JPS6244605A - Holographic interferometer - Google Patents

Abstract

PURPOSE:To obtain a holographic interferometer which has a wide measurement range by allowing an optical element for reference light generation to slant to the optical axis of a collimator lens and allowing an optical observation system to swivel almost around the exit pupil of the collimator lens as a center of swiveling by an optional angle. CONSTITUTION:The collimator lens 106 collimates light from a light source 101 into parallel luminous flux and protects it on a body T to be detected, the optical element 107 reflects part of the light from the collimator to generate reference light, and a beam splitter 110 is provided on the incidence side of the element 107 slantingly to the optical axis of the collimator lens 106 to reflect the object light from the object body T and reflected light. Then, a hologram primary standard 300 is arranged on the optical axis of reflection of the splitter 110 and the optical observation system 119 is used to observe interference fringes between the object light and reference light which are diffracted by it. The optical element 107 is provided slantingly to the optical axis of the lens 106 and the optical observation system 119 is allowed to swivel almost around the exit pupil of the lens 106 as the center of swiveling by an optional angle.

Description

[Detailed description of the invention] The present invention is a holographic interference method for precisely measuring the surface shape of optical elements such as lenses and mirrors, especially aspherical optical elements, using a hologram prototype. Regarding the meter.

As a method for measuring the surface shape of an aspherical optical element, a hologram prototype created by interference of a reference light wavefront with a reflected or transmitted wavefront from a reference aspherical surface or an optical design 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 planning method, etc., is used as a hologram prototype, and the hologram prototype of the reflected or transmitted wavefront from the aspherical optical element under test is used as a hologram prototype. A holographic interferometer is known that allows diffracted light by a reference light to interfere with a reference light, and accurately measures the error of a test aspheric optical element from a reference aspheric surface based on the amount and shape of interference fringes.

Further, as an interferometer, for example, a Fizeau type interferometer shown in FIG. 22 is known. i.e. light source (laser)
The light from the LS is made into a parallel beam by a collimator lens C. After that, the imaging lens L.

A part of the light beam reflected by the beam subrick BS consisting of a half mirror tilted between the diverging lens L2 and the diverging lens L2 is reflected by the reference spherical surface R, and the incident light is Through the same optical path as (1,), beam splitter BS, hologram prototype ■], imaging lens L,
The light 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 splinter BS. The 0th-order light that passes through the beam splitter BS and is not diffracted by the hologram prototype is cut by the spatial filter SF, while the -order diffracted light, for example, which is diffracted by the hologram prototype, passes through the aperture of the spatial filter SF and is 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 beam and reference beam coaxial, while the off-axis method is a method in which the object beam and reference beam are not coaxial, that is, the propagation axis of the object beam and the propagation axis of the reference beam are mutual. This is a type of measurement method that slopes or intersects.

The problem that Zero Hatsuhi is trying to solve The on-axis method has the advantage of being able to measure objects with large degrees of asphericity because the spatial frequency of the hologram prototype used can be lowered. On the other hand, since 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, for example, the -order diffracted light is extracted. Even if a spatial filter is placed at the focal point of the first-order diffracted light, some of the higher-order diffracted light, such as the zeroth and second-order diffracted light, passes through this spatial filter, resulting in so-called "hollow" light from the object to be measured. There was a drawback that the central part around the axis could not be measured.

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 object being tested and the degree of asphericity.
When creating a bologram prototype, the optimal off-axis angle is determined for each object in advance. 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. Ta.

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

1 □ヱThe present invention was made to address the shortcomings of the conventional volographic ink interferometer, and its first purpose is to develop 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 of object to be measured and the degree of asphericity, and the measurement range can be increased. The object of the present invention is to provide a wide bolographic interferometer.

