JPH0554601B2 - - 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. .

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. and the reference light,
A holographic interferometer is known that precisely measures the error of an aspherical optical element under test from a reference aspherical surface based on 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 the collimator lens C. Then, the imaging lens
A part of the light beam reflected by the beam splitter BS, which is a half mirror tilted between _L1 and the diverging lens _L2 , is diverged by the diverging lens _L2 and then reflected by the reference spherical surface R. It is reflected, passes through the same optical path as the incident light _l1 , passes through the beam splitter BS, the hologram prototype H, and the imaging lens _L1 , becomes 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.

By the way, conventional measurement methods using a holographic interferometer include an on-axis method and an off-axis method. The on-axis method is a method in which measurement is performed with the object light and reference light coaxial, while the off-axis method is a method in which the object light and reference light are measured non-coaxially, that is, the propagation axes of the object light and the reference light are tilted to each other. That is, it is a cross-type measurement method.

Problems to be Solved by the Invention The on-axis method has the advantage of being able to measure objects with large asphericity because the spatial frequency of the hologram prototype used can be lowered. On the other hand, all the diffracted lights from the 0th order to the higher orders by the hologram prototype are all superimposed on the optical axis, although their focal lengths are different. Even if it is placed at the focal point, some of the higher-order diffracted light such as the 0th order and 2nd order passes through this spatial filter, so the so-called "middle gap", which is the central part centered on the optical axis of the object, is measured. The drawback was that I couldn't do it.

On the other hand, the off-axis method does not have the problem of hollow spots like the on-axis method, but because the spatial frequency of the hologram prototype used for measurement is high, the asphericity may be affected due to constraints on the production and alignment of the hologram prototype. Only small test objects can be measured.

Furthermore, the off-axis angle (the angle formed by the mutual propagation axes of the object beam and the reference beam) varies depending on the type of test object and the degree of asphericity, so when creating a hologram prototype, the optimal off-axis angle for each test object is determined in advance. The off-axis angle can be determined. Moreover, because the off-axis angle of conventional interferometers for off-axis methods is fixed, there are drawbacks such as the inability to use hologram prototypes with different off-axis angles and the limitations on the objects that can be measured. It was hot.

Furthermore, conventional holographic interferometers cannot perform both on-axis and off-axis measurements.

OBJECTS OF THE INVENTION The present invention has been made in view of the drawbacks of the conventional holographic interferometers, and its first object is to provide a holographic interferometer capable of both on-axis and off-axis measurements. It is about providing.

The second object of the present invention is that the off-axis angle can be set arbitrarily, and hologram prototypes with various off-axis angles can be used.Therefore, there are fewer restrictions on the type and asphericity of the test object, and the measurement range is Our objective is to provide a wide range of holographic interferometers.

Configuration of the Present Invention The present invention includes a collimator lens for projecting light from a light source onto a test object as a parallel beam, and a collimator lens disposed on the exit side of the collimator lens for projecting a portion of the light from the collimator lens. a reference light generating optical element for reflecting to produce a reference light; and a collimator disposed on the incident side of the reference light generating optical element for reflecting the object light from the test object and the reference light. a beam splitter tilted to the optical axis of the lens; a hologram prototype placed on the reflection optical axis of the beam splitter; and either the object beam or the reference beam diffracted by the hologram prototype. A holographic interferometer comprising an observation optical system for observing interference fringes between one light wave and the other light wave, wherein the reference light generating optical element is tiltable with respect to the optical axis of the collimator lens. and the observation optical system can be rotated at any angle with a rotation center at a position on the optical axis of the imaging lens of the observation optical system and substantially conjugate with the exit pupil center of the collimator lens. This is a holographic interferometer featuring:

Effects of the Invention According to the holographic interferometer of the present application having the above configuration, the optical element for generating the reference light and the optical system for observing interference fringes can be set at any angle, so that both the on-axis method and the off-axis method can be used. To provide a holographic interferometer which not only allows measurement but also has a wide measurable area with fewer restrictions on the type of object to be measured and the degree of asphericity because the off-axis angle can be set freely. Furthermore, the holographic interferometer of the present invention has the advantage that hologram prototypes with different off-axis angles can be used in common.

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 device optical axis (collimator optical axis) ₀₁ . 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 110 between the pinhole reticle plate 104 and the collimator lens 106.
a is incident on a prism type beam splitter 110 tilted with respect to the optical axis _O1 . Both the object beam and the reference beam 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 an imaging lens 122, and the switching circuit 12
4 on the monitor 118. These reticle plate 121, imaging 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, imaging lens 122, TV camera 11
7, 123 and the camera 120 are the optical bench 13
0. This optical bench 130 is located at a point LC on the optical axis of the imaging lens 111, which is conjugate with the exit pupil EP of the combined optical system of the collimator lens 106 and the reference lens 109, for off-axis angle adjustment to be described later. Micro feed mechanism 13
The arm 131 is fixed to the arm 131, which rotates when driven by the arm 131. Note that if the object to be inspected is a flat object, the reference lens 109 is not necessary; in this case, the center of rotation is
LC is located at a position conjugate with the exit pupil center of the collimator lens 106.

