JPH0585843B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a holographic interferometer for precisely measuring the surface shape of optical elements such as lenses and mirrors, especially aspherical optical elements, using a hologram prototype. More specifically, the present invention relates to a holographic interferometer having monitoring means for monitoring the amount of tilt of an optical surface for generating a reference wavefront.

Prior Art As a method for measuring the surface shape of an aspherical optical element, a hologram prototype created by interference between a reflected or transmitted wavefront from a reference aspherical surface and a reference light wavefront, or optical design values of a reference aspherical surface is used. A so-called "computer-generated hologram", which is created by calculating a hologram pattern using an electronic computer and using an electron beam drawing method, is used as a hologram prototype, and the diffracted light by the hologram prototype of the reflected or transmitted wavefront from the aspherical optical element to be tested is used. A holographic interferometer is known in which the error of the aspherical optical element under test from the reference aspherical surface is precisely measured by interfering the aspherical surface with a reference light and the amount and shape of the interference fringes.

Further, as an interferometer, for example, a Fizeau type interferometer shown in FIG. 22 is known. That is,
The light from the light source (laser) LS is collimated by a collimator lens C. Then, the imaging lens L ₁
A part of the light beam reflected by the beam splitter BS, which is a half mirror tilted between the diverging lens _L2 and the diverging lens _L2 , is reflected by the reference sphere R after being diverged by the diverging lens L2. , passes through the same optical path as the incident light (l ₁ ), passes through the beam splitter BS, the hologram prototype H, and the imaging lens L ₁ to become a zero-order reference light and passes through the aperture of the spatial filter SF.

On the other hand, the light that passes through the reference spherical surface R and is reflected by the optical element to be tested (aspherical concave mirror) T, that is, the object light, travels backwards and passes through the beam splitter BS.
The 0th-order light that passes through the beam splitter BS and is not diffracted by the hologram prototype is cut off by the spatial filter SF, while the 1st-order diffracted light, for example, which is diffracted by the hologram prototype, passes through the aperture of the spatial filter SF and is cut off by the spatial filter SF. Interference fringes are formed on an interference screen or film with the zero-order reference light.

Furthermore, as measurement methods using conventional holographic interferometers, on-axis methods and off-axis methods are known. The on-axis method is a method in which the object beam and the reference beam are coaxial and measurements are taken, while the off-axis method is a method in which the object beam and the reference beam are measured non-coaxially, that is, the propagation axis of the object beam and the propagation axis of the reference beam are tilted to each other. This is a type of measurement method that intersects. The on-axis method and the off-axis method each have advantages and disadvantages, and it is necessary to use them properly depending on the object to be examined.

Problems to be Solved by the Invention When measuring by the off-axis method, the off-axis angle, that is, the angle formed by the mutual propagation axes of the object beam and the reference beam, is optimal depending on the type of specimen and the degree of asphericity. Since the value of is determined, it differs for each test object or for each corresponding hologram prototype.

For this reason, it is necessary to change the off-axis angle, that is, the inclination angle (tilt amount) of an optical member for generating a reference wavefront, such as a flat semi-transparent mirror, each time a test object or a hologram prototype is set in the interferometer body. However, since the conventional holographic interferometer does not have a means for monitoring the amount of tilt of the optical member for generating the reference wavefront, it has not been possible to check whether or not the propagation axis of the normal reference wavefront has been obtained.

In addition, if it is desired to be able to use both the on-axis method and the off-axis method with a single holographic interferometer, the amount of tilt of the reference wavefront generation optical member is made variable, and when the on-axis method is used, the reference wavefront generation surface is must be perpendicular to the optical axis. Therefore, it is necessary to check whether the reference wavefront generation surface is exactly perpendicular to the optical axis, but conventionally there was no means for checking this on-axis state.

For this reason, conventional holographic interferometers have the disadvantage that the reference wavefront generation surface is often not set at the angle required for measurement, resulting in errors in the measurement results.

OBJECTS OF THE INVENTION An object of the present invention is to provide a holographic interferometer that can accurately set the on-axis state and off-axis angle.

Structure of the Invention The structure of the holographic interferometer of the present invention for achieving the above object includes a light source, a collimator lens for projecting the light from the light source onto an object as a parallel beam, and the collimator lens. and a hologram prototype that diffracts at least one of the reflected light wavefront from the object to be measured and the reference wavefront from the reference wavefront generation optical surface, which is disposed behind the reference wavefront generation optical surface. The present invention is an optical interferometer characterized by having a monitoring means for monitoring an intersection angle between the reference wavefront generating optical surface and the optical axis of the collimator lens.

Effects of the Invention According to the present invention, since the arrangement angle of the reference wavefront generating optical surface can be monitored, the reference wavefront propagation axis, which is the basis for high-precision measurement, can be accurately positioned in both on-axis and off-axis methods.

Embodiments Hereinafter, embodiments of the holographic interferometer according to the present invention will be described in detail.

