JP3010085B2 - Hologram interferometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram interferometer for measuring a deviation of a surface of an object from an ideal shape, and more particularly to a hologram interferometer using a hologram optical element.

[0002]

2. Description of the Related Art Interferometry is known as a technique for precisely measuring the surface shape of a spherical or aspherical surface.

In the shape measurement by the interferometry, the degree of displacement of the surface to be measured with respect to a highly accurate reference surface (interference standard) is determined by interference fringes generated by interfering light reflected from each surface. It is intended to be obtained based on this.

[0004] The interferometry has the advantage that the shape accuracy of the entire surface can be instantaneously confirmed in a non-contact manner. Among them, the interferometry using a computer-generated hologram has attracted attention because it can measure a special shape.

In general, computer-generated holograms are obtained by exposing predetermined interference fringes by scanning a photoresist applied on a glass substrate with an electron beam, and then developing the exposed interference fringes to make the interference fringes visible. This predetermined interference fringe is a fringe equivalent to the interference fringe of the object wave and the reference wave,
When the same reproduction wave as the reference wave is incident on this interference fringe, the object wave is reproduced.

Conventionally, as an interferometer using such a hologram, one configured as shown in FIG. 2 is known.

That is, in this interferometer, a laser beam 22 emitted from a laser light source 21 is reflected by a mirror 23, the beam diameter is narrowed by a condenser lens 24, and is diverged by a pinhole 25 having a beam diverging function. You. Thereafter, the divergent light 26 passes through the half mirror 27, is reflected by the mirror 28, is converted into parallel light 30 by the collimator lens 29, and enters the reference lens 31. The reference lens 31 is a lens acting as a convex lens, and converges the parallel light 30 to one point 0 on the optical axis, and thereafter irradiates the divergent light onto the surface 33 to be measured.

The surface 33 to be measured is a mirror functioning as an aspherical concave mirror, and its position is adjusted so that the reflected light returns along the path of the incident light. Therefore, the reflected light reflected by the measured surface 33 is reflected by the reference lens 31 and the collimator lens 29.
And enters the half mirror 27 via the mirror 28.

The reference surface 31a of the reference lens 31 facing the surface 33 to be measured is provided with a special coating so that about half of the light is transmitted and the rest is reflected. The reflected light that is the reference light reflected by the reference surface 31a is also formed so as to return along the path of the incident light that has entered the reference lens 31. These two reflected lights are reflected by the half mirror 27 at a fixed rate, and enter the TV camera 39 via the hologram 34, the field lens 35, the imaging lens 36, the mirror 37, and the spatial filter 38.

The hologram 34 has a function of converting a predetermined aspherical wave into a spherical wave. That is, while the reflected light reflected by the reference surface 31a is a spherical wave, the reflected light, which is an object wave reflected from the measured surface 33, which is an aspheric surface, is an aspherical wave. The resulting interference fringes are extremely fine according to the difference between these two wavefronts, and their measurement is difficult. Reference plane
Although rough interference fringes can be obtained if the reference wave is an aspherical wave corresponding to the object wave when the reference surface 31a is an aspherical shape, there is a problem that it is difficult to manufacture the reference surface 31a. Then, the object wave, which is an aspherical wave, is converted into a spherical wave by passing through the hologram, and the spherical wave and the reference wave, which is a spherical wave reflected from the reference surface 31a, are interfered with each other to form a rough spherical wave. Interference fringes are formed so that observation with the TV camera 39 is facilitated.

When the surface 33 to be measured is a convex surface, the hologram 34a is provided at a position conjugate to the hologram 34, instead of the hologram 34.

[0012]

In the prior art described above, the reference surface can be made to be a spherical surface instead of an aspherical surface by using a hologram, thereby making the manufacturing thereof somewhat easy.

However, it is not always easy to manufacture a highly accurate spherical reference surface.

Further, when inspecting a plurality of surfaces to be inspected, if the reflectances of the surfaces to be inspected are largely different from each other, the amounts of the reflected lights forming the object wave are greatly different from each other. In order to efficiently generate interference fringes, it is necessary to change the reflectance of the reference surface 31a according to the reflectance, and it is necessary to change the reference lens 31 each time.
For this reason, there has been a problem that the time required for the measurement or the cost is high.

