JPH05340839A - Simple interferometer - Google Patents

Abstract

PURPOSE:To obtain a simple interferometer which has a small number of parts, can be perform measurement accurately, and is used for inspecting and measuring an optical lens which is manufactured and assembled by a factory line, etc. CONSTITUTION:The title interferometer measuring the wave front aberration of a coherent incidence wave front 1 is provided with a cube beam splitter 3 and a reflection-type space filter 7 which is laid out on one surface of the cube beam splitter 3. Further, the mirror image of the space filter 7 according to the space filter 7 or the cube beam splitter 3 is provided at the curvature center with a spherical surface lens 2 which is adhered to the cube beam splitter 3, an image pick-up element 11 for converting interference fringes to electrical signal, and an image-forming lens 10 for forming an object to be inspected on the image pick-up element 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a simple interferometer used for inspecting and measuring the surface shape of an optical lens manufactured in a factory line or the like, and for inspecting and measuring the aberration of an assembled optical lens. is there.

[0002]

2. Description of the Related Art An interferometer currently used for performing the above-described inspection measurement will be described with reference to the diagram showing the configuration of the interferometer shown in FIG. 20 is the first beam splitter,
Reference numeral 21 denotes a pinhole 21a which serves as a spatial filter, and two microscope objective lenses 2 facing each other with the pinhole 21a as a center.
Reference wave generators 1b and 21c, reference numerals 22 and 24 are reflecting mirrors, 23 is a second beam splitter, 25 is a wavefront transmission apparatus having two aberration-corrected microscope objective lenses 25a and 25b, and 26 is an image forming device. A lens, 27 is an image sensor, and 28 is a display device.

The function of the reference wave generator 21 will be described. The incident wavefront is generally a distorted wavefront containing wavefront aberrations. In order to obtain a plane wave that can be used as a reference wavefront from such an incident wavefront, one of the microscope objective lenses 21b in the reference wave generator 21 focuses the incident wavefront on the pinhole 21a. If the size of the pinhole 21a is appropriately selected, the aberration component of the incident liquid surface will be
It is possible to obtain a spherical wave having no aberration by being removed by the pinhole 21a. A reference plane wave can be obtained by converting the spherical wave with no aberration into a plane wave by the other microscope objective lens 21c with the aberration corrected.

In the case of inspection measurement, a part of the incident wave front is transmitted by the first beam splitter 20, and it becomes a reference plane wave shaped by the reference wave generator 21.
It is reflected by and advances to the second beam splitter 23. In addition, part of the incident wavefront is generated by the first beam splitter 20.
The reflected wavefront reaches the reflecting mirror 24 and is reflected again, and the two aberration-corrected microscope objective lenses 25
After passing through the wavefront transmission device 25 composed of a and 25b, the second
Part of the light is transmitted by the beam splitter 23. At this time,
The two wavefronts that overlap with the above-mentioned reference plane wave interfere with each other to form interference fringes, the imaging lens 26 images the interference fringes on the imaging element 27, and the interference fringe image is displayed on the screen of the display device 28. .

[0005]

By the way, the interferometer shown in FIG. 5 described above has a large-scale device, and also has a large number of parts necessary for constructing the device. In addition, the microscope objective lens used in the reference wave generator 21 and the wavefront transmitter 25 must be well corrected for aberrations, which makes it difficult to manufacture a small and inexpensive device. ..

The present invention has been made in view of the above circumstances, and an object thereof is to provide an interferometer that has a small number of parts and can easily measure a wavefront aberration.

[0007]

SUMMARY OF THE INVENTION The present invention is an interferometer for measuring the wavefront aberration of a coherent incident wavefront, in which the coherent wavefront is made incident and split into a first optical path and a second optical path. A cube beam splitter, a reflective spatial filter arranged on the surface of the first optical path of the cube beam splitter, the spatial filter, or a mirror image of the spatial filter by the cube beam splitter. Placed so that it has a center of curvature,
And, a spherical lens bonded to a surface on the first optical path of the cube beam splitter, or on a surface facing at least one of the surfaces on the second optical path,
It is characterized in that it has an observation means provided on the optical path from which the cube beam splitter is emitted.