The structural features of the holographic interferometer of the present invention for achieving the above object include a collimator lens for projecting the light from the light source as a parallel beam onto the object to be measured;
Applicable? a reference light generation optical element disposed on the exit side of the collimator lens to reflect a part of the light from the collimator lens to produce a reference light; and a reference light generation optical element disposed on the incidence side of the reference light generation optical element. a beam splitter tilted to the optical axis of the collimator lens to reflect the object light from the test object and the reference light; a hologram prototype disposed on the reflection optical axis of the beam splitter; A bolographic interferometer comprising an observation optical system for observing interference fringes between the object light and the reference light diffracted by the hologram prototype, wherein the reference light generating optical element is the collimator lens. The observation optical system can be tilted with respect to the optical axis of the collimator lens, and the observation optical system can be rotated to any angle about the center of the exit pupil of the collimator lens.

According to the bolographic interferometer of the present application, which has a configuration that exceeds the effects of the invention, the optical element for generating the reference light and the optical system for observing interference fringes can be set at any angle, so that the on-axis method and the off-axis method can be used. The present invention provides a holographic interferometer that not only can perform both measurements, but also has a wide measurable area, with fewer restrictions on the type of object to be measured and the degree of asphericity, since the off-axis angle can be set freely. Furthermore, the holographic interferometer of the present application has the advantage that hologram prototypes with different off-axis angles can be used in common.

Embodiments of the holographic interferometer according to the present invention will be described in detail below.

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. A pinhole reticle plate 104 having a pinhole 104a is arranged near this focal point. The diverging light passing through the pinhole 104a acts as if the pinhole 104a were a secondary light source. Note that a quarter wavelength plate 105 is disposed between the mirrors 102a and 102b.

A collimator lens 106 has a focal point at the pinhole 10.
4a.

The pinhole 104 uses the pinhole 104a as a secondary light source.
The light beam emitted from a is made into a parallel light beam by the collimator lens 106. A reference plane plate 107 is arranged behind the collimator lens 106. This reference plane plate 107 is arranged so that the front plane 107a is perpendicular to the apparatus 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 has become.

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

Object light reflected from the test object T and reference light 1 reflected from the front plane 107a of the reference plane plate 107
What is ``Near Ho''grant'' board 104.: D Remeter 1
Between the lens 106 and the half mirror surface 1
) 0a is incident on the prism type beam splitter 1) 0 tilted with respect to the optical axis OI. Both the object light and the reference target are reflected by the half mirror 1) 0a, 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 wavelength plate 105. Pinhole reticle 104° zoom splitter 1) 0. Collimator lens 106° reference plane plate 107. 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 passes through the imaging lens 1)
1. Spatial filter 1) 3 via half mirror 1) 2
is imaged. This spatial filter 1) 3 is for selectively extracting only one of the reference light and object light that was diffracted by the hologram prototype 300 and the other light that was not diffracted by the hologram prototype 300. It is. To be more specific, as in the conventional Fizeau interferometer shown in FIG. Selectively extract only the 0th-order reference light and the 1st-order object light diffracted by the hologram prototype 300 using the object light from the test object T, and extract the 0th-order, 2nd-order and higher-order diffracted light of the reference light and the object light. The next diffracted light acts to be cut.

The object light and reference destination selected by spatial filter 1) 3 are:
Zoom lens 1) 4. An interference pattern between the reference light and the object light is formed on the imaging surface 1) 7a of the TV camera 1) 7 via the half mirror 1) 5 and the imaging lens 1) 6. The image taken by the TV camera 1) 7 is captured by an interference pattern analysis device 1) 9 consisting of a monitor TV 1) 8 and a personal computer.
sent to. Note that the reference light and object light transmitted through the half mirror 1) 5 are transferred to the film 12 of the instant development type camera 120.
When formed on the imaging surface 1) 7a, an interference pattern similar to that formed on the imaging surface 1) 7a is formed on the film 120a and recorded on the film 120a.

A part of the light passing through the imaging lens 1) 1 is sent to the half mirror 1.
) 2, and is imaged on a reticle plate 121 arranged with the crosshairs perpendicular to the optical axis.

