JPH0545115A - Hologram interferometer - Google Patents

Abstract

PURPOSE:To make it very easy to prepare a reference surface generating a reference wave and to attain shortening of the time for manufacture of an apparatus and lowering of the cost. CONSTITUTION:This hologram interferometer is equipped with a laser light source 1, a pinhole 4 converting a laser beam 2 into a divergent light 5, a beam splitter 6, a collimator lens 7 and a hologram 9 which functions in such a manner that a parallel light 8 obtained by the collimator lens is made to be reflected partially by a semitransparent mirror plane 9a being vertical to this parallel light 8, while part of the residual parallel light 8 is transmitted and diffracted by a hologram surface 9b and a transmitted and diffracted light 10 is applied onto a body 11 to be measured. Moreover, a TV camera 14 for observing interference fringes formed by the interference of a reference light from the hologram 9 with an object light from the body 11 to be measured is provided.

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 an object surface from an ideal shape, and more particularly to a Fizeau type hologram interferometer using a computer-synthesized hologram.

[0002]

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

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

The interferometric method has an advantage that the shape accuracy of the entire surface can be instantly confirmed without contact. Among them, the interferometric method using a computer-synthesized hologram attracts attention because it can measure an object to be measured having a special shape.

Generally, a computer-synthesized hologram is one in which a photoresist coated on a glass substrate is scanned with an electron beam to expose predetermined interference fringes, and then developed to reveal the interference fringes. The predetermined interference fringe is an interference fringe of an object wave and a reference wave, and 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, a beam diameter is narrowed down by a condenser lens 24, and a divergent light 26 is produced by a pinhole 25 having a beam diverging function. It After this, this 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 is incident on the reference lens 31. The reference lens 31 is a lens that acts as a convex lens, and converges the parallel light 30 to a point P on the optical axis, and then irradiates the measured surface 33 with divergent light.

The surface 33 to be measured is a concave mirror having an aspherical surface, 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 surface 33 to be measured is the reference lens 31, the collimator lens 29 and the mirror.
The light enters the half mirror 27 via 28.

The reference surface 31a of the reference lens 31, which faces the surface 33 to be measured, is provided with a special coating so that about half the amount of 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 to 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 constant ratio 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 the function of converting a predetermined aspherical wave into a spherical wave. That is, the reflected light reflected by the reference surface 31a is a spherical wave, but the reflected light that is an object wave reflected by the surface 33 to be measured, which is an aspherical surface, is an aspherical wave, and these lights are directly interfered with each other. The interference fringes obtained at this time become extremely fine according to the difference between these two wavefronts, and its measurement becomes difficult. Reference plane
Although rough interference fringes can be obtained if 31a is an aspherical surface and the reference wave is an aspherical wave corresponding to the object wave, it is difficult to manufacture the reference surface 31a. Therefore, an object wave that is an aspherical wave is converted into a spherical wave by passing it through this hologram, and this spherical wave and the reference wave that is the spherical wave reflected from the reference surface 31a interfere with each other, so that the spherical waves are rough. Interference fringes are formed to facilitate observation with the TV camera 39.

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

[0012]

In the above-mentioned prior art, it is possible to make the reference surface a spherical surface instead of an aspherical surface by using a hologram, which makes the manufacture thereof to some extent easy.

However, it is not always easy to manufacture a highly accurate spherical reference surface. For this reason,
There has been a demand for a hologram interferometer in which the reference plane can be easily manufactured, and the time required for manufacturing the device can be shortened and the cost can be reduced.

The present invention has been made in view of the above circumstances, and it is extremely easy to manufacture the reference surface, and it is possible to shorten the time required for manufacturing the device and reduce the cost.
It is an object of the present invention to provide a hologram interferometer with good measurement accuracy.

[0015]

A hologram interferometer of the present invention comprises a light source for outputting a laser beam, a beam diverging means for diverging a laser beam output from the light source, and a laser output from the beam diverging means. A collimator lens for converting a beam into parallel light and a semi-transparent mirror plane on which the parallel light output from the collimator lens is vertically incident, and the collimated light incident from the semi-transparent plane is refracted to the object under measurement A hologram optical element having a hologram surface that separates the transmitted diffracted light to be emitted and emits these two lights in different directions, is reflected from the DUT, and is re-diffracted by the hologram surface. The diffracted light transmitted through the hologram optical element and the reflected light reflected by the semi-transparent mirror plane may interfere with each other. Is shall.

That is, this hologram interferometer uses a transmissive hologram optical element to reflect a part of the measurement light as a reference wave on the incident plane and to emit the transmitted diffracted light to irradiate the object to be measured on the exit surface. After this, this transmitted diffracted light is reflected from the measured object as an object wave, re-diffracted at the exit surface and transmitted through the hologram optical element, and between the reference wave reflected at the incident plane. It is designed to interfere.