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. Therefore, as shown in FIG. 4, the pattern calculation and drawing data calculation are performed as follows:
This is done only for the first quadrant of , and the other (-x, y),
For the second, third, and fourth quadrants of (-x, -y), (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, the data can be more accurate.

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

At the same time, the stage 211
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 254, 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 movements in X, Y, and θ can be performed on one stage without using a triple stage structure of a directional movement stage and a θ rotation stage. Further, the configuration thereof is extremely simple, and 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 object to be measured and the reference light from the reference plane are coaxial, and the spatial frequency of the hologram prototype used for measurement can be lowered, making it possible to measure objects with large degrees 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 off-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 tan β=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 or-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: Transmitted through the half mirror 421 of the microscope 420 and made into the pinhole 1 by the condensing lens 103
It is observed through the eyepiece lens 415 whether the reflected spot image S of the light beam condensed on the pinhole 104a by the reference plane plate 107 is again formed on the pinhole 104a.

The spot light is observed by the eyepiece lens 415 only when the spot S coincides with the pinhole 104a. Eyepiece lens 415
The reference plane plate 107 is adjusted so that the spot S can be observed through it. 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 12 of the alignment optical system 125.
3 so that the images are displayed on the monitor television 118.

A situation is displayed on the monitor television 118 in which the spot image conjugate to the pinhole 104a from the reference plane plate 107 matches the intersection of the crosshairs on the reticle plate 121.

a-4: Reference lens holder 10 having a reference lens 109 in the device lens barrel 108 of the interferometer
9a is attached using a known holding means (not shown).

a-5: The reference surface 502 of the holder 500 having the adjustment mirror 501 is the reference surface 109b (first
5A)), attach the holder 500 to the reference lens holder 109a with a mounting screw 503.

a-6: Place the autocollimator 510 on the optical bench 100, and adjust the autocollimator 510 so that the crosshair target 511 matches the circle indication 512a of the reticle 512, as shown in FIG. 15B. Directly face the mirror 501. 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 500
Remove the entire reference lens holder 109a 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.
coincides with the focal point F of the reference lens 109,
In addition, the adjustment lens is arranged so that its plane 522 is perpendicular to the optical axis _O5 of the autocollimator.

This setting of the adjustment lens 520 is performed so that the interference fringes between the reference light from the reference flat plate 107 projected on the monitor television 118 and the object light (spherical wave) from the spherical surface 521 of the adjustment lens 520 become one color. Rough positioning is performed using the autocollimator, and then precise positioning is performed by matching the target image 511 and the reticle image 512a using the ocular observation image of the autocollimator.

(Setting of adjustment hologram prototype) a-9: Aspherical wave 523 of adjustment lens 520
When the aspherical surface 523 for generating a is located at the above-mentioned setting completion position, an adjustment hologram consisting of an interference pattern generated by interference between the object light from the aspherical surface 523 and the reference light from the reference plane plate 107 is created. A prototype or such an interference pattern is calculated by a computer,
An adjustment hologram prototype consisting of a computer-generated hologram created by electron beam lithography based on the calculation result 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 so that 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 remove the adjustment lens 520.
The interference fringes in the spatial filter 113 between, for example, the 1st-order diffracted light from the hologram prototype for adjustment of the object light (aspherical wave) from the aspherical surface 523 and the 0th-order diffracted light of the reference light from the reference plane plate 107 are in a monochromatic state. so that it becomes 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 movement 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 shown in FIG.
Match 261.

a-13: Just in case, autocollimator 510
Check whether the target image 511 matches the reticle index 512a.
That is, it is reconfirmed whether the adjustment lens 520 is maintained in the correctly positioned state.

If the positioning is correct, it is determined that the setting in steps (a-9) to (a-12) has been performed correctly, and the autocollimator 510 and adjustment lens 520 are unnecessary after this and are removed.

a-14: The hologram prototype for adjustment is placed on stage 21
1, and instead, the measurement hologram prototype 300 is placed on the stage 211 and vacuum-adsorbed.

a-15: Step (a) while looking through the eyepiece 259 of the hologram prototype holder.
-12) reticle 25 positioned
Turn the feed screw 21 so that the circular indicators 260, 261 of 7,258 and the alignment mark 306 of the measurement hologram prototype 300 placed in step (a-14) match.
6, 217, and 218 to move and position the hologram prototype together with the stage 211.