The image on the reticle plate 121 is transmitted through the photographing lens 122 to the T
The image is captured by the V camera 123 and displayed on the monitor 1) 8 via the switching circuit 124. These reticle plates 121
．． Photographing lens 122. TV camera 123. Monitor 1)
8 forms an alignment optical system 125 for setting the object T in the measurement optical path.

Imaging lens 1) 1, 1) 6. Half mirror 1) 2゜1)
5. Spatial filter 1)3. Zoom lens 1) 4, photographing lens 122. TV camera 1) 7°123 and camera 1
20 is placed on the optical bench 130. ,! be placed. This optical bench 130 has an arm that rotates by driving a known micro-feeding mechanism 131 around a point LC that is conjugate with 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 if the object to be inspected is a flat object, the reference lens 109 is not necessary, and in this case, the rotation center 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.

Also, unlike conventional Fizeau interferometers, this interferometer uses a collimator lens and a pinhole as its beam splitter.
Since it is disposed in the diverging beam between 04a and 04a, the area of the half mirror surface can be reduced to about 174 mm compared to the conventional beam splitter in which a beam splitter is provided in the parallel beam by the collimator lens.

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 the calculation information and drawing information for drawing a hologram pattern. Furthermore, since the beam splitter has become smaller, its manufacturing accuracy can be significantly improved, and its manufacturing cost can also be reduced.

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

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 splinter, 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 pre-lifter 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 broken, so even in the case of an on-axis hologram prototype, the hologram pattern had to be calculated for all quadrants to obtain drawing data. However, in this holographic interferometer, the beam splitter 1)0 is a prism type beam splitter as mentioned above, so the symmetry with respect to the optical axis is preserved, and the hologram pattern of the on-axis Borodaram prototype is a concentric circle pattern. and point symmetry. Therefore, the pattern calculation and drawing data calculation are performed using (X, V
), 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, which reduces calculation costs and calculation time, and reduces drawing 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.

Furthermore, black-white ratio test patterns 3o3 are formed at two locations outside the distortion test pattern. This black-and-white ratio test pattern includes, for example, a black part 304 and a white part 305 as shown in FIG.
A checkerboard pattern is used in which the same area is alternately arranged in a plane.

This black-and-white ratio test pattern 303 is drawn at the same time as the hologram pattern 301 is drawn with an electron beam, so if the black-and-white ratio of this black-and-white ratio test pattern 303 is measured with a densitometer, the black-and-white ratio of the hologram pattern itself can be indirectly determined. can be known in detail.

At the four corners of the hologram prototype 30.0, crosshair-shaped alignment marks 306 are formed for positioning when the hologram prototype 300 is attached to the hologram prototype holder 200. 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 a hologram prototype boulder 200. Bearing 20 placed on optical henna 100
1,202 supports a shirt l-203 so as to be slidable in parallel to the optical axis 0z (see FIG. 1) direction. A moving stage 205 in the Z-axis direction (optical axis 02 direction) is fixed to the shaft 203 by screws 204° 204. A cylinder 206 is attached to the bearing 201, and a spring 207 is fitted into the cylinder 206. On the other hand, an X-axis feed screw 208 is screwed into the bearing 202 . This X-axis feed screw 20
8 cooperates with a 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.

An X-Y direction movement stage 21) is placed on the stage surface 205a of the Z-axis direction movement stage 205 via a steel ball 210. As shown in FIG. 6, screws 212 are installed on the back side of the stage 21), and the openings 2 formed in the Z-axis moving stage 205
A spring 215 is hung between it and a rod 214 that is passed to the rear of the holder 13. The tensile force of the spring 215 pulls the X-Y direction moving stage 21) toward the stage surface 205a of the Z-axis direction moving stage 205, thereby stabilizing the moving surface.

Furthermore, as shown in FIG. 5, the Z-axis moving stage 205 is provided with two Y-axis threads 216 and 217 and one X-transport thread 218. The side surface of the X-Y direction moving stage 21) has guides 220 via bearings 219, and these guides 220 are connected to steel balls 22.
1 by feed screws 216, 217, and 218.

