, an interferometer based on the use of a compensator is suitable for inspection of convex surfaces using a light beam that penetrates inside the material of the optical element. , cannot be used at all. In the art, an interferometer designed for inspecting the shape of a convex spherical surface of an optical element is known, which consists of a monochromatic light source and a light beam located behind it in a light path. , these devices consist of a matching lens, a light splitter, a compensator, a lens system having as its downstream surface a reference concave spherical surface whose center of curvature is optically aligned with the rear focus of the matching lens; Interferometers that include a recording system for recording interference patterns are well known (YuV.: Kulomiybov,
lntehe-rometedai. , MasinosV
oenie Publ. , 1976 p296).

This interferometer has a relatively small diameter (loo to 15
It is possible to inspect the spherical surface of an optical element having a certain value of the ratio ○/R, where D and R are the diameter and radius of the surface to be inspected, respectively.

Prior art interferometers are of limited use when examining convex spherical surfaces with large diameters (on the order of 500 to 60 mm) and other values of D/R ratios. The reason for this is that the lens system must be replaced with a reference surface, arduous adjustment work is required, and the interferometers of this conventional technique are unduly large in size. DISCLOSURE OF THE INVENTION The present invention is based on the problem of providing an interferometer for inspecting the shape of a convex surface of an optical element. Approximately 60 ships)
High-precision inspection of surfaces of small diameter (approximately 10 W) is possible without the need for laborious adjustment work, and the interferometer is relatively small in size.

This problem involves an interferometer for inspecting the shape of the convex surface of an optical element, which consists of a monochromatic light source and a series of devices placed behind it during the Koto pilgrimage. A lens, a light splitter, a compensator, a lens system having as its last surface a reference concave spherical surface whose center of curvature is optically aligned with the rear focal point of the focusing lens by the compensator, and this reference surface. In such an interferometer including a recording system for recording an interference pattern obtained by reflection of a light beam from This series includes additional compensators, additional light splitters,
An additional focusing lens, a lens system which also has a reference concave spherical surface with a radius of curvature different from that of the last reference surface, adds a rear focal point from the monochromatic light source to the first center of curvature in the optical path. A mirror system for directing light from a monochromatic light source to an additional matching lens optically aligned by a compensator, and an interference pattern obtained by reflection of the light from an initial reference plane of the lens system. The solution is to include an additional recording system for recording.

In such an interferometer, the lens system is preferably composed of two positive niscus lenses and two plano-convex lenses disposed between these meniscus lenses and having a plane facing the convex surface of the final niscus lens.

For testing convex spherical surfaces with a small D/R ratio, the lens system preferably consists of two positive varnish lenses and a biconvex lens placed between these lenses.

To test convex spherical surfaces with large D/R ratios, the lens system consists of two positive niscus lenses, and the convex surface of at least one lens is aspheric and functions as a main compensator and an additional compensator. It is preferable to do so.

According to the interferometer of the present invention, it is possible to inspect the convex spherical surface of an optical element having a large diameter, in which the maximum value of the D/R ratio is in two ranges, and this inspection does not require changing the design of the interferometer. Additional assembly adjustments or different values of D
This is performed without replacing parts when testing an element having a /R ratio.

All parts of the interferometer are stationary and form a compact optical assembly that can be conveniently placed on an optical bench, yet can be formed as a separate unit for transportation.

In the interferometer of the present invention, switching from one numerical range of the D/R ratio of the surface to be inspected to another can be accomplished simply by rearranging the mirror system that directs the light beam to the additional lens. hand,
There is no need to add or adjust an interferometer. In the interferometer optical system, simultaneously using two reference concave spherical surfaces with different D/R ratios means using two interferometers with the same reference surface, or using the same reference surface. It is much more economical to build than using prior art interferometers that use two interchangeable lenses with .

The invention will now be described with reference to specific embodiments of the invention that are illustrated in the accompanying drawings. FIG. 1 is an optical diagram of the interferometer showing the optical path for testing a convex spherical surface for one range of D/R ratios.

FIG. 2 is the same view as shown in FIG. 1, and shows the passage of the light east for Yangsha, which inspects convex spherical surfaces for different ranges of D/R ratios.

FIG. 3 shows an embodiment of a lens system adopted for the inspection of convex spherical surfaces with a small D/R ratio.

FIG. 4 shows an embodiment of a lens system suitable for inspecting convex spherical surfaces with a large D/R ratio. Embodiments of the Invention The interferometer according to the invention comprises a monochromatic light source 1 (FIG. 1), such as a helium-neon laser, a rotating plane mirror 2 capable of occupying a position pupil 1 and a microscope having a telecentric light beam. It includes a matching lens 3 like an objective lens.