A. Overall optical configuration FIG. 1 shows an overall diagram of the optical configuration of a holographic interferometer according to the present invention. Light from a laser 101 as a light source has its optical path changed by mirrors 102a and 102b, and then is condensed by a condenser lens 103. There is a pinhole near this focal point.
A pinhole reticle plate 104 having a diameter of 04a is arranged. The diverging light passing through the pinhole 104a acts as if the pinhole 104a were a secondary light source. Note that the mirrors 102a and 102
A 1/4 wavelength plate 105 is disposed between the wavelengths b.

A collimator lens 106 is arranged so that its focal point is located at the pinhole 104a.
A light beam emitted from the pinhole 104a using the pinhole 104a as a secondary light source is made into a parallel light beam by a collimator lens 106. A reference plane plate 107 is arranged behind the collimator lens 106. This reference plane plate 107 is the front plane 10
7a is arranged perpendicular to the apparatus optical axis (collimator optical axis) _O1 . Further, the rear plane 107b is inclined at a small angle with respect to the front plane 107a, so that interference light between the light reflected from the front plane 107a and the light reflected from the rear plane 107b does not affect the measurement. It's summery.

When the test object T is a concave object such as an aspherical concave mirror, a reference lens 109 is attached to the apparatus lens barrel 108 and arranged behind the reference plane plate 107 . The parallel light beam transmitted through the reference plane plate 107 becomes a convergent light beam, and after converging once at point P,
It becomes diverging light again and hits the object to be inspected, for example, an aspherical concave mirror T.
incident on .

The object light reflected from the test object T and the reference light reflected from the front plane 107a of the reference plane plate 107 are connected to the half mirror surface 11 between the pinhole reticle plate 104 and the collimator lens 106.
0a is incident on a prism type beam splitter 110 tilted with respect to the optical axis _O1 . Both the object light and the reference light are reflected by the half mirror surface 110a and enter a hologram prototype 300 supported by a hologram prototype holder 200, which will be described later.

Laser 101, mirrors 102a, 102b, 1/
4-wave plate 105, pinhole reticle 104, zoom splitter 110, collimator lens 10
6. The reference flat plate 107, the reference lens 109, the test object T, and the hologram prototype holder 200 are installed on one common optical bench 100.

The light transmitted through the hologram prototype 300 is imaged on a spatial filter 113 via an imaging lens 111 and a half mirror 112. This spatial filter 113 is for selectively extracting only one of the reference light and the object light that was diffracted by the hologram prototype 300 and the other light that was not diffracted by the hologram prototype 300. . To be more specific, as in the conventional Fizeau interferometer shown in FIG. A hologram prototype 30 is created using the reference light and the object light from the test object T.
It selectively extracts only the first-order object light diffracted at zero, and cuts out the diffracted light of the reference light and the zero-order, second-order and higher-order diffraction lights of the object light.

The object light and reference light selected by the spatial filter 113 are passed through the zoom lens 114 and the half mirror 11.
5 and the TV camera 11 via the imaging lens 116.
An interference pattern between the reference light and the object light is formed on the imaging surface 117a of No. 7. The image captured by the TV camera 117 is sent to an interference pattern analysis device 119 consisting of a monitor television 118 and a personal computer. Note that the reference light and object light that have passed through the half mirror 115 form a similar interference pattern when formed on the imaging surface 117a of the film 120a of the instant development type camera 120.
Record on 0a.

A portion of the light that has passed through the imaging lens 111 is transmitted through a half mirror 112 and is imaged on a reticle plate 121 arranged with the crosshairs aligned with the optical axis.
The image on the reticle plate 121 is captured by a TV camera 123 via a photographing lens 122, and the switching circuit 12
4 on the monitor 118. These reticle plate 121, photographing lens 122, TV camera 123, and monitor 118 are connected to an alignment optical system 1 for setting the object T in the measurement optical path.
Form 25.

Imaging lenses 111, 116, half mirror 11
2,115, spatial filter 113, zoom lens 114, photographic lens 122, TV camera 11
7, 123 and the camera 120 are the optical bench 13
0. This optical bench 130 has an arm that rotates by driving a known micro-feeding mechanism 131 around a point LC that is conjugate to the exit pupil EP of a composite optical system of a collimator lens 107 and a reference lens 109 in order to adjust the off-axis angle described later. 131
It is fixedly installed. Note that when the object to be inspected is a flat object, the reference lens 109 is not necessary, and in this case, the center of rotation LC is set at a position conjugate with the center of the exit pupil of the collimator lens 107.

As described above, since the present holographic interferometer is of the Fizeau type, the number of optical elements can be significantly reduced compared to the Twyman-Green type and Matsuhatsu-Ender type. Furthermore, unlike the conventional Fizeau type interferometer, this interferometer has its beam splitter placed in the diverging beam between the collimator lens and the pinhole 104a. The area of the half mirror surface is 1/4 compared to that of the original.
It can be made as small as possible.