' The X-Y direction moving stage 21) further has a notch 222 on the side opposite to the mounting position of the X-axis feed screw 218. Side surface of notch 222 and Z-axis direction movement stage 2
A resilient body 223 is inserted between the upright piece 224 of 05.

As shown in FIG.
, a piston 226 inserted into the cylinder, and a spring 227 fitted into the cylinder 225 to constantly apply a pressing force to the piston 226.

Similarly, the stage 21) has notches 228 and 229 formed opposite to the Y transport line screws 216 and 217, and an elastic body 232° between the upright pieces 230 and 231 of the stage 205 and the side surfaces of these notches. 233 is interposed.

The configuration of the elastic bodies 232 and 233 is similar to 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 21) obtains a movement amount Y as shown in FIG. 10B. Also, by feeding the feed screw 218, the stage 2
1) obtains the amount of movement X as shown in FIG. 10A. Furthermore, the feed screws 216 and 218 are fixed, and the feed screw 217
By feeding only the stage 21), the stage 21) is rotated by a rotation angle θ, as shown in FIG. 10C.

The X-Y direction moving stage 21) has a substantially rectangular opening 235 at its center, and circular openings 236 at the upper left corner and lower right corner.
, 237 are formed. These circular openings 236.2
37 is an opening 2 formed in the Z-axis direction movement stage 205
It corresponds to 38.

The opening 238 includes a microscope objective lens 240 for observing the alignment mark 304 on the hologram prototype 300.
is inserted.

A circular groove 241 is formed around the opening 235 of the stage 21), and a nozzle 242 of a vacuum pump (not shown) is connected to this groove via a pipe 243. Furthermore, a guide piece 244 is provided on the outer surface of the stage 21).
is fixed.

As a result, the hologram prototype 300 is placed 1) 71) on the stage 21) along the guide piece and placed in the groove 241 with a vacuum pump.
By absorbing the air inside, it is brought into close contact with the stage 21) at atmospheric pressure.

Arms 246° 247 are attached to the tip of the shaft 203 and the tip of the ball 245 implanted in the stage 205, and a light emitting diode 248 and a heat ray absorption filter 249 are housed at the tips of the arms 246° 247, respectively. It is used to illuminate the alignment mark 304 of the hologram prototype placed on the stage 21).

Figure 8 shows hologram prototype holder-2 having the above-mentioned configuration.
00 is a perspective view schematically showing a hologram prototype alignment optical system 250 attached to the hologram prototype alignment optical system 250. The alignment optical system 250 includes the above-mentioned light emitting diode 248. Heat ray absorption filter 249° Objective lens 240. mirror 25
1 and a beam splitter 252.
and a light emitting diode 248. Heat ray absorption filter 249
．． Objective lens 240. It is composed of a second optical path 255 consisting of a mirror 254 and a beam splitter 252, and an eyepiece optical path 256 which is composed of the first optical path 253 and the beam splitter 252 of the second optical path 255.

This eyepiece optical path 256 includes reticle plates 257, 258 and an eyepiece lens 259 that move in a plane (xy plane) perpendicular to the optical axis 03 by a known moving means (not shown). ) °7′°″<t &
')? ! P1*) melt 260, 2617″
has been completed.

As described above, according to the present hologram prototype holder, it is possible to move these X, Y, and θ-related stages without using a triple stage structure of an X-direction moving stage, a Y-direction moving stage, and a θ rotation stage as in the past. can be performed in one stage. Further, the configuration thereof is extremely simple, and has the advantage of allowing highly accurate movement control and positioning.

D. Off-axis measurement Measurement methods using device 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. But 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, even if a spatial filter is placed at the focal point to extract the -order diffracted light, the 0th and 2nd order
A portion of the higher order diffracted light is also passed 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, the off-axis type does not have the unmeasurable part like the above-mentioned on-axis type, but the hologram is smaller than the on-axis type. Since the spatial frequency of the prototype becomes high, it is only possible to measure, for example, an aspherical object with a small degree of asphericity due to constraints on the production and alignment of the hologram prototype.

