JP2003083726A - Measuring device and method for non-spherical surface shape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring device and a method for non-spherical surface shape capable of efficiently measuring many kinds of different shapes of inspected non- spherical surface. SOLUTION: The device is constituted of an interference optical system forming an interference fringe by overlapping measuring light reflected on an inspected non- spherical surface 10 on reference light reflected on a Fizeau surface as a reference surface, an arithmetic unit 18 calculating the shape of the inspected non-spherical surface based on the phase distribution of the interference fringe obtained with the interference optical system, and a pattern variable diffraction grating. The measuring light prior to introducing in the inspected non-spherical surface 10 is diffracted in the pattern diffraction grating 15, and its wave front shape is nearly agreed with the shape of the inspected non-spherical surface 10. Also, by using the relation between the grating pattern of the pattern variable diffraction grating 15 and the variation of wave front shape of the measuring light in front and back of the diffraction, the phase distribution of the interference fringe is corrected. Based on the phase distribution of the interference fringe obtained after the correction, the shape of inspected non-spherical surface 10 is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aspherical surface shape measuring apparatus and an aspherical surface shape measuring method for measuring an aspherical surface shape such as an aspherical lens.

[0002]

2. Description of the Related Art Conventionally, as a measurement of an aspherical shape represented by an aspherical lens, for example, a Fizeau type using a null element is known. In such a conventional device,
The coherent light emitted from the light source is split into the measurement light that passes through the reference reference surface of the Fizeau lens installed close to the aspherical surface to be inspected and the reference light reflected by this reference surface, The measurement light reflected on the spherical surface or transmitted through the aspherical surface to be tested is interfered with the reference light reflected on the standard reference surface to form an interference fringe on a predetermined observation surface. Then, the interference fringes thus obtained are analyzed to calculate the displacement amount of the measurement light with respect to the reference light, and the displacement amount is added to the shape of the reference reference surface to obtain the shape of the aspheric surface to be tested. It has become. Before the measurement light reaches the aspherical surface to be inspected, the wavefront shape is made almost the same as that of the aspherical surface to be inspected through an optical element (or an optical system) called a null element, that is, the reference reference surface is changed. Adjusted for vertical transmission.

[0003]

However, since such a null element can generate only one type of wavefront corresponding to the shape of the aspherical surface to be inspected, the null element of the aspherical surface to be inspected. When the shape changed, it was necessary to newly prepare a null element corresponding to this. Since it takes a lot of time to design and manufacture this null element, the work efficiency is very poor when several kinds of aspherical surface shapes are measured.

The present invention has been made in view of the above problems, and it is possible to easily generate a wavefront corresponding to the shape of an aspherical surface to be inspected, and to obtain various different shapes of the aspherical surface to be inspected. It is an object of the present invention to provide an aspherical surface shape measuring device and an aspherical surface shape measuring method that enable efficient measurement.

[0005]

An aspherical surface shape measuring apparatus according to a first aspect of the present invention forms an interference fringe by interfering with a reference light the measuring light reflected on the aspherical surface to be inspected or transmitted through the aspherical surface to be inspected. An aspherical surface shape measuring device configured to have an interference optical system to be operated, and a calculation means for calculating the shape of an aspherical surface to be tested based on the phase distribution of interference fringes obtained in the interference optical system, The measurement light before entering the test aspherical surface, and a pattern variable diffraction grating that diffracts at least one of the reference light before interfering with the measurement light and substantially matches its wavefront shape with the shape of the test aspherical surface, The calculation means corrects the phase distribution of the interference fringes by using the relationship between the previously stored grating pattern of the variable pattern diffraction grating and the amount of change in the wavefront shape of light before and after diffraction, and the corrected correction Based on the phase distribution of interference fringes There are determined a test aspherical surface.