Furthermore, by narrowing the half mirror surface, the beam splitter can be constructed in a prism type, and as will be described later, it is possible to reduce calculation information and drawing information for drawing a hologram pattern. Furthermore, since the beam splitter has become smaller, its manufacturing precision can be significantly improved, and its manufacturing cost can also be reduced.

Furthermore, since the hologram prototype is also arranged within the convergence and reflection beam of the beam splitter, it is possible to reduce the size, reduce costs, and achieve high-precision drawing. This has made it possible to create a holographic interferometer that can measure with high precision even large-diameter test objects and highly aspherical test objects.

B Hologram Prototype Figure 2 is a plan view showing the configuration of the hologram prototype. The hologram prototype 300 has a hologram pattern section 301 made of a computer-generated hologram in the center. Conventional interferometers use mirror-type beam splitters to separate and combine the reference beam and object beam.
In the case of this mirror type beam splitter, if the mirror surface and mirror back surface (half mirror surface) are formed in parallel, the light reflected from each surface will interfere with each other and adversely affect the measurement. The beam splitter had the mirror surface and mirror back surface not parallel to each other but tilted at a slight angle. As a result, the symmetry with respect to the optical axis is disrupted, and conventionally, even in the case of an on-axis hologram prototype, the hologram pattern had to be calculated for all quadrants to obtain drawing data. but,
In this holographic interferometer, the beam splitter 110 is a prism type beam splitter as described above, so symmetry with respect to the optical axis is preserved, and the hologram pattern of the on-axis hologram prototype is a concentric circle pattern. Point symmetry. For this reason, the pattern calculation and drawing data calculation are performed using (x, y) as shown in Figure 4.
This is done only for the first quadrant of , and the other (-x, y),
For the second, third, and fourth quadrants of (-x, -y) and (x, -y), it is sufficient to simply coordinate transform the data in the first quadrant, reducing calculation costs and calculation time, and rendering Data can be reduced. On the other hand, if the same amount of expense and time as in the past is spent on calculating hologram patterns and creating drawing data, those data can have higher precision.

A cross-shaped distortion test pattern 302 is formed around the hologram pattern section 301, which is drawn at the same time as the hologram pattern is drawn by electron beam scanning. This distortion test pattern is compared with a reference pattern created in advance, and the amount of distortion of the hologram pattern can be tested from the amount of mutual positional deviation.

Further, a black-white ratio test pattern 303 is formed at two locations outside the distortion test pattern. This black-and-white ratio test pattern is, for example, a checkered pattern in which black portions 304 and white portions 305 of the same area are alternately arranged in a plane as shown in FIG. 3.
This black-and-white ratio test pattern 303 is drawn at the same time as the hologram pattern 301 is written with an electron beam, so this black-and-white ratio test pattern 303
By measuring the black and white ratio of the hologram pattern using a densitometer, the black and white ratio of the hologram pattern itself can be indirectly known.

The hologram prototype 300 is placed in a hologram prototype holder 200 at each corner of the hologram prototype 300.
A cross-hair-shaped alignment mark 306 is formed for alignment when attaching to. An L-shaped upper/lower discrimination mark 307 is formed below the two alignment marks on the lower side of the figure.

C Hologram Prototype Holder FIGS. 5 to 7 are diagrams showing the hologram prototype holder 200. A shaft 203 is supported by bearings 201 and 202 placed on the optical bench 100 so as to be slidable in parallel to the optical axis O ₂ (see FIG. 1). The shaft 203 has a screw 204,
A stage 205 moving in the Z-axis direction (optical axis _O2 direction) is fixed by 204. A cylinder 206 is attached to the bearing 201, and a spring 20 is installed in the cylinder 206.
7 is inserted. On the other hand, a Z-axis feed screw 208 is screwed into the bearing 202 . This Z-axis feed screw 208 cooperates with the spring 207 via a steel ball 209 to clamp the Z-axis direction moving stage 205, and by its feeding, the stage 205 is moved back and forth along the Z-axis direction.

Stage surface 20 of Z-axis direction movement stage 205
An XY direction moving stage 211 is placed on 5a via a steel ball 210. This stage 21
On the back side of 1, there are screws 212 as shown in Figure 6.
is implanted, and the Z-axis direction moving stage 205
The rod 21 passed to the rear of the opening 213 formed in
A spring 215 is hung between the 4 and 4. The tensile force of the spring 215 pulls the X-Y direction moving stage 211 toward the stage surface 205a of the Z-axis direction moving stage 205, thereby stabilizing the moving surface.

Further, the Z-axis direction moving stage 205 has two Y-axis feed screws 216, 21, as shown in FIG.
7 and one X-axis feed screw 218 are attached. The side surface of the XY direction moving stage 211 has guides 220 via bearings 219, and these guides 220 are pressed by feed screws 216, 217, 218 via steel balls 221.