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.

Figure 1) is an optical layout diagram schematically showing on-axis measurement and off-axis measurement. In the case of on-axis measurement, the reference plane plate 107 is arranged perpendicular to the optical axis oI of the collimator lens 106.

Observation optical system, ie, spatial filter, for observing the interference pattern between the object light and the reference light 1) 3. Zoom lens 1)
4. The imaging lens 1) 6 and the image pickup tube 1) 7 are aligned with the optical axis 0.
The optical axis 02 is arranged perpendicularly to the optical axis 02.

A spatial filter 1) 3 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. The interference fringes will be imaged or photographed with an image pickup tube.

On the other hand, for off-axis measurements, as shown by the dashed line,
The reference plane 107 is rotated by an angle α (this angle α is referred to as an off-axis angle), and 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 defined as (where 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 are filtered through the spatial filter 1).
3' (referring to spatial filter 1) 3 during off-axis), and is configured so that both interference fringes can be observed and imaged.

The off-axis angle α is the half mirror surface 1) 0a of the beam splitter 1) 0 of the reflected light (reference light) from the reference plane.
can be determined from the imaging position of the image S formed on the pinhole reticle 104. That is, the amount of deviation between the imaging position and the optical axis O5 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 104 is provided at one end of the reticle 104.
a is formed, and a scale 401 is formed along the longitudinal direction from there to the other end side. The scale 401 is graduated according to the amount of deviation of the spot S corresponding to the off-axis angle α from the optical axis 0 I (the center of the pinhole 104a), and scale numbers 402 of the off-axis angle are printed below the 1 scale. It is.

FIG. 13 is a diagram showing the optical arrangement of an off-axis angle adjustment microscope 410 used when setting the off-axis angle α. The microscope 410 has an objective lens 41),
The light from the scale 401 and off-axis angle scale numbers 402 on the reticle 104 is made into parallel light, and the mirror 412
After being reflected by the lens, the image is formed on the aperture 414 by the 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 angle adjustment w4 micromirror 420. 1 Microscope for off-axis angle adjustment mentioned above 4
The difference in configuration from No. 10 is that the mirror 412 is a half mirror.
421, and there is no objective lens 41), and the condensing lens 103 of the interferometer 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 plane plate 107, and the spot S is projected with a vertical deviation from the scale 401, the surface of the reference plane plate 107 may be tilted or , optical axis 0
Since it can be determined that one rotation has occurred, these changes can also be made.

(On-axis arrangement of measurement optical system) a- The on-axis adjustment microscope 420 is set on the optical axis O2 of the collimator lens 106, as shown by the two-dot chain line in FIG.

a-2=Whether or not the reflected spot image S by the reference flat plate 107 of the light beam transmitted through the half mirror 421 of the microscope 420 and condensed onto the pinhole 104a by the condensing lens 103 is again imaged onto the pinhole 104a. is observed through the eyepiece 415.

Only when the spot S coincides with the pinhole 104a is the spot light observed through the eyepiece 415 degrees. The reference plane plate 107 is adjusted so that the spot S can be observed through the eyepiece lens 415. 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: Set the changeover switch 124 so that the image from the TV camera 123 of the alignment optical system 125 is displayed on the monitor TV 1)8.

On the monitor television 1) 8, a spot image conjugate to the pinhole 104a from the reference plane plate 107 is shown on the reticle plate 12.
The situation matching the intersection of the crosshairs 1 is displayed.