The present invention has been made in order to solve such a problem, and it is extremely easy to manufacture a reference surface, and it is possible to measure a surface to be inspected having a different reflectance in a short time. It is an object of the present invention to provide a hologram interferometer in which the manufacturing cost of the apparatus is low.

[0016]

A hologram interferometer according to the present invention comprises a light source for emitting a laser beam, a beam diverging device for diverging a laser beam emitted from the light source, and a laser beam emitted from the beam diverging device. A collimator lens that converts the beam into parallel light, a hologram optical element that reflects the parallel light emitted from the collimator lens in one direction and diffractively reflects the object to be measured, and a parallel light that is reflected from the hologram optical element. It is provided with a planar reference reflector for reflection, and the reflected light reflected from the reference reflector and the reflected light reflected from the measured object are reflected by the hologram optical element and can interfere with each other. It is characterized by being done.

That is, this hologram interferometer uses a reflection type hologram optical element to convert the incident measurement light into two.
In the first direction, which is parallel light among the reflected lights.
Is reflected by the planar reference reflector, and the second reflected light corresponding to the surface shape of the measured object is reflected by the measured object. It is characterized in that interference fringes are formed by interfering with an object wave which is reflected light from an object to be measured.

[0018]

According to the above construction, the measuring light is reflected in two directions by the hologram optical element, and the first reflected light among these reflected lights is parallel light, and is reflected by the planar reference reflecting plate. To form a reference wave. On the other hand, of these reflected lights, the second reflected light is converted by the diffraction action of the hologram optical element so as to have a wavefront corresponding to the surface shape of the measured object, and is reflected by the measured object to convert the object wave. Form. Thereafter, the reference wave is reflected by the hologram optical element in a state of parallel light, while the object wave is converted by the hologram optical element into parallel light and reflected.

Since the two parallel lights interfere with each other, if the two parallel lights are converged and then made incident on a TV camera or a screen, the two parallel lights are adjusted according to the surface shape of the object to be measured. Interference fringes can be observed.

As described above, in the hologram interferometer of the present invention, it is possible to use a planar reflector as a surface for generating a reference wave, and it is not necessary to manufacture an aspherical or spherical reference reflector. Is extremely easy to manufacture.

Also, when measuring a plurality of objects to be measured having different reflectivities, it is sufficient to prepare a flat reflector having a different reflectivity, and the arrangement position thereof can be easily adjusted. Thus, the time required for the measurement can be reduced, and the cost can be reduced.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a hologram interferometer according to one embodiment of the present invention. The hologram interferometer includes a laser light source 1, a condenser lens 3 for narrowing a laser beam 2 emitted from the light source 1, and a pinhole 4 for converting the narrowed laser beam 2 from which a noise component has been removed to a diverging light 5. A beam splitter 6 for reflecting the divergent light 5 in a direction rotated by 90 °, a collimator lens 7 for converting the reflected divergent light 5 into a parallel light 8, and a first reflection of the parallel light 8 by regular reflection. A reflected light 10 is formed, and the parallel light 8 is reflected and diffracted to form a second reflected convergent light.
Hologram (hologram optical element; HO) forming 11
E) a reference reflector 12 having a reference reflection surface 12a perpendicular to the first reflected light 10 and reflecting the first reflected light 10 in the direction of the hologram 9;

Further, the light which is the reference wave reflected from the reference reflector 12 and the light which is the object wave reflected from the measured object 13 are reflected by the hologram 9 in the backward direction of the incident optical path and transmitted through the collimator lens 7. Then, the light reaches the beam splitter 6 and thereafter passes through the beam splitter 6.

Further, the hologram interferometer has an imaging lens 14 for imaging both the reference wave light and the object wave light transmitted through the beam splitter 6, and a light receiving surface on a focal plane of the imaging lens 14. In addition, a TV camera 15 for observing interference fringes formed by the reference wave light and the object wave light is provided.

The hologram 9 is a flat optical element formed by coating a photoresist on a glass substrate, exposing and developing a hologram pattern by an electron beam, and then coating aluminum thereon.

The pattern of the hologram 9 is
For example, when the measured object 13 is a cylindrical surface, the stripe pattern is a stripe pattern in which straight lines are arranged in parallel.

The size of the hologram 9 is, for example, 5 inches square.