[0017]

According to the above construction, a part of the measuring light is reflected as reference light which is parallel light on the incident plane (semi-transparent mirror plane). On the other hand, a part of the light incident on the hologram optical element is converted into diffracted light having a wavefront according to the surface shape of the DUT by the diffraction effect on the hologram surface,
The object light is reflected by the object to be measured and becomes object light. This object light is converted into parallel light again when re-incident on the hologram exit surface, and passes through the hologram optical element in this state.

Since the object light and the reference light, which are the two parallel lights, are configured to interfere with each other, if the two parallel lights are converged and then made incident on the TV camera or the screen, the object to be received is received. Interference fringes corresponding to the surface shape of the measurement object can be observed.

As described above, in the hologram interferometer of the present invention, the plane reflecting surface can be used as the surface for generating the reference light, and it is not necessary to manufacture an aspherical surface or a spherical reference reflecting surface. Is extremely easy to manufacture.

Therefore, it is possible to shorten the time required for manufacturing the device and reduce the cost.

Further, in the hologram interferometer of the present invention, the transmitted diffracted light guided to the object to be measured and the refracted light are separated on the hologram exit surface of the hologram optical element, and both are emitted in different directions. It is possible to avoid a situation in which the measurement object is irradiated with refracted light, and prevent a decrease in measurement accuracy.

[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 an embodiment of the present invention. This hologram interferometer includes a laser light source 1, a condenser lens 3 that narrows down the laser light 2 emitted from the light source 1, a pinhole 4 that converts the narrowed down laser beam 2 into divergent light 5, and the divergent light 5 A beam splitter 6 that reflects the light in a direction rotated by 90 °, a collimator lens 7 that converts the reflected divergent light 5 into a parallel light 8, and a semi-transparent mirror that makes the parallel light 8 perpendicular to the parallel light 8. A part of the remaining parallel light 8 is partially reflected by the flat surface 9a and a hologram surface is formed.
A hologram (holographic optical element; functioning so as to be transmitted and diffracted by 9b and converge the transmitted diffracted light 10 (first-order diffracted light) to a point O and then diverge and irradiate the object to be measured 11 with it.
HOE) 9.

Further, the center of the radius of curvature of the reflecting surface of the object to be measured 11 coincides with the point O so that the object light generated by the transmitted diffracted light 10 being reflected by the object to be measured 11 goes backward in the incident optical path. The hologram surface 9b is again diffracted, and is transmitted through the collimator lens 7 and reaches the beam splitter 6 together with the reference light generated by being reflected by the semi-transparent mirror plane 9a. It passes through the beam splitter 6.

Further, this hologram interferometer has an image forming lens 13 for forming an image of both the reference light and the object light transmitted through the beam splitter 6, and a light receiving surface on the focal plane of the image forming lens 13. However, the TV camera 14 for observing the interference fringes formed by the reference light and the object light is provided.

Incidentally, the semi-transparent plane 9a and the hologram surface 9b of the hologram 9 are in a non-parallel state, that is, in a so-called wedge shape, and the angle difference between the exit angles of the transmitted diffracted light 10 and the refracted light 12 which are first-order diffracted lights. Is large enough to prevent the refracted light 12 from irradiating the object to be measured 11.

The base of the hologram 9 is made of highly transparent glass or plastic resin. Also,
The semi-transparent mirror plane 9a is a highly flat substrate surface on which aluminum is vapor-deposited to a predetermined thickness, and the hologram surface 9b is coated with a photoresist on the surface opposite to the aluminum vapor-deposited surface, so that the electron The hologram pattern is exposed and developed by a beam.

The pattern of this hologram surface 9b is the object to be measured.
It has a striped pattern shape corresponding to the shape of 11. For example, when the measured object 11 is a cylindrical surface, it has a striped pattern in which straight lines are arranged in parallel.

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

Next, the operation of this hologram interferometer will be described. Here, a case where the device under test 11 is a reflecting mirror having a cylindrical surface will be described.

The hologram 9 to which the parallel light (plane wave) 8 as the measurement light is incident reflects a part of it on the semi-transparent mirror plane 9a to generate reference light (plane wave).

Further, a part of the parallel light 8 that has passed through the hologram 9 and has reached the hologram surface 9b is emitted as refracted light 12, and the first-order transmitted diffracted light 10 is emitted in a direction different from the emission direction of the refracted light 12. Inject.