The above-mentioned means can further improve the performance by the embodiments described below. That is, in order to be suitable for the case where the incident wavefront is a parallel incident wavefront, in the above-mentioned interferometer, an optical system for converting the parallel incident wavefront into a spherical wave is preliminarily provided in the spherical lens closely contacting the cube beam splitter. Further, in order to facilitate visual measurement of the amount of wavefront aberration, in the above-mentioned interferometer, the cube beam splitter is movable on the surface which becomes a mirror image of the reflection type spatial filter by the cube beam splitter. The structure has a glass hemispherical lens having a center of curvature. In this case, a glass spherical lens and a cylindrical glass body may be combined instead of the glass hemispherical lens.

[0009]

As described above, the present invention is an interferometer for measuring the wavefront aberration of a coherent incident wavefront, including a cube beam splitter and a reflection type spatial filter arranged on the surface of the cube beam splitter. , The spatial filter, or a spherical lens having a mirror image of the spatial filter by the cube beam splitter in the center of curvature, and in close contact with the cube beam splitter, an imaging element for converting interference fringes into an electrical signal, It is composed of an image forming lens for forming an image of the inspection object on the image pickup device.

First, the case where the incident wavefront is convergent light will be described. The incident wavefront is incident on the cube beam splitter so that it is focused on one face of the cube beam splitter. A reflection type spatial filter, that is, a pinhole portion, has a predetermined reflectance on the light collecting surface,
Pinholes that allow light to pass through are arranged at the other portions without light absorption or reflection. Therefore, a spherical wave with no aberration can be obtained as a reflected wave on this converging surface.

If the other surface of the cube beam splitter is coated with a reflective film having the same reflectance as that of the reflective spatial filter, all incident waves are reflected and interfere with the spherical wave. If this is guided to the image sensor through the imaging lens and interference fringes are formed on the image sensor, or if an eyepiece is placed instead of the imaging lens and observed with the naked eye, the wavefront aberration of the incident wavefront can be observed. it can.

By disposing a spherical lens having the focal point as the center of curvature on the surface of the cube beam splitter facing the incident wavefront, the incident wavefront will not be refracted by the surface of the cube beam splitter and aberration will be generated. Can be prevented. If the incident wavefront is not convergent light, a condenser lens whose aberration is corrected is placed in front of the incident side of the cube beam splitter, as in the case where the incident wavefront is convergent light. Can be observed.

[0013]

1 is a diagram showing the configuration of a first embodiment of a simple interferometer of the present invention. In FIG. 1, 1 is an incident wavefront, 2 is a spherical lens which is in close contact with the incident side surface of the cube beam splitter 3, 4 is a cemented surface of the cube beam splitter 3,
Reference numeral 5 denotes a reflecting surface facing the incident side surface of the cube beam splitter 3 to which the spherical lens 2 is in close contact.
7 is a pinhole that constitutes a reflection type spatial filter arranged on the other surface 8 of the cube beam splitter 3, 9 is a spherical lens that is in close contact with the exit side surface of the cube beam splitter 3, and 10 is an image A lens 11 is an image sensor. In this embodiment, the image forming lens 10 and the image pickup device 11 constitute an observation means.

The spherical lens 2 is made of the same glass material as the cube beam splitter 3, and the spherical lens 2 is
The focal point and the center of curvature coincide with each other. The spherical lens 9 is also made of the same glass material as that of the cube beam splitter 3, and the center of curvature of the spherical lens 9 is made to coincide with the pinhole 7 constituting the reflective spatial filter.

This embodiment is constructed as described above,
The incident wavefront 1 partially passes through the cemented surface 4 via the spherical lens 2 and is condensed on the reflecting surface 5. The reflecting surface 5 reflects the focused wavefront with a certain reflectance. Also, the spherical lens 2
Part of the incident wavefront 1 that has passed through is reflected by the joint surface 4 and is incident on the pinhole 7 that constitutes a reflective spatial filter. The reflected wave of the wavefront incident on the pinhole 7 that constitutes the reflective spatial filter becomes a spherical reference wavefront. The pinhole 7 and the condensing point P on the reflecting surface 5 that form the reflective spatial filter are mirror image positions with respect to the joint surface 4.