The X-Y direction moving stage 211 further has a notch 2 on the side opposite to the mounting position of the X-axis feed screw 218.
It has 22. A resilient body 223 is inserted between the side surface of the notch 222 and the upright piece 224 of the Z-axis direction moving stage 205.

As shown in FIG. 6, the elastic body 223 includes a cylinder 225, a piston 226 inserted into the cylinder, and a spring 227 inserted into the cylinder 225 to constantly apply a pressing force to the piston 226. It consists of

Similarly, the stage 211 has notches 228 and 22
9 are formed facing the Y-axis feed screws 216, 217, and the upright pieces 230, 2 of the stage 205
31 and the sides of these notches, the elastic body 23
2,233 are interposed. Pressure body 232,2
The structure of 33 is the same as that of the elastic body 223 described above.

In the configuration of the hologram prototype holder described above, by feeding the feed screws 216 and 217 in the same direction and by the same amount, the stage 211 can move an amount Y as shown in FIG. 10B. In addition, the feed screw 21
8, the stage 211 moves to the 10th A.
The amount of movement X is obtained as shown in the figure. Furthermore, by fixing the feed screws 216 and 218 and feeding only the feed screw 217, as shown in FIG. 10C,
The stage 211 is rotated by a rotation angle θ.

The X-Y direction moving stage 211 has a substantially rectangular opening 235 at its center, and circular openings 236 and 237 at the upper left corner and lower right corner. These circular openings 236 and 237 correspond to an opening 238 formed in the Z-axis direction movement stage 205. A microscope objective lens 240 for observing the alignment mark 304 on the hologram prototype 300 is inserted into the opening 238 .

Further, a circular groove 241 is formed around the opening 235 of the stage 211, and a nozzle 242 of a vacuum pump (not shown) is inserted into the pipe 243.
are connected via. Furthermore stage 211
A guide piece 244 is fixed to the outer surface of the holder.
As a result, the hologram prototype 300 is placed on the stage 211 along the guide piece, and the air in the groove 241 is absorbed by the vacuum pump.
11 at atmospheric pressure.

An arm 246 is attached to the tip of the shaft 203 and the tip of the pole 245 implanted in the stage 205.
247 is attached, and its arm 246,
A light emitting diode 248 and a heat ray absorption filter 249 are housed at the tips of the holograms 247, respectively, and are used to illuminate the alignment marks 304 of the hologram prototype placed on the stage 211.

FIG. 8 is a perspective view schematically showing a hologram prototype alignment optical system 250 attached to the hologram prototype holder 200 having the above-described configuration. The alignment optical system 250 includes the above-mentioned light emitting diode 248 and heat ray absorption filter 24.
9. A first optical path 253 consisting of an objective lens 240, a mirror 251, and a beam splitter 252, a light emitting diode 248, and a heat absorption filter 24
9, a second optical path 255 consisting of an objective lens 240, a mirror 251, and a beam splitter 252; and an eyepiece optical path 256, in which the first optical path 253 and the second optical path 255 are combined by the beam splitter 252.

This eyepiece optical path 256 is connected to reticle plates 257 and 258 that move within a plane (xy plane) perpendicular to the optical axis O ₃ and the eyepiece lens 2 by a known moving means (not shown).
59, and circular indicators 260, 261 as shown in FIG. 9 are formed on the reticle plates 257, 258.

As described above, according to this hologram prototype holder, the X-direction moving stage and the Y-direction moving stage are
These X, Y, θ rotation stages can be
Movements related to can be performed in one stage. Also, the configuration for this is extremely simple,
It also has the advantage of allowing highly accurate movement control and positioning.

D Measuring device for off-axis quantities Measurement methods using interferometers generally include on-axis measurement methods and off-axis measurement methods.

The on-axis type refers to a measurement type in which the object light from the test object and the reference light from the reference plane are coaxial, and because the spatial frequency of the hologram prototype used for measurement can be lowered, it can also be used for test objects with a large degree of asphericity. It has measurable benefits. However, on the other hand, the diffracted light from the 0th order to the higher order by the hologram prototype is all superimposed on the optical axis, although their focal lengths are different.For example, in order to extract the first order diffracted light, a spatial filter is placed at the focal position. Also, the inside of that filter is 0
A portion of the second and higher order diffraction light also passes through this spatial filter. Therefore, there is a drawback that the central part including the optical axis becomes an unmeasurable part.

On the other hand, with the off-axis type, unlike the on-axis type mentioned above, unmeasurable parts do not occur, but because the spatial frequency of the hologram prototype is higher than that with the on-axis type, it is difficult to manufacture and align the hologram prototype. Due to limitations, for example, only aspherical objects with small degrees of asphericity can be measured.

Furthermore, since the off-axis angle varies depending on the type of object and the amount of asphericity, when creating a hologram prototype, the optimal off-axis angle is determined in advance. Therefore, the holographic interferometer of this embodiment is configured as an interferometer that is capable of both on-axis and off-axis measurements and has a variable off-axis angle.