Further, the aspherical surface shape measuring method according to the first aspect of the present invention determines the phase distribution of the interference fringes obtained by interfering the reference light with the measuring light reflected on the aspherical surface to be measured or transmitted through the aspherical surface to be measured. An aspherical surface shape measuring method for obtaining the shape of an aspherical surface to be tested based on a measuring light before entering the aspherical surface to be measured, and at least one of reference light before interfering with the measuring light by a variable pattern diffraction grating. The diffracted wavefront shape is made to substantially match the shape of the aspherical surface to be measured, and the interference fringes are obtained by using the relationship between the previously stored grating pattern of the variable pattern diffraction grating and the change amount of the wavefront shape of light before and after diffraction. Is corrected, and the shape of the aspherical surface to be inspected is obtained based on the corrected phase distribution of the interference fringes.

As described above, in the aspherical surface shape measuring apparatus and the aspherical surface shape measuring method according to the first aspect of the present invention, the measuring light before entering the aspherical surface to be measured and the reference light before interfering with the measuring light are measured. At least one of them is diffracted by a pattern diffraction grating to make its wavefront shape substantially match the shape of the aspherical surface to be measured, and the amount of change in the wavefront shape of the light before and after diffraction with the grating pattern of the pattern variable diffraction grating stored in advance. The phase distribution of the interference fringes is corrected by using the relationship of, and the shape of the aspherical surface to be inspected is calculated based on the corrected phase distribution of the interference fringes. It is possible to measure the shape of the aspheric surface to be tested without the need for an element. Generating a wavefront shape close to the shape of the aspheric surface to be inspected by this pattern diffraction grating is much easier than designing and manufacturing the null element according to the shape of the aspheric surface to be inspected. Even when measuring a test aspherical surface shape, the measurement can be performed efficiently. Here, when the shape of the aspheric surface to be tested is unknown,
The grating pattern of the variable pattern diffraction grating may be set so that the number of interference fringes is minimized.

Further, the aspherical surface shape measuring apparatus according to the second aspect of the present invention is an interference optical system for forming interference fringes by interfering with the reference light the measuring light reflected on the aspherical surface to be inspected or transmitted through the aspherical surface to be inspected. And an arithmetic means for calculating the shape of the aspherical surface to be inspected based on the phase distribution of the interference fringes obtained in this interference optical system. The measuring means is provided with an active mirror that reflects at least one of the measurement light before entering the measurement light and the reference light before interfering with the measurement light and substantially matches the wavefront shape thereof with the shape of the aspherical surface under test. The phase distribution of the interference fringes is corrected using the relationship between the stored active mirror shape pattern and the amount of change in the wavefront shape of the light before and after reflection, and the phase distribution of the corrected interference fringes is obtained by this. Obtain the shape of the aspheric surface to be inspected based on That.

Further, the aspherical surface shape measuring method according to the second aspect of the present invention provides the phase distribution of the interference fringes obtained by interfering with the reference light the measuring light reflected or transmitted through the aspherical surface to be inspected. An aspherical surface shape measuring method for obtaining the shape of an aspherical surface to be inspected based on an active mirror that reflects at least one of the measurement light before entering the aspherical surface to be inspected and the reference light before interfering with the measurement light. Then, the wavefront shape is made to approximately match the shape of the aspheric surface to be tested, and the phase of the interference fringes is calculated using the relationship between the shape pattern of the active mirror stored in advance and the change amount of the wavefront shape of light before and after reflection. The distribution is corrected, and the shape of the aspherical surface to be inspected is obtained based on the phase distribution of the corrected interference fringes thus obtained.