The spherical reference wave from the pinhole 7 constituting the reflection type spatial filter and the wavefront reflected by the reflecting surface 5 are:
It passes through the overlapping spherical lens 9 at the cemented surface 4 and goes out of the cube beam splitter 3. Then, the interference fringes representing the wavefront aberration of the incident wavefront are imaged on the image sensor 11 by the imaging lens 10.

In the above structure, the reflectance of the pinhole 7 constituting the reflection type spatial filter is made equal to the reflectance of the reflecting surface 5, so that the contrast of interference fringes is improved. If the converging point of the incident wavefront and the pinhole 7 are made to coincide with each other, interference fringes can be automatically obtained, and therefore alignment adjustment is extremely simple. Moreover, since the optical path lengths are the same, the interference fringes can be observed even with light from a light source with low coherence. The spherical lens 9 is not always necessary, but if for some reason an output light without aberration is desired, it must be equipped.

FIG. 2 is a diagram showing the configuration of a second embodiment of the simple interferometer of the present invention. The structure of the reflecting surface 5 of the cube beam splitter 3 is different between the second embodiment and the first embodiment.
In the second embodiment, instead of coating the reflective surface 5 with a reflective film, the hemispherical lens 12 coated with a reflective film is used.
Are arranged on the reflecting surface 5. The hemispherical lens 12 has a structure in which the center of curvature is on the reflecting surface 5 and can move on the reflecting surface 5.

The second embodiment is constructed as described above, and by moving the hemispherical lens 12 slightly, it is possible to easily add an arbitrary number of linear interference fringes. This linear interference fringe can be easily determined when visually measuring the amount of wavefront aberration. Instead of the hemispherical lens 12, FIG.
As shown in, a combination of a spherical lens 13 and a cylindrical glass body 14 made of the same glass material may be used. In this case, the center of curvature of the spherical lens 13 is the cylindrical glass body 14
To be inside.

FIG. 4 is a diagram showing the configuration of a third embodiment of the simple interferometer of the present invention. In the first and second embodiments, the incident wavefront is convergent light, but in the case of this embodiment, the incident wavefront is the parallel incident wavefront 15 and is not a spherical wave. Therefore, an aberration-corrected condenser lens 16 is placed in front of the spherical lens 2 that is in close contact with the cube beam splitter 3, and the parallel incident wavefront 15 is converted into a spherical wave that is convergent light. Further, in this embodiment, the eyepiece 1 is used as the observation means.
It is possible to observe interference fringes with the naked eye 17 by arranging 6.

[0021]

As described above, the simple interferometer of the present invention has a small number of parts and can easily measure the wavefront aberration.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a simple interferometer of the present invention.

FIG. 2 is a diagram showing a configuration of a second embodiment of the simple interferometer of the present invention.

FIG. 3 is a diagram showing a configuration of parts of a second embodiment of the simple interferometer of the present invention.

FIG. 4 is a diagram showing the configuration of a third embodiment of the simple interferometer of the present invention.

FIG. 5 is a diagram showing a configuration of a conventional interferometer used for inspection measurement.

[Explanation of symbols]

 1 Incident Wavefront 2 Spherical Lens 3 Cube Beam Splitter 4 Cube Beam Splitter Bonding Surface 5 Cube Beam Splitter Reflecting Surface 7 Spatial Filter, Pinhole 9 Spherical Lens 10 Imaging Lens 11 Image Sensor 12 Hemispherical Lens 13 Spherical Lens 14 Cylindrical Glass Body 15 Parallel incident wavefront 16 Eyepiece 17 Naked eye

Claims (3)

[Claims] 1. An interferometer for measuring a wavefront aberration of a coherent incident wavefront, comprising: a cube beam splitter for making the coherent wavefront incident and splitting the coherent wavefront into a first optical path and a second optical path. A reflection type spatial filter arranged on the surface of the beam splitter on the first optical path, and arranged so as to have a center of curvature on the spatial filter or on a mirror image of the spatial filter by the cube beam splitter, Further, a spherical lens cemented to a surface on the first optical path of the cube beam splitter or on a surface facing at least one of the surfaces on the second optical path, and the cube beam splitter. And an observation means provided on the optical path. 2. The interferometer according to claim 1, wherein the observing means comprises an image forming lens for forming an image of light emitted from the cube beam splitter, and an image pickup device for receiving the light emitted. 3. The interferometer according to claim 1, wherein the observation means comprises an eyepiece lens.