FIG. 11 is an optical layout diagram schematically showing on-axis measurement and off-axis measurement. For on-axis measurements, the reference plane plate 107 is aligned perpendicular to the optical axis O ₁ of the collimator lens 106 .
An observation optical system for observing the interference pattern between the object light and the reference light, that is, a spatial filter 113, a zoom lens 114, an imaging lens 116, and an imaging tube 1.
17 are arranged on the optical axis _O2 perpendicular to the optical axis _O1 .

A spatial filter 113 is arranged at the focal position of the first-order diffracted light of the diffracted light by the hologram prototype 300 of each of the object light and reference light, and interference fringes between the first-order diffracted light of the object light and reference light are formed. This will be imaged with an image pickup tube or photographed.

On the other hand, in the case of on-axis measurement, the reference plane 107 is rotated by an angle α (this angle α is referred to as an off-axis angle), as shown by a broken line. The observation optical system is rotated by an angle β together with the optical bench 130 about the rotation center LC. Here, the turning angle β is determined as tanβ=2f tan α/L (here, f is the focal length of the collimator lens).

As a result, only the 1st-order diffracted light of the object light by the hologram prototype 300 and the 0th-order diffracted light of the reference light pass through the spatial filter 113' (spatial filter 113 during off-axis), and both interference fringes are observed and photographed. It is configured so that it can be done.

The off-axis angle α is such that the reflected light (reference light) from the reference plane passes through the half mirror surface 110a of the beam splitter 110 and is reflected by the pinhole reticle 1.
This can be determined from the imaging position of the image S formed on 04. That is, the amount of deviation between the imaging position and the optical axis O ₁ is proportional to the small off-axis angle α.

FIG. 12 is a plan view showing the structure of the pinhole reticle 104. A pinhole 104a is formed at one end of the reticle 104, and a scale 401 is formed along the longitudinal direction from there to the other end. The scale 401 is graduated according to the amount of deviation of the spot S from the optical axis O ₁ (the center of the pinhole 104a) corresponding to the off-axis angle α, and scale numbers 402 of the off-axis angle are printed below these graduations. There is.

FIG. 13 shows an off-axis angle adjusting microscope 410 used when setting the off-axis angle α.
FIG. The microscope 410 has an objective lens 411, converts light from a scale 401 on the reticle 104 and off-axis angle scale numbers 402 into parallel light, reflects it on a mirror 412, and forms an image on an aperture 414 with an imaging lens. A scale image and an off-axis scale numeral image are observed through the eyepiece 415.

FIG. 14 shows the optical arrangement of the on-axis adjustment microscope 420. The difference in configuration from the off-axis angle adjustment microscope 410 described above is that the mirror 4
12 is changed to a half mirror 421, and there is no objective lens 411, and the condensing lens 103 of the interferometer
The point is that it works together with the imaging lens 413 to form an image.

If the running direction of the scale 401 of the pinhole reticle 104 is made parallel to the rotating direction of the reference flat plate 107, and the spot S is projected with a vertical deviation from the scale 401, the surface of the reference flat plate 107 may be tilted or , since it can be determined that the optical axis O has rotated by _one rotation, these checks can also be made.

E Interferometer adjustment method a Setup for on-axis measurement type (on-axis type arrangement of measurement optical system) a-1: Adjust the on-axis adjustment microscope 420 with a collimator as shown by the two-dot chain line in Figure 1. Set it on the optical axis _O1 of the lens 106.

a-2: Half mirror 421 of microscope 420
It passes through the pinhole 10 with the condensing lens 103.
Reference plane plate 107 for the light beam focused on 4a
The reflected spot image S is again pinhole 1.
It is observed through the eyepiece lens 415 whether the image is formed on 04a.

The spot light is observed by the eyepiece lens 415 only when the spot S coincides with the pinhole 104a. A reference plane plate 107 is installed so that the spot S can be observed through the eyepiece lens 415.
Adjust. When the spot S is observed, the reference plane plate 107 is perpendicular to the optical axis _O1 , and the interferometer is in an on-axis arrangement.

(Setting the adjustment lens) a-3: Switch the changeover switch 124 to set the TV camera 123 of the alignment optical system 125.
The monitor TV 118 is set so that images from the TV are displayed on the monitor TV 118.