(Setting the test object) a-16: Place the test object T in a known 6-axis holder (x,
Six axes: y, z, φ _A , φ _B , and θ (θ is rotation around the optical axis) are set.

a-17: Switch the changeover switch 124 to set the TV camera 1 of the alignment optical system 125.
The video from 23 is displayed on a monitor television 118. The first-order diffracted spot light (usually brighter than the 0th-order diffracted light) from the test surface is matched with the crosshair image of the reticle plate 121 on the screen of the monitor television 118, and is made into the smallest spot.
Adjust the holder that holds the test object T.

a-18: Next, switch the changeover switch 124 to turn on the television camera 1 of the interference fringe observation optical system.
17 is sent to a monitor television 118. This allows monitor TV 1
The interference fringes are projected onto 18, 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, in addition to the above-mentioned on-axis measurement, the reference flat plate 10
Only 7 inclination adjustment operations are added. 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,
As shown by the two-dot chain line in FIG. 1, it 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. Next, while looking through the eyepiece 415, the microscope is positioned so that the scale line of the desired off-axis angle, for example, 2.5 degrees, is at the center of the field of view.

b-2: Tilt the reference plane plate 107 so that the resulting reflection spot S coincides with the intersection of a desired scale line (for example, a 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 and set the TV camera 1 of the alignment optical system 125.
23 is displayed on a monitor television 118. Then, the reference plane plate 1 is placed on the intersection of the crosshairs of the reticle 121 displayed on the monitor television 118.
The optical bench 130 is rotated around the rotation center LD by operating the micro mechanism 130 so that the reflected spot images from 07 coincide with each other.

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 alignment mark 30
The image by the objective lens 240 of No. 6 is directly received by the area sensor 602, its position is stored as element address information, and adjustment is made so that the alignment mark of the measurement hologram prototype is located at the same element address.

(3-2) The example shown in Figure 18 is the hologram prototype 30
The hollow circular mark 606 is used as the alignment mark for the alignment optical system 2.
50 reticle plates 257, 258 are arranged with a black circle mark 607 having a negative/positive relationship with this circular mark 606, and a light receiving element 608 is arranged after that. As a result, the circular mark 606 on the hologram prototype 300 and the black circle mark 607 on the reticles 257, 258 are aligned, and the light receiving element 608
After setting the adjustment hologram prototype so that the output from the reticle 2 is zero,
Move 57,258. 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) FIG. 19A shows a detailed first mark instead of the position mark 306 of the hologram prototype 300.
A concentric circle mark 609 is provided, and a second concentric circle mark 609 having the same shape as this first concentric circle 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.
The reference plate 608 having the second concentric mark 610 is moved so that the moire fringes 611 (see FIG. 19B) caused by both marks 609 and 610 disappear. Using the adjusted position of the reference plate 608 at this time as a reference, the measurement hologram prototype is positioned so that moire fringes between the first concentric circle mark on the measurement hologram prototype and the second concentric circle mark on the reference plate do not appear. do.

(3-4) The example shown in Figure 20 is the hologram prototype 30
Instead of the zero alignment mark, it is constructed with a Fresnel lens 620. That is,
The light from the light source is received by the 4-split detector 621, and 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 coincide. Using the movement position as the reference position, set up the hologram prototype for measurement.

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 drawings]

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 a diagram showing the reference lens, adjustment mirror, adjustment lens, and autocollimator for explaining the setting adjustment of the holographic interferometer of the present invention. Diagram showing the placement relationship of the four parties, No. 15
Figure B shows 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 show the positioning marks and alignment of the hologram prototype, respectively. FIGS. 21A and 21B are diagrams showing a modification of the optical system, and FIGS. 21A and 21B are diagrams showing another setting method for the adjustment hologram prototype, and FIG. 22 is an optical layout diagram of a conventional Fizeau type interferometer. DESCRIPTION OF SYMBOLS 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...TV camera, 200...Hologram prototype holder, 205...Z-axis direction movement stage, 211...X-Y direction movement stage, 208,
216, 217, 218...Feed screw, 223, 2
32, 233...Elastic body, 215...Spring, 2
40...Objective lens, 300...Hologram prototype, 3
01...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 collimator lens for projecting light from a light source onto a test object as a parallel beam of light, and a collimator lens disposed on the exit side of the collimator lens to reflect a part of the light from the collimator lens. a reference light generating optical element for generating a reference light, and a collimator lens disposed on the incident side of the reference light generating optical element for reflecting the object light from the test object and the reference light. a beam splitter tilted to the optical axis of the beam splitter, a hologram prototype placed on the reflection optical axis of the beam splitter, and either the object beam or the reference beam diffracted by the hologram prototype. A holographic interferometer includes an observation optical system for observing interference fringes between one light wave and another light wave, wherein the reference light generating optical element is tiltable with respect to the optical axis of the collimator lens. , and the observation optical system can be rotated to any angle with a rotation center located on the optical axis of the imaging lens of the observation optical system and approximately conjugate with the exit pupil center of the collimator lens. Features a holographic interferometer. 2. The reference light generating optical element has a reference lens on its exit side for once converting the light from the collimator lens into a spherical wave and projecting it onto the test object, and the observation optical system is configured to generate the reference light. 2. The holographic interferometer according to claim 1, wherein the holographic interferometer is rotatable about a position that is substantially conjugate with the center of a composite exit pupil of the lens and the collimator lens. 3. The holographic interferometer according to claim 1 or 2, wherein the beam splitter is arranged on the incident side of the collimator lens. 4. The reference light generating optical element has a front plane,
The collimator lens is composed of two surfaces, a rear plane inclined at a slight angle with respect to the front plane, and one of the planes reflects a part of the light from the collimator lens and uses it as a reference light. A holographic interferometer according to any one of ranges 1 to 3.