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

a-5: Holder 5 with adjustment mirror 50°1
The reference plane 502 of 00 is the reference lens holder 10.
The holder 500 is attached to the reference lens holder 109a with screws 503 so as to contact the reference surface 109b (see FIG. 15A) of the lens holder 9a.

a-6: Place the autocollimator 510 on the optical bench 100, and as shown in FIG.
The autocollimator 510 is directly opposed to the adjustment mirror 501 so as to coincide with the adjustment mirror 501. Thereafter, this autocollimator 510 is fixed on the optical bench 100 so that it does not move.

a-7: Remove the adjustment mirror 501 along with the holder 500 from the reference lens holder 109a.

a-8 = Known 5-axis holder (not shown) (x, yxz
The adjustment lens 520 held on the five axes of 1φ1, φ; φ1, φ indicate the horizontal and vertical inclination directions),
1 between the reference lens 109 and the autocollimator 510
Deploy. At this time, as shown in FIG. 15A, the adjustment lens 520
The center of curvature Q of the spherical surface 521 for generating the spherical wave 520a of zero coincides with the focal point F of the reference lens 109, and the plane 522 of the adjustment lens coincides with the optical axis O of the autocollimator.
It is placed perpendicular to 1.

This setting of the adjustment lens 520 makes the interference fringes between the reference light from the reference plane plate 107 projected on the monitor television 1) 8 and the object light (spherical wave) from the spherical surface 521 of the adjustment lens 520 into a one-color state. Rough positioning is performed by using the autocollimator, and then precise positioning is performed by matching the target image 51) with the reticle image 512a using the ocular observation image of the autocollimator.

(Setting of conventional hologram prototype) a-9: When the aspherical surface 523 of the adjustment lens 520 for generating the aspherical wave 523a is located at the above-mentioned setting completion position, the object from this aspherical surface 523 Light and reference plane 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 X-Y direction movement stage 21) of the hologram prototype holder 200 described above.

a-10: Switch the changeover switch 124 to display the image of the TV camera 1) of the interference fringe observation optical system on the monitor TV 1).
8 so that it is displayed.

a-1): Feed screw 208, 1) 6.217 and 218
By adjusting, for example, the first-order diffracted light of the object light (aspherical wave) from the aspherical surface 523 of the adjustment lens 520 by the adjustment hologram prototype, and the O-th-order diffracted light of the reference light from the reference plane plate 107, for example. Spatial filter 1) The interference fringes in 3 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 movement knob (not shown) and align the eyepiece lens 25 shown in FIG.
As in the observation field example No. 9, the circular indicators 260 and 261 of the reticle plates 257 and 258 are aligned.

a-13: Just to be sure, look through the autocollimator 510 and check whether the target image 51) matches the reticle index 512a, that is, whether the adjustment lens 520 is correctly positioned. Reconfirm.

If the positioning is correct, it is determined that the settings from steps (a-9) to (a-12>) have been performed correctly, and after this, the autocollimator 510
Since the adjustment lens 520 is unnecessary, it is removed.

a-14: tA water conditioning hologram prototype stage 21)
and replace it with the measurement hologram prototype 30.
0 is placed on the stage 21) and vacuum-adsorbed.

a-15: Hologram prototype holder eyepiece 259
While looking at the circular indicators 260 and 26 of the reticle 257 and 258 positioned in step <a-12).
Adjust the feed screws 216, 217° 218 so that 1 and the alignment mark 306 of the measurement hologram prototype 300 placed in step (a-14) match, and move the hologram prototype together with the stage 21). position.

(Setting the test object) a-16: Place the test object T in a known 6-axis holder (x, y, 2
, φ^, φ8, and θ (θ is rotation around the optical axis).

a-17: Switch the selector switch 124 to ARAI 1,
The image from the television camera 123 of the optical system 125 is displayed on the monitor television 1)8. The first-order diffracted spot light (
The holder that holds the test object T is adjusted so that the light (usually brighter than the 0th order diffracted light) is matched and has the smallest spot.

a-18: Next, the changeover switch 124 is switched to send the image of the television camera 1) 7 of the interference fringe observation optical system to the monitor television 1) 8. This allows monitor TV 1
) Project the interference fringes on B and finely adjust the holder so that the direction and pitch of the interference fringes are suitable for measurement.

b) Set-up 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 oblique work of the reference plane plate 107 is performed between step (a-15) and step (a-16) of the above-mentioned on-axis cent-up step.
That is, it is performed after thefting of the measurement hologram prototype is completed. This work of tilting the reference flat plate is performed in the following steps.