The monitor television 118 has a reference flat plate 1.
A situation is shown in which the spot image conjugate to the pinhole 104a from 07 matches the intersection of the crosshairs on the reticle plate 121.

a-4: Reference lens holder 109 having a reference lens 109 in the device lens barrel 108 of the interferometer
A is attached using a known holding means (not shown).

a-5: Attach the holder 500 to the reference lens holder 109 with the mounting screw 503 so that the reference surface 502 of the holder 500 having the adjustment mirror 501 contacts the reference surface 109b (see FIG. 15A) of the reference lens holder 109a.
Attach to a.

a-6: Place the autocollimator 510 on the optical bench 100, and as shown in FIG.
Mirror 5 for adjusting autocollimator 510
Directly face 01. Thereafter, this autocollimator 510 is fixed on the optical bench 100 so that it does not move.

a-7: Place the adjustment mirror 501 into the holder 50
0 from the reference lens holder 109a.

a-8: Known five-axis holder (not shown) (x,
The adjustment lens 520 held in the five axes of y, z, φ _A , φ _B ; φ _A and φ _B indicate horizontal and vertical tilt directions) is placed between the reference lens 109 and the autocollimator 510 . Place it in At this time, as shown in FIG. 15A, the adjustment lens 520 has a center of curvature Q ₁ of the spherical surface 521 for generating the spherical wave 520a of the adjustment lens 520, which coincides with the focal point F of the reference lens 109, and The plane 522 of the lens is arranged perpendicular to the optical axis O ₅ of the autocollimator.

The adjustment lens 520 is set so that the interference fringes between the reference light from the reference plane plate 107 projected on the monitor television 118 and the object light (spherical wave) from the spherical surface 521 of the adjustment lens 520 are made to be one color. Then, the target image 51 is determined using the autocollimator's eyepiece observation image.
1 and the reticle image 512a, precise positioning is performed.

(Setting the hologram standard for adjustment) a-9: Aspherical wave 52 of the adjustment lens 520
When the aspherical surface 523 for generating 3a is located at the above-mentioned setting completion position, the object light from this aspherical surface 523 and the reference flat plate 10
An adjustment hologram prototype consisting of an interference pattern generated by interference with the reference light from 7, or a computer-generated hologram created by calculating such an interference pattern with a computer and using the electron beam writing method based on the calculation results. The hologram prototype for adjustment is vacuum-adsorbed onto the XY direction moving stage 211 of the hologram prototype holder 200 described above.

a-10: Switch the changeover switch 124,
The image of the TV camera 117 of the interference fringe observation optical system is displayed on the monitor TV 118.

a-11: Adjust the feed screws 208, 216, 217, and 218 to separate the object light (aspherical wave) from the aspherical surface 523 of the adjusting lens 520 into, for example, the first-order diffracted light by the adjusting hologram prototype, and the reference plane. The interference fringes in the spatial filter 113 with, for example, the 0th order diffracted light of the reference light from the face plate 107 are made to be one color. As a result, the adjustment hologram prototype was adjusted in the X, Y, Z, and θ directions, and positioning was completed.

(Setting the hologram prototype for measurement) a-12: Adjust the reticle moving knob (not shown) and place it on the alignment mark 306 of the hologram prototype for adjustment that was positioned in step (a-11) above, as shown in FIG. As shown in the example of the observation field of the eyepiece 259, the reticle plates 257, 2
58 circular indicators 260 and 261 are matched.

a-13: Just in case, autocollimator 51
0 and reconfirms whether the target image 511 and the reticle index 512a match, that is, whether the adjusting lens 520 is correctly positioned.

If the position is correct, step (a)
It is determined that the settings from -9) to (a-12) have been performed correctly, and the autocollimator 510 and adjustment lens 520 are unnecessary after this, so they are removed.

a-14: Stage 2 hologram prototype for adjustment
11, and instead, the measurement hologram prototype 300 is placed on the stage 211 and vacuum-adsorbed.

a-15: While looking through the eyepiece lens 259 of the hologram prototype holder, follow the step (a-15).
12) Reticles 257, 25 positioned
8 circular indicators 260, 261 and step (a
-14) Measurement hologram prototype 3 mounted on
The feed screws 216, 217, and 218 are adjusted so that the hologram prototype is aligned with the alignment mark 306 of 00, and the hologram prototype is moved and positioned together with the stage 211.

(Setting the test object) a-16: Set the test object T in a known 6-axis holder (x, y, z, θ _A , θ _B , θ 6 axes: θ is rotation around the optical axis). do.

a-17: Switch the changeover switch 124 to the television camera 12 of the alignment optical system 125.
3 is displayed on a monitor television 118. The object T is held so that the first-order diffracted spot light (usually brighter than the 0th-order diffracted light) from the test surface matches the crosshair image of the reticle plate 121 on the screen of the monitor television 118 and becomes the smallest spot. Adjust the holder.

a-18: Next, switch the changeover switch 124 to turn on the television camera 117 of the interference fringe observation optical system.
The video is sent to the monitor television 118. As a result, the interference fringes are displayed on the monitor television 118, and the holder is finely adjusted so that the direction and pitch of the interference fringes are suitable for measurement.

b. Setup for off-axis measurement type In the case of off-axis measurement type, the work of adjusting the inclination of the reference flat plate 107 is simply added to the above-mentioned on-axis measurement. This tilting operation of the reference plane plate 107 is performed between step (a-15) and step (a-16) of the on-axis setup step described above, that is, after the setting of the hologram prototype for measurement is completed. This work of tilting the reference flat plate is carried out in the following steps.