As described above, in the aspherical surface shape measuring apparatus and the aspherical surface shape measuring method according to the second aspect of the present invention, the measuring light before entering the aspherical surface to be measured and the reference light before interfering with the measuring light are measured. At least one of them is reflected by an active mirror to make its wavefront shape substantially match the shape of the aspheric surface to be tested, and the shape pattern of the active mirror stored in advance and the amount of change in the wavefront shape of light before and after reflection The phase distribution of the interference fringes is corrected using the relationship, and the shape of the aspherical surface to be inspected is obtained based on the corrected phase distribution of the interference fringes. It is possible to measure the shape of the aspherical surface to be inspected without requiring. Generating a wavefront shape close to the shape of the aspherical surface to be inspected by this active mirror is much easier than designing and manufacturing a null element according to the shape of the aspherical surface to be inspected. Even when measuring a test aspherical surface shape, the measurement can be performed efficiently. Here, when the shape of the aspherical surface to be tested is unknown, the overall shape of the active mirror may be set so that the number of interference fringes is minimized.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the configuration of an aspherical surface shape measuring apparatus according to the first aspect of the present invention, which is constructed based on a Fizeau interferometer. In this measuring apparatus, a coherent light is emitted from a light source (for example, a laser light source) 11, and its P-polarized component is transmitted through the semitransparent film 12a of the polarization beam splitter (PBS) 12 and the quarter wavelength plate 13 to the upper part of the figure. After becoming circularly polarized light, it passes through the Fizeau lens 14 in the upper part of the drawing to become measurement light. The measurement light transmitted through the Fizeau lens 14 enters the variable pattern diffraction grating 15, is reflected and diffracted to the right in the figure, and enters the aspheric surface 10 to be inspected from the left in the figure. A part of the measurement light (first-order diffracted light) incident on the aspherical surface 10 to be inspected is reflected on the surface of the aspherical surface 10 to be inspected to the left in the figure, and then returns to the variable pattern diffraction grating 15 to be reflected and diffracted downward in the figure. Fizeau lens 14 and 1 /
After passing through the four-wave plate 13 in the lower part of the figure to become S-polarized light,
The light is reflected to the left side of the figure at the semi-permeable film 12a of the polarization beam splitter 12.

A part of the light emitted from the light source 11 and transmitted through the semitransparent film 12a of the polarization beam splitter 12 and the quarter-wave plate 13 in the upper part of the drawing uses the Fizeau surface 14a of the Fizeau lens 14 as a reference reference surface. Then, the light is reflected downward in the drawing to become reference light, which is transmitted through the quarter-wave plate 13 downward in the drawing, and is then reflected leftward in the drawing by the semitransparent film 12a of the polarization beam splitter 12.

The measurement light reflected on the aspherical surface 10 to be tested and the reference light reflected on the Fizeau surface 14a, which is the reference surface, are superposed on the semi-permeable film 12a of the polarization beam splitter 12 and proceed to the left in the figure. The light is condensed by the imaging lens 16 and forms an interference fringe on the image sensor 17. The image sensor 17 includes the arithmetic unit 1
8 is connected, and the information on the phase distribution of the interference fringes formed on the image sensor 17 is sent to the arithmetic unit 18. The arithmetic unit 18 calculates the shape of the aspheric surface 10 to be inspected based on the information on the phase distribution of the interference fringes sent from the image sensor 17, and outputs a three-dimensional shape diagram of the aspheric surface 10 to be inspected or the like on a display not shown. To do. Here, the arithmetic unit 1
Data indicating the relationship between the grating pattern of the variable pattern diffraction grating 15 and the amount of change in the wavefront shape of light before and after diffraction in the variable pattern diffraction grating 15 is stored in advance in the storage section 8 of the arithmetic unit 18. The phase distribution of the interference fringes is corrected using this data, and the shape of the aspherical surface 10 to be inspected is obtained based on the corrected phase distribution of the interference fringes.

In order to measure the shape of the aspherical surface 10 to be inspected using this aspherical surface shape measuring apparatus, first, each grating element 15a (micromirror, liquid crystal, etc. of the pattern variable diffraction grating 15 is calculated by the arithmetic unit 18. FIG. The drive element of the reference) is operated to set the variable pattern diffraction grating 15 to a predetermined grating pattern. Here, whether the shape of the aspherical surface 10 to be tested is known,
Alternatively, when the shape of the aspherical surface 10 to be inspected is known to some extent and the shape can be predicted, the wavefront shape of the measurement light obtained by diffracting the variable pattern diffraction grating 15 substantially matches the known shape or the predicted shape. To set the grid pattern.

When the grating pattern of the variable pattern diffraction grating 15 is set, light is emitted from the light source 11 to form interference fringes on the image sensor 17 as described above. When the interference fringes are formed, the arithmetic unit 18 determines the wavefront shape before and after the diffraction of the measurement light from the relational data of the stored grating pattern of the variable pattern diffraction grating 15 and the change amount of the wavefront shape of the light before and after the diffraction. The amount of change is estimated, and the phase distribution of the interference fringes is corrected based on the estimated amount of change in the wavefront shape. Then, analysis is performed on the basis of the phase distribution of the corrected interference fringes thus obtained, and the shape of the aspherical surface 10 to be inspected is calculated. FIG. 2 shows an example of the grating pattern of the variable pattern diffraction grating 15.