As described above, when the object to be measured 11 is a reflecting mirror having a cylindrical surface, the above pattern has a striped pattern in which straight lines parallel to the central axis of the cylindrical surface are arranged. When the parallel light 8 irradiates the hologram pattern having a linear striped pattern in this manner, the transmitted diffracted light 10 that does not converge in the extending direction of the stripe but converges in the direction orthogonal to the stripe in the hologram plane. Will be ejected. In this case, the transmitted diffracted light 10 once converges at a point O on the central axis of the cylindrical surface, then diverges and is applied to the entire surface of the object to be measured 11. Therefore, the object light (aspherical wave) reflected from the object to be measured 11 reenters the hologram surface 9b by returning to the optical path of the transmitted diffracted light 10. The object light becomes parallel light again due to the pattern of the hologram surface 9b, overlaps with the reference light that is parallel light specularly reflected by the semi-transparent mirror plane 9a, and interferes with each other to form interference fringes on the light receiving surface of the TV camera 14. To do. That is, in the above embodiment, the hologram surface 9b is used to convert a plane wave into an aspherical wave corresponding to the cylindrical surface.

Since the interference fringes are generated as a result of the interference between the parallel lights, they have a rough fringe pattern and can be detected. The detected striped pattern represents the distortion from the ideal cylindrical surface of the measured object 11, and the measured object can be measured by measuring this striped pattern.
It is possible to detect 11 shapes.

Further, since the interference fringes can be efficiently obtained when the light quantities of the reference light and the object light are about the same, the object to be measured can be efficiently measured.
It is desirable to form the semi-transparent mirror plane 9a and the hologram plane 9b having a reflectance and a diffraction efficiency according to the reflectance of 11.

In the above description, the object to be measured 11 is a reflection plate having a cylindrical surface, but if the object to be measured 11 having such a shape is used, the pattern of the hologram surface 9b can be made into a linear striped pattern, so that it is extremely manufactured. It's easy.

However, even if the object 11 to be measured is a reflecting plate having a spherical surface or other aspherical surface, if the pattern of the hologram surface 9b is a striped pattern of a predetermined curved shape, the hologram interferometer as described above can be used. It is possible to measure its shape.

The hologram interferometer of the present invention is not limited to the above-mentioned embodiment, and various other modifications can be made.

For example, the hologram 9 is not a so-called wedge shape but a so-called flat plate shape in which the semi-transparent mirror plane 9a and the hologram surface 9b are parallel to each other, and the transmitted diffracted light 10 irradiating the measured object 11 uses the first-order diffracted light. Thus, it is possible to separate the transmitted diffracted light 10 and the refracted light 12. However, in this case, since the magnification of the image varies depending on the portion of the object to be measured 11, the magnification is corrected by inclining the imaging surface or the like on which the interference fringes are formed by a predetermined angle. Is preferred.

Further, 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.

Instead of the TV camera 14, a recording medium may be placed at that position to record the interference fringes, or the interference fringes may be directly observed at the position.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a hologram interferometer according to an 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 Divergence light 6 Beam splitter 7,29 Collimator lens 8,30 Parallel light 9,34,34a Hologram 9a Semi-transparent plane 9b Hologram Surface 10 Transmitted diffracted light 11,33 DUT 12 Refracted light 14,39 TV camera 38 Filter 31 Reference lens 31a Reference surface 35 Field lens

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[Procedure amendment]

[Submission date] September 13, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0039

[Correction method] Change

[Correction content]

For example, the hologram 9 does not have a so-called wedge shape but a so-called flat plate shape in which the semi-transparent mirror plane 9a and the hologram surface 9b are parallel to each other, and the transmitted diffracted light 10 irradiating the DUT 11 becomes off-axis light. Thus, it is possible to separate the transmitted diffracted light 10 and the refracted light 12.
However, in this case, since the magnification of the image varies depending on the portion of the object to be measured 11, the magnification is corrected by inclining the imaging surface or the like on which the interference fringes are formed by a predetermined angle. Is preferred.

Claims (1)

[Claims] 1. A light source for outputting a laser beam, a beam diverging means for diverging a laser beam output from the light source, a collimator lens for converting the laser beam output from the beam diverging means into parallel light, The parallel light output from the collimator lens has a semi-transparent mirror plane that is vertically incident, and the parallel light that is incident from the semi-transparent mirror plane is separated into refracted light and transmitted diffracted light that is irradiated to the measured object A hologram optical element having a hologram surface that emits two lights in different directions, and transmitted diffracted light that is reflected from the object to be measured, re-diffracted by the hologram surface, and transmitted through the hologram optical element. A hologram interferometer, characterized in that the reflected lights reflected by the semi-transparent mirror plane are configured to interfere with each other.