b-1: Off-axis adjustment microscope 410
is placed in front of the scale 401 of the pinhole reticle 104 near a position corresponding to the scale number of the desired off-axis angle, as shown by the two-dot chain line in FIG. Next, the eyepiece lens 41
5, position the microscope so that the scale line of the desired off-axis angle, for example, 2.5°, is in the center of the field of view.

b-2: Tilt the reference plane plate 107 so that the reflection spot S is aligned with the desired graduation line (e.g.
2.5° scale line). When the tilt adjustment of the reference plane plate 107 is completed, the microscope 410 is removed.

b-3: Switch the changeover switch 124 to turn on the television camera 12 of the alignment optical system 125.
3 is displayed on the monitor television 118. And this monitor TV 11
The micro mechanism 13
0 to rotate the optical bench 130
Rotate around the LD.

Modification of the embodiment (1) Instead of the reference plane plate 107, the reference lens 10
You may use the rearmost surface of 9. In this case, this reference lens can be tilted or decentered to perform off-axis measurements.

(2) Instead of the scale 401 of the pinhole reticle 104 for off-axis angle checking,
As shown in FIG. 16, line sensor 601
Alternatively, the off-axis angle may be adjusted by directly receiving light at the spot S and detecting the off-axis angle from the position of the light-receiving element.

(3) There are many possible variations of the alignment mark 306 and alignment optical system 250 for setting the hologram prototype 300, some of which will be briefly described below.

(3-1) In the example shown in FIG. 17, the image of the alignment mark 306 by the objective lens 240 is directly received by the area sensor 602, its position is stored as element address information, and the alignment of the measurement hologram prototype is performed. Adjust so that the marks are located at the same element address.

(3-2) In the example shown in FIG. 18, a hollow circular mark 606 is used as the alignment mark of the hologram prototype 300, and this circular mark 606 and a negative/positive A related black circle mark 607 is arranged, followed by a light receiving element 608. As a result, the circular mark 606 of the hologram prototype 300
and black circle mark 60 on reticle 257, 258
After setting the hologram standard for adjustment so that the output from the light receiving element 608 becomes zero, the reticles 257 and 258 are moved. The subsequent setting of the measurement hologram prototype is similarly adjusted so that the output from the light receiving element 608 becomes zero.

(3-3) Figure 19A shows the hologram prototype 30
0 alignment mark 306, a fine first concentric mark 609 is provided, and a second concentric mark 609 having the same shape as the first concentric mark 609 is provided.
A concentric circle mark 610 is installed, for example, on the Z-axis movement stage 205 in front of the objective lens 240 and very close to the X-Y direction movement stage 211 so as to be movable within a plane perpendicular to the optical axis of the objective lens 240. shows. This second
Reference plate 608 with concentric marks 610
is moved so that moire fringes 611 (see FIG. 19B) caused by both marks 609 and 610 disappear. Reference plate 6 at this time
Using the adjustment position 08 as a reference, the measurement hologram prototype is positioned so that moire fringes between the first concentric circle mark of the measurement hologram prototype and the second concentric circle mark of the reference plate do not appear.

(3-4) In the example shown in FIG. 20, instead of the alignment mark of the hologram prototype 300, it is configured with a Fresnel lens 620. In other words, the light from the light source is divided into four by the detector 621.
The detector 621 is moved so that the output from each split element surface is equal, that is, the center of the detector 621 and the optical axis of the Fresnel lens 620 match, and the moving position is used as the reference position for measurement. Set up the hologram prototype.

Note that if the Fresnel lens 620 is provided with astigmatism, the deviation of the hologram prototype in the Z-axis, that is, the optical axis direction can also be adjusted by the output difference from each divided element surface of the detector 621.

(4) In setting the adjustment hologram prototype, instead of using the adjustment lens 520 having a spherical surface 521 and an aspheric surface 523, the 21st A.
As shown in FIG. 21B, an adjustment lens 650 having only a spherical surface 521 is used.

That is, first, the above-mentioned step (a-3)
Then execute step (a-8) to obtain the spherical surface 52.
₁ and the focal point F of the reference lens 109
The adjustment lens 65 is aligned so that the plane 522 is perpendicular to the collimator optical axis _O5 .
Set to 0. Next, the adjustment lens 650 is moved backward (or advanced) by a predetermined distance D, as shown in FIG. 21B. As a result, the reflected wavefront from the spherical surface 522 is not a perfect spherical wave, but has an aberration, in other words, it is emitted as an aspherical wave. If the hologram prototype for adjustment is created as an interference pattern between this aspherical wave and the reference light from the reference plane plate, the 21st B.
After moving the adjustment lens 650 as shown in the figure, by performing the steps (a-9) to (a-11) described above using the adjustment hologram prototype, the adjustment hologram prototype can be adjusted. The device can be set correctly, and in turn, the hologram prototype for measurement can be set correctly by steps (a-12) to (a-15).