Here, when the shape of the aspherical surface 10 to be tested is completely unknown, the variable pattern diffraction grating 1 is designed so that the number of interference fringes appearing on the image sensor 17 is minimized.
After setting the lattice pattern of No. 5, the shape of the aspherical surface 10 to be measured is measured. This is because the smaller the number of interference fringes appearing on the image sensor 17, the closer the wavefront shape of the measurement light obtained by diffracting in the variable pattern diffraction grating 15 to the shape of the aspherical surface 10 to be measured. It is because

The aspherical surface shape measurement using this measuring apparatus is performed by such a procedure, but the Fizeau lens 14 is shifted in the optical axis direction (the distance between the Fizeau surface 14a and the aspherical surface 10 to be tested is changed. It is also effective to perform a fringe scan and obtain the shape of the aspherical surface 10 to be inspected based on the change in the phase distribution of the interference fringes obtained thereby. According to such a method, the best phase data excluding the influence of noise can be obtained, so that an accurate measurement result can be obtained.

Further, each grating element of the variable pattern diffraction grating 15 operates by receiving a drive signal (specifically mainly an electric field) given to each element, and the drive signal of each grating element and the actual operation amount are If data is acquired in advance and calibration based on this data is reflected in the measurement result, a more accurate measurement result can be obtained.

Further, the variable pattern diffraction grating 15 having the same grating pattern for both the aspherical surface 10 to be measured and the reference aspherical refractor (reference aspherical surface whose shape is known). The shape of the aspherical surface 10 to be inspected may be obtained from the difference between these two measurement results. According to such a method, it is possible to obtain a precise measurement result from which an error peculiar to the measuring device is removed. If the variable pattern diffraction grating 15 is combined with a lens system having known aberrations, it can be treated like a conventional null element.

As described above, in the present aspherical surface shape measuring apparatus, the measurement light before entering the aspherical surface 10 to be measured is diffracted by the pattern diffraction grating 15 so that the wavefront shape thereof substantially matches the shape of the aspherical surface 10 to be tested. At the same time, the phase distribution of the interference fringes is corrected using the relationship between the previously stored grating pattern of the variable pattern diffraction grating 15 and the amount of change in the wavefront shape of light before and after diffraction, and the corrected after-correction phase distribution is obtained. The shape of the aspherical surface to be inspected is obtained based on the phase distribution of the interference fringes, and the shape of the aspherical surface 10 to be inspected can be measured without using the conventionally used null element. . The pattern diffraction grating 15 allows the aspherical surface 1 to be tested.
Generating a wavefront shape close to that of 0 is much easier than designing and manufacturing a null element according to the shape of the aspherical surface 10 to be measured, and measuring many kinds of aspherical surface shapes to be measured. Even if it does, the measurement can be performed efficiently.

FIG. 3 shows a modification of the aspherical surface measuring device according to the first aspect of the present invention. The aspherical surface shape measuring apparatus according to this modification is constructed based on a Twyman-Green type interference system. In this device, the light source 111
The coherent light emitted further is collimated by the beam expander 112, and then transmitted through the semitransparent film 113a of the polarization beam splitter 113 to the right in the figure (P).
It is split into a polarized light component) and a reference light (S polarized light component) reflected upward in the drawing at the semi-transparent film 113a. The measurement light transmitted through the semi-transparent film 113a of the polarization beam splitter 113 to the right in the figure is transmitted through the quarter-wave plate 114 to the right in the figure, and then is condensed by the condenser lens 115 to be aspherical surface 110 to be inspected. It will be reflected to the left of the figure. The measurement light reflected by the aspherical surface 110 to be measured is condensed by the condenser lens 115 and the quarter wavelength plate 1.
14 is transmitted to the left side of the drawing and the polarization beam splitter 113
Leading to. Semi-permeable film 113a of the polarization beam splitter 113
To the right of the figure, and then again the polarization beam splitter 1
The measurement light returning to 13 is a quarter wavelength plate 114 in the meantime.
Is S-polarized because it is transmitted twice, and therefore when the measurement light returns to the polarization beam splitter 113, it is reflected downward in the figure by the semi-transmissive film 113a.