b-1: The off-axis adjustment microscope 410 is
As shown by the two-dot chain line in the figure, 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, eyepiece 4
15, position the microscope so that the scale line of the desired off-axis angle, for example, 2.5 degrees, is in the center of the field of view.

b-2: Tilt the reference plane plate 107 so that the reflection spot S thereby coincides with the intersection of the desired scale line (for example, a 2.5” scale line). The tilt adjustment of the reference plane plate 107 is completed. Then, remove the microscope 410.

b-3: Switch the changeover switch 124 so that the image of the television camera 123 of the alignment optical system 125 is displayed on the monitor television 1)8. Then, the micro mechanism 130 is operated to move the optical bench 130 to the turning center LD so that the reflected spot image from the reference plane plate 107 matches the intersection of the crosshairs of the reticle 121 displayed on the monitor television 1)8. Rotate around.

Great Emperor and Five Emperors (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 checking the off-axis angle, a line sensor 601 is used as shown in FIG.
Alternatively, the off-axis angle may be adjusted by directly receiving the light 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 306
The image from the objective lens 240 is directly transmitted to the area sensor 60.
2, the 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) In the example shown in FIG. 18, the hologram prototype 300
Using the hollow circular mark 606 as an alignment mark, the reticle plates 257, 2 of the alignment optical system 250
58, a black circle mark 607 having a negative-positive relationship with this circular mark 606 is arranged, and a light receiving element 608 is arranged after that.

As a result, the circular mark 606 of the hologram prototype 300 and the black circle mark 607 of the reticles 257, 258 are aligned, and the adjustment water opening 1 is adjusted so that the black circle mark 607 of the reticles 257, 258 becomes zero. Move the rear 'chiku' 257 and 258. After that, the setting of the hologram prototype for measurement is done in the same way as the light receiving element 6.
Adjust the measurement hologram prototype so that the output from 08 is zero.

(3-3) In FIG. 19A, a fine first concentric circle mark 609 is provided in place of the alignment mark 306 of the hologram prototype 300, and a second concentric circle mark having the same shape as this first concentric circle mark 609 is provided. 610, for example, on the Z-axis moving stage 205 in front of the objective lens 240.
An objective lens 240 is located very close to the directional movement stage 21).
This shows a configuration in which the device is movable in a plane perpendicular to the optical axis of the device.

The reference plate 608 having this second concentric circle mark 610 is
Moire fringes caused by both marks 609 and 610 61)
(see Figure 19B) is moved so that it disappears.

Based on the adjusted position of the reference plate 608 at this time, the first concentric mark on the measurement hologram prototype and the second concentric mark on the reference plate are
Position the hologram prototype for measurement so that moire fringes do not appear with the concentric circle mark.

(3-4) The example shown in FIG. 20 is a hologram prototype 300
In place of the alignment mark of the Fresnel lens 62
Consists of 0. That is, the light from the light source is received by the four-split detector 621, and the detector 621 is arranged 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.
The hologram prototype for measurement is set using the moved position as the reference position.

Note that if the Fresnel lens 620 has 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 hologram prototype for adjustment,
Adjustment lens 52 having a spherical surface 521 and an aspherical surface 523
Instead of using 0, as shown in FIGS. 21A and 21B, an adjustment lens 650 having only a spherical surface 521 is used.

That is, first, by executing steps (a-3) to (a-8) described above, the center of curvature Q of the spherical surface 521,
and the focal point F of the reference lens 109, and the plane 5
22 is the collimator optical axis 0. Adjustment lens 650 is set so that it is perpendicular to. Next, this adjustment lens 650 is moved backward (or advanced) by a predetermined distance MD, 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, an aspherical wave and is emitted. If a hologram prototype for adjustment is created as an interference pattern between this aspherical wave and the reference light from the reference plane plate, after moving the adjustment lens 650 as shown in FIG. 21B, the above-mentioned steps can be performed. <a-9) to step (a-1)) by using the hologram prototype for adjustment,
The hologram prototype for adjustment can be set correctly,
Furthermore, step (a-12) or step (a-1
5) allows the hologram prototype for measurement to be set correctly.