The combining lens 3 receives the light emitted from the light source 1 and reflected by the mirror 2, and forms a point light source directly at the rear focal point F of the lens 3. The light splitter 4 is, for example, a cube with a translucent surface arranged in the optical path behind the lens 3, and Koto uses this cube to divide the compensator 5 into a compensator 5 consisting of a single lens or a group of lenses. deflected in the direction of

The optical axis of the compensator 5 is aligned with the optical axis of the lens 3 by a light splitter.

A lens system 6 consisting of lenses 7, 8, 9 and 10 is arranged behind the compensator 5 along its optical axis. The last surface A of the lens system 6 is a reference concave spherical surface, and this reference concave spherical surface A has its center of curvature adjusted to the rear focal point F of the lens 3 by the compensator 5
, are optically matched to. The first surface B of the lens system 6 is also a reference concave spherical surface, but its radius of curvature is generally different from that of the surface A. A recording system 11 is arranged behind the light splitter 4 along the optical axis of the lens system 6 and the compensator 5 in order to record the interference pattern obtained by reflection from the surface during the inspection.

As shown in FIG. 1, the recording system consists of a photographic lens 12 and a photosensitive layer 13. The optical element 14 to be inspected is placed behind the lens system 6 in the optical path, as shown in FIG.

The surface 15 of the device to be tested is arranged so that the center of curvature of this surface coincides with the center of curvature of the reference surface A. Additional compensator 16
An additional light splitter 17 and an additional light splitter 17 are arranged behind the lens system 6 along its optical axis to align the optical axis of this compensator with the optical axis of the additional focusing lens 18. The rear focal point F2 of the lens 18 is aligned with the center of curvature of the reference concave spherical surface B of the lens system 6 by the compensator 16. An additional system 19 is arranged along the optical axis of the lens system 6 behind the light splitter 17 for recording the interference pattern bounded by the reflection of the light from the reference concave spherical surface B during the inspection.

In addition, a stationary plane mirror 20 (or group of mirrors) is provided to direct the light beam to the lens 18, and this stationary plane mirror 2
0, in combination with the rotating mirror 2, forms a system of mirrors for directing the light from the light source 1 to an additional focusing lens 18. FIG. 2 shows an optical diagram of the same interferometer as shown in FIG. 1, the only difference being that optical element 21 is replaced by compensator 5 and lens system 6.
Moreover, the surface 22 to be inspected of the element 21 is placed so that the center of curvature of this surface 22 coincides with the center of curvature of surface B.

Figures 1 and 2 show two positive varnish lenses 7 and 1.
0 and two plano-convex lenses 8 and 9 arranged between them.

The convex surfaces of lenses 7 and 10 are opposite the planes of lenses 8 and 9. FIG. 3 shows an embodiment of a lens system 6', which includes two convex meniscus lenses 23 and 2.
4 and a biconvex lens 25 disposed between both of these meniscus lenses.

Both concave surfaces A and B of lenses 24 and 23 are reference spherical surfaces. FIG. 4 shows an embodiment of the lens system 6'', which consists of two positive niscus lenses 26 and 27 having reference concave spherical surfaces B and A, respectively. At least one of the convex spherical surfaces 28 and 29 One, in this embodiment 28, is an aspherical surface which, in combination with the spherical surface 29, serves as the main compensator 5 (FIG. 1) and the additional compensator 16, i.e. The compensators 5 and 16 are removed, and the lens system 6'' (Fig.
(shown in FIG. 2). The optical alignment of the rear focal point F, of lens 3 with the center of curvature of surface A and the optical alignment of the rear focal point F2 of lens 18 with the center of curvature of surface B is determined by the specific shape of surfaces 29 and 28. This is ensured by granting. The operating mode of the interferometer according to the present invention will be described as follows. The shape of the convex spherical surface of the optical element is R
It is possible to test in two different numerical ranges of /○ ratio.

To perform an inspection in one range of R/D ratios, plane mirror 2 (FIG. 1) is set at position 1.

The light emitted from the light source 1 reaches a plane mirror 2, and is directed to a matching lens 3 by this plane mirror. The light east passage is indicated by an arrow in FIG. The light that has passed successively through the light splitter 4, the compensator 5, and the lenses 7, 8, 9, and 10 enters the reference plane A at right angles, one part of which is reflected by the reference plane A, and one part of which is reflected by the reference plane A. passes through the same reference plane A to the surface to be inspected 1
5. The light beam reflected from the surface A and the light beam reflected from the surface 15 interfere with each other to produce an interference pattern, and this interference pattern is recorded by the recording system 11. The subsequent processing of the interference pattern showing toxicity≦ with respect to the shape of the surface to be inspected 15 is carried out according to a conventional method, which is not disclosed herein. To carry out inspections in other ranges of R/D ratios, the plane mirror 2 (FIG. 2) is normally set to position 0'. Light exits the monochromatic light source and is reflected from the mirror 20,
The light reaches an additional light beam 18, passes through an additional light splitter 17, an additional compensator 16 and lenses 10 to 7 one after another, and then enters the reference plane B at right angles. The light beam reflected from the surface B and the light beam reflected from the surface 22 of the device to be inspected 21 interfere with each other to produce an interference pattern, and this interference pattern is recorded by the additional recording system 19. The reference concave surfaces A and B belonging to lenses 10 and 7 (FIGS. 1 and 2), respectively, have approximately the same diameter, but their radii of curvature are considerably different, with a ratio of radii of curvature of approximately 1:2. It is 5.