On the other hand, the reference light reflected upward in the drawing by the semi-transmissive film 113a of the polarization beam splitter 113 is 1/4.
After passing through the wave plate 116 in the upper part of the figure, it reaches the pattern variable diffraction grating 117, where it is reflected and diffracted, and then passes through the quarter wave plate 116 in the lower part of the figure, and the polarization beam splitter 11
Up to 3. Semi-permeable film 113 of the polarization beam splitter 113
The reference light reflected in the upper part of the figure at a and returning to the polarization beam splitter 113 again has the quarter wave plate 1 in between.
Since it is transmitted twice through 16, it is P-polarized, and therefore, when the reference light returns to the polarization beam splitter 113, the semi-transmissive film 113a is transmitted downward in the figure.

The measurement light reflected by the aspherical surface 110 to be inspected and the reference light diffracted by the variable pattern diffraction grating 117 are superposed on the semi-transmissive film 113a of the polarization beam splitter 113, and proceed to the lower part of the drawing to image the imaging lens 118. Image sensor 119
Form interference fringes on top. An arithmetic unit 120 is connected to the image sensor 119, and the arithmetic unit 120 is
The shape of the aspherical surface 10 to be tested is calculated based on the phase distribution of the interference fringes formed on the image sensor 119. The detailed process of this shape calculation is the same as in the case of the device having the above-described configuration.

As in the apparatus according to the present modification, the reference light before it interferes with the measurement light is diffracted by the variable pattern diffraction grating 117 so that the wavefront shape thereof substantially matches the shape of the aspherical surface 110 to be tested. The above-mentioned aspherical surface shape measuring device (that is, a configuration in which the measurement light before entering the aspherical surface to be inspected is diffracted by the variable pattern diffraction grating so that its wavefront shape is substantially matched with the shape of the aspherical surface to be inspected). The same effect can be obtained. Although not shown in detail here, both the measurement light and the reference light are diffracted by the same or different pattern variable diffraction gratings so that the respective wavefront shapes substantially match the shapes of the aspherical surface 110 to be tested. May be. Further, this modification has a configuration based on the Twyman-Green type interference system, but this can be replaced with a configuration based on the Fizeau side interference system.

FIG. 4 shows an example of the construction of an aspherical measuring device according to the second aspect of the present invention, which is constructed on the basis of a Fizeau type interference system. In this measuring device, a coherent light is emitted from a light source (for example, a laser light source) 211, and its P-polarized component is the semitransparent film 2 of the polarization beam splitter 212.
After passing through the 12a and the quarter-wave plate 213 upward in the drawing to become circularly polarized light, the light is passed through the Fizeau lens 214 upward in the drawing to become measurement light. The measurement light transmitted through the Fizeau lens 214 enters the active mirror 215, is reflected to the right in the figure, and is incident on the aspherical surface 210 to be inspected from the left in the figure. The measurement light incident on the aspherical surface 210 to be inspected is reflected to the left side of the drawing on the surface of the aspherical surface 210 to be inspected, then returns to the active mirror 215 and is reflected downward in the figure, and the Fizeau lenses 214 and 1
After passing through the / 4 wavelength plate 213 downward in the drawing to become S-polarized light, it is reflected to the left in the drawing at the semi-transmissive film 212a of the polarization beam splitter 212.

A part of the light emitted from the light source 211 and transmitted through the semi-transmissive film 212a of the polarization beam splitter 212 and the quarter wavelength plate 213 in the upper part of the drawing uses the Fizeau surface 214a of the Fizeau lens 214 as a reference reference surface. Then, the light is reflected downward in the drawing to become reference light, which is transmitted through the quarter-wave plate 213 downward in the drawing and then reflected leftward in the drawing by the semi-transmissive film 212a of the polarization beam splitter 212.