(5) Although the hologram pattern 301 of the hologram prototype 300 detailed based on FIGS. 2 and 4 is an amplitude-type hologram pattern, the present invention is not limited to this, and the hologram pattern You may also use

[Brief explanation of the drawing]

Fig. 1 is an optical layout diagram showing the entire holographic interferometer according to the present invention, Fig. 2 is a plan view showing the configuration of the hologram prototype, and Fig. 3 is a black-white ratio inspection pattern applied to the hologram prototype. FIG. 4 is a diagram showing an example of a hologram pattern in its first quadrant, FIG. 5 is a front view showing a hologram prototype holder, and FIG. 6 is a diagram showing the configuration of FIG.
7 is a cross-sectional view of FIG. 5,
Fig. 8 is a perspective optical layout diagram showing the alignment optical system of the hologram prototype holder, Fig. 9 is a diagram showing an example of the ocular field of view of the alignment optical system of the hologram prototype holder, and Figs. 10A to 10C are the hologram prototype holder. A schematic diagram showing the function of the instrument holder, Figure 11 is a partial diagram showing the optical arrangement relationship for on-axis measurement and off-axis measurement, Figure 12 is a diagram showing an example of a pinhole reticle, and Figure 13 is for off-axis adjustment. Optical layout diagram showing the configuration of the microscope, 1st
Figure 4 is an optical layout diagram showing the configuration of a microscope for on-axis adjustment, and Figure 15A is an illustration of the reference lens, adjustment mirror, adjustment lens, and autocollimator to explain the setting adjustment of the holographic interferometer of the present invention. Diagram showing the placement relationship of the four parties, 1st
Figure 5B is a diagram showing an example of the eyepiece observation field of an autocollimator, Figure 16 is an optical layout diagram showing a modification of the pinhole reticle, and Figures 17 to 20 are the alignment marks and alignment of the hologram prototype, respectively. Diagram 21A showing a modification of the optical system
21B and 21B are diagrams showing another setting method of the hologram prototype for adjustment, and FIG. 22 is an optical layout diagram of a conventional Fizeau type interferometer. 101...Laser, 104...Pinhole reticle, 106...Collimator lens, 107
...Reference plane plate, 109...Reference lens, T...
Test object, 110...Beam splitter, 113...
... Spatial filter, 117, 123 ... Television camera, 200 ... Hologram prototype holder, 20
5...Z-axis direction movement stage, 211...X-Y
Directional movement stage, 208, 216, 217, 2
18...Feed screw, 223, 232, 233...
Elastic body, 215... Spring, 240... Objective lens, 300... Hologram prototype, 301...
Hologram pattern, 302...Distortion inspection pattern, 306...Alignment mark, 303...Black and white ratio inspection pattern, 410...Microscope for off-axis adjustment, 420...Microscope for on-axis adjustment,
501... Adjustment mirror, 520, 650... Adjustment lens, 510... Autocollimator.

Claims (1)

[Scope of Claims] 1. A light source, a collimator lens for projecting the light from the light source onto an object as a parallel beam, and an optical surface for generating a reference wavefront disposed behind the collimator lens; A holographic interference device comprising a hologram prototype that diffracts at least one of a reflected light wavefront from the object to be inspected and a reference wavefront from the reference wavefront generation optical surface, and means for switching between an on-axis method and an off-axis method. It is a total,
In order to set the incident angle of the reference wavefront required for the hologram prototype, the hologram prototype includes monitoring means for monitoring the intersection angle between the reference wavefront generation optical surface and the optical axis of the collimator lens. A holographic interferometer. 2. The light source includes a laser light source, a condensing lens that condenses light from the laser light source, and is arranged at a focal position of the condensing lens to select light from the condensing lens and use it as a secondary light source. 2. A hologram according to claim 1, wherein the holographic device comprises a pinhole, and the monitoring means monitors the imaging position of a reflected image of the pinhole on the optical surface for generating a reference wavefront. Itsuku interferometer. 3. The reference wavefront generating optical surface is rotatable about an axis perpendicular to the optical axis of the collimator, and the monitoring means is configured to rotate within a plane perpendicular to the optical axis of the collimator including the pinhole. 3. The holographic interferometer according to claim 2, wherein the holographic interferometer is a scale plate provided with a scale corresponding to the rotation angle of the optical surface and running in a direction perpendicular to the rotation axis. 4. The holographic interferometer according to claim 3, wherein the pinhole is integrally formed with the scale plate. 5. Claim 3 or 4, wherein the monitor means includes an off-axis microscope for magnifying and observing the reflected image projected onto the scale plate together with the scale. The holographic interferometer described in section. 6. The monitoring means includes an on-axis microscope arranged on the optical axis of the collimator lens to observe whether the reflected image is re-projected onto the pinhole. A holographic interferometer according to claim 2. 7. The holographic interferometer according to any one of claims 1 to 6, wherein the reference wavefront generating optical surface is a flat plate.