This makes it possible to use surfaces A and B to inspect convex spherical surfaces with different R/○ ratios.
Lens system 6 (Figures 1 and 2) has a D/R ratio of 0.2.
Two R/D ratio ranges within the range from 0.6 to 0.6 are reasonable for use in testing convex spherical surfaces. For inspection of convex spherical surfaces with large D/R ratios of the order of 0.7 and above, it is preferable to use the lens system 6^ shown in FIG. 4. D/R on the order of 0.05 and below
To inspect a convex spherical surface with a ratio, a lens system 6 shown in Fig. 3 is used.
′ is preferably used.

The use of the interferometer with lens system 6' (Fig. 3) or the use of the interferometer with lens system 6^ (Fig. 4) is similar to that shown in Figs. It is similar to the usage of meter.

The lens systems 6, 6' and 6r shown in FIGS. 1 to 4 are all composed of independent optical elements, and the diameters of these elements do not practically exceed the diameter of the surface to be inspected, and the thickness of the lenses The total thickness including the air gaps between the lenses is much smaller than the diameter of the lens system.

Since the interferometer assemblies other than the lens system are much more compact than the lens system, it is possible to quickly set up the interferometer on an optical bench. According to the interferometer embodiment shown in FIGS. 1 and 2, there are two interferometers having a diameter of up to 60 mm and a D/R ratio range centered on about 0.6 and about 2.4. It is possible to inspect convex spherical surfaces in the area.

The optical system of this interferometer can form a spherical wavefront directed toward the reference planes A and B, and the deviation of this wavefront from the spherical surface is at most equal to It's nothing more than that. There is no difficulty in manufacturing the precise reference concave spherical surfaces A and B of the lens system, and therefore the inspection accuracy is ^/
10L, and if the error inherent in the reference spherical surface is taken into consideration, the accuracy is good at over 1/20. Using this interferometer, it is possible to inspect the most frequently used wide-angle, long-bridge objective lenses. Industrial Application The interferometer of the present invention is used for inspecting the shape of a convex spherical surface of a large-diameter optical element, such as a wide-angle, long-angle photography objective lens.

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Claims (1)

[Scope of Claims] 1. An interferometer for inspecting the shape of a convex surface of an optical element, which consists of a monochromatic light source and a series of devices arranged behind it in the path of a light beam. focusing lens,
a light splitter, a compensator, a lens system having as its last surface a reference concave spherical surface with a center of curvature optically aligned by the compensator with the rear focus of the focusing lens; and this reference surface. In an interferometer including a recording system for recording an interference pattern obtained by reflection of a beam from an additional compensator 16, an additional light splitter 17, an additional focusing lens 18, a lens system 6 closest to the monochromatic light source 1 which is also a reference concave spherical surface with a radius of curvature different from that of the reference surface A; A mirror system 20, 2 for directing the light beam from the monochromatic light source 1 to an additional focusing lens 18 whose rear focal point F_2 is optically aligned by an additional compensator 16 to the center of curvature of the first surface. and an additional recording system 19 for recording an interference pattern obtained by reflection of the light beam from the reference surface B of the lens system 6. 2 Lens system 6 includes two additional meniscus lenses 7,1
0 and two plano-convex lenses arranged between these lenses and having a plane opposite to the convex surfaces of the meniscus lenses 7 and 10, the shape of the optical element according to claim 1. interferometer for testing. 3 The lens system 6' includes two positive meniscus lenses 23, 2
4. An interferometer for inspecting the shape of a convex surface of an optical element according to claim 1, characterized in that the interferometer comprises a double convex lens 25 disposed between these lenses. 4 Lens system 6″ consists of two positive meniscus lenses 26,2
7 and at least one convex surface 2 of these lenses
8 is an aspherical surface, and main and additional compensators 5, 1
6. An interferometer for inspecting the shape of a convex surface of an optical element according to claim 1, characterized in that the interferometer functions as an interferometer for inspecting the shape of a convex surface of an optical element.