The beam splitter 6 is an optical element for dividing incident light into transmitted light and reflected light, and reflects about half of the divergent light incident from the direction of the pinhole 4 toward the collimator lens 7 while the collimator It functions so that approximately half of the convergent light incident from the lens 7 direction is transmitted to the TV camera 15 direction.

Next, the operation of the hologram interferometer will be described. The case where the measured object 13 is a reflecting mirror having a cylindrical surface will be described.

The hologram 9 on which the parallel light 8 as the measuring light is incident emits a first reflected light 10 which is a regular reflection light, similarly to a normal reflector.

At the same time, the parallel light 8 is reflected and diffracted by the hologram pattern, and the second reflected light 11 converged in the direction of the measured object 13 is emitted.

As described above, when the measured object 13 is a reflecting mirror having a cylindrical surface, the above-described pattern forms a stripe pattern in which straight lines parallel to the central axis direction of the cylindrical surface are arranged. When the parallel light 8 is applied to the hologram pattern forming the linear stripe pattern, the second reflection does not converge in the direction in which the stripes extend, but converges in the hologram plane and in the direction orthogonal to the stripes. Light 11 will be emitted. In this case, the second reflected light 11 once converges on the central axis of the cylindrical surface, diverges, and irradiates the entire surface of the measured object 13. Therefore, the object wave light reflected from the measured object 13 enters the hologram 9 so as to return along the optical path of the second reflected light 11. The hologram 9
The light beam becomes parallel light by the above pattern, and overlaps with the reference wave light from the reference reflector 12 which is regularly reflected as parallel light on the hologram 9 and interferes with each other to form an interference fringe on the light receiving surface of the TV camera 15. That is, in the above embodiment, the hologram 9 causes the conversion between the plane wave and the aspherical wave corresponding to the cylindrical surface.

Since this interference fringe is generated as a result of interference between parallel lights, it has a coarse fringe pattern, and can be detected. The detected stripe pattern represents a distortion from the ideal cylindrical surface of the DUT 13, and by measuring this stripe pattern, the DUT is measured.
Thirteen shapes can be detected.

Since the interference fringes can be efficiently obtained when the light amounts of the reference wave light and the object wave light are substantially the same, the reference reflector 12 having a reflectance corresponding to the reflectance of the measured object 13 is provided. It is desirable to do.

In the above description, the measured object 13 is a reflecting plate having a cylindrical surface. However, with the measured object 13 having such a shape, the pattern of the hologram 9 can be formed into a linear stripe pattern, so that manufacture is extremely easy. It is.

However, even if the measured object 13 is a reflecting plate having a spherical or other aspherical shape, if the pattern of the hologram 9 is a stripe pattern having a predetermined curved shape, the hologram interferometer as described above is used. It is possible to measure the shape.

It should be noted that the hologram interferometer of the present invention is not limited to the above-described embodiment, and other various changes can be made.

For example, a half mirror may be used as the beam splitter 6, or the beam splitter 6
May be arranged between the collimator lens 7 and the hologram 9.

In place of the TV camera 15, the recording medium may be placed at the position to record the interference fringes, or the interference fringes may be directly observed at the position.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a hologram interferometer according to one embodiment of the present invention.

FIG. 2 is a schematic diagram showing a hologram interferometer according to the related art.

[Explanation of symbols]

 1,21 laser light source 2,22 laser beam 3,24 condenser lens 4,25 pinhole 5,26 divergent light 6 beam splitter 7,29 collimator lens 8,30 parallel light 9,34,34a hologram 10 first reflected light 11 Second reflected light 12 Reference reflector 13, 33 Measurement object 15, 39 TV camera 38 Filter 31 Reference lens 31a Reference surface 35 Field lens

Claims (1)

(57) [Claims] A light source for emitting laser light; a beam diverging means for diverging a laser beam emitted from the light source; a collimator lens for converting the laser beam emitted from the beam diverging means into parallel light; A hologram optical element for reflecting parallel light emitted from the collimator lens in one direction and diffracting and reflecting toward the object to be measured; and a planar reference reflector for reflecting the parallel light reflected from the hologram optical element. A hologram interferometer, wherein reflected light reflected from the reference reflector and reflected light reflected from the measured object are reflected by the hologram optical element and can interfere with each other.