(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 301 is a phase type hologram pattern. You can also use patterns.

[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 bologram pattern in its first quadrant, FIG. 5 is a front view showing a hologram prototype holder, and FIG. 6 is a diagram showing ■-■ in FIG. 5. Fig. 7 is a cross-sectional view taken along ■-■ in Fig. 5. Fig. 8 is a perspective optical layout diagram showing the alignment optical system of the hologram prototype holder. Fig. 9 is a perspective view of the alignment optical system of the hologram prototype holder. Figures 10A to 10C are schematic diagrams showing the action of the hologram prototype holder, Figure 1) is a partial diagram showing the optical arrangement relationship between on-axis measurement and off-axis measurement, and Figure 12 shows an example of the eyepiece field of view. The figure shows an example of a pinhole reticle, Figure 13 is an optical layout diagram showing the configuration of an off-axis adjustment microscope, Figure 14 is an optical layout diagram showing the configuration of an on-axis adjustment microscope, and Figure 15A is an optical layout diagram showing the configuration of an on-axis adjustment microscope. A reference lens is used to explain the setting adjustment of the holographic interferometer of the invention.
A diagram showing the arrangement of the adjustment mirror, adjustment lens, and autocollimator, Figure 15B is a diagram showing an example of the eyepiece observation field of the autocollimator, and Figure 1.6 is a modification of the pinhole reticle. FIGS. 17 to 20 are optical layout diagrams showing examples, respectively, and FIGS.
Figures A and 21B are diagrams showing another method of setting the hologram prototype for adjustment, and Figure 22 is a diagram of the optical layout of a conventional Fizeau type interferometer. 101... Laser 104... Pinhole reticle 106...
... Collimator lens 107 ... Reference plane plate 109 ... Reference lens T ... Test object 1) 0 ... Beam splitter 1) 3 ... ... Spatial filter 1) 7.123 ... TV camera 200 ...
... Hologram prototype holder 205 ... Z-axis direction movement stage 21) ... X-Y direction movement stage 208.216.217.218 ... Feed screw 223. 232, 233...Elastic body 21
5... Spring 240... Objective lens 300... Hologram prototype 301... Hologram pattern 302...
... Distortion test pattern 306 ... Alignment mark 303 ... Black-white ratio test pattern 410 ...
... Off-axis adjustment microscope 420 ... On-axis adjustment microscope 501 ... Adjustment mirror 520.650 ... Adjustment lens 510 ...
...Autocollimator Fig. 12 □ Fig. 13 Fig. 14 Fig. 2o

Claims (4)

[Claims] (1) A collimator lens for projecting the light from the light source onto the test object as a parallel beam, and a reference lens that is placed on the exit side of the collimator lens and reflects a part of the light from the collimator lens. a reference light generating optical element for reflecting the reference light and the object light from the object, and a reference light generating optical element 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 tilted beam splitter, a hologram prototype placed on the reflection optical axis of the beam splitter, and one light wave of the object light and the reference light diffracted by the hologram prototype, and the other light wave. and an observation optical system for observing interference fringes with a holographic interferometer, wherein the reference light generating optical element is tiltable with respect to the optical axis of the collimator lens, and the observation optical system A holographic interferometer, wherein the holographic interferometer is capable of rotating at any angle about approximately the center of the exit pupil of the collimator lens. (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 includes: The holographic interferometer according to claim 1, wherein the holographic interferometer is rotatable about the center of the composite exit pupil of the reference 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 is composed of two surfaces, a front plane and a rear plane tilted at a slight angle with respect to the front plane, and one of the planes is configured to absorb light from the collimator lens. A holographic interferometer according to any one of claims 1 to 3, characterized in that part of the holographic interferometer is reflected and used as a reference light.