The measurement light reflected on the aspherical surface 210 to be measured and the reference light reflected on the Fizeau surface 214a which is the reference surface are the semi-transparent film 21 of the polarization beam splitter 212.
In the state where they are superposed on each other at 2a, they proceed to the left in the drawing, and are condensed by the imaging lens 216 to form interference fringes on the image sensor 217. Image sensor 217
An arithmetic unit 218 is connected to the arithmetic unit 218, and information on the phase distribution of the interference fringes formed on the image sensor 217 is sent to the arithmetic unit 218. The arithmetic unit 218 calculates the shape of the aspherical surface 210 to be inspected based on the information on the phase distribution of the interference fringes sent from the image sensor 217, and outputs a three-dimensional shape diagram or the like of the aspherical surface 210 to be inspected on a display not shown. To do. Here, the shape pattern of the active mirror 215 and the active mirror 215 are stored in the storage unit of the arithmetic unit 218.
The data indicating the relationship with the amount of change in the wavefront shape of light before and after the reflection is stored in advance.
Reference numeral 8 corrects the phase distribution of the interference fringes using this data, and obtains the shape of the aspherical surface 210 to be inspected based on the corrected phase distribution of the interference fringes.

In order to measure the shape of the aspherical surface 210 to be tested using this aspherical surface shape measuring apparatus, first, the driving element of each mirror element of the active mirror 215 is operated by the arithmetic unit 218 to activate the active mirror 215. Is set to a predetermined shape pattern. Here, if the shape of the aspherical surface 210 to be tested is known, or if the shape of the aspherical surface 210 to be tested is known to some extent and the shape can be predicted, the active mirror 2
The shape pattern is set so that the wavefront shape of the measurement light obtained by reflection at 15 substantially matches the known shape or predicted shape.

When the shape pattern of the active mirror 215 is set, light is emitted from the light source 211 to form interference fringes on the image sensor 217 as described above. When the interference fringes are formed, the arithmetic unit 218 determines from the relationship data between the stored shape pattern of the active mirror 215 and the amount of change in the wavefront shape of light before and after reflection, the change in the wavefront shape before and after reflection of the measurement light. The amount is estimated, and the phase distribution of the interference fringes is corrected based on the estimated amount of change in the wavefront shape. Then, analysis is performed based on the phase distribution of the corrected interference fringes obtained in this way, and the aspherical surface 2 to be measured to be obtained is obtained.
10 shapes are calculated.

Here, when the shape of the aspherical surface 210 to be tested is completely unknown, the active mirror 215 is arranged so that the number of interference fringes appearing on the image sensor 217 is minimized.
After the shape pattern is set, the shape of the aspherical surface 210 to be measured is measured. This is the image sensor 217
This is because the wavefront shape of the measurement light obtained by being reflected by the active mirror 215 becomes closer to the shape of the aspherical surface 210 to be measured, as the number of interference fringes appearing above is smaller.

The aspherical surface shape measurement using this measuring apparatus is performed by such a procedure, but the Fizeau lens 214 is shifted in the optical axis direction (the Fizeau surface 214a and the aspherical surface 2 to be inspected 2).
It is also effective to perform a fringe scan (changing the distance from 10) and obtain the shape of the aspherical surface 210 to be inspected based on the change in the phase distribution of the interference fringes obtained thereby. According to such a method, the best phase data excluding the influence of noise can be obtained, so that an accurate measurement result can be obtained.

Further, each mirror element of the active mirror 215 operates by receiving a drive signal (specifically, mainly an electric field) given to each of them, but the data of the drive signal of each mirror element and the actual operation amount are given. Is acquired in advance and the calibration based on this data is reflected in the measurement result, a more accurate measurement result can be obtained.

Further, both the measurement target aspherical surface 210 and the reference aspherical surface reflex standard are subjected to shape measurement using the active mirror 215 set to the same shape pattern, and both measurement results are obtained. From the difference of
The shape of 0 may be obtained. According to such a method, it is possible to obtain a precise measurement result from which an error peculiar to the measuring device is removed. In addition, the active mirror 215
Can be handled like a conventional null element by combining with a lens system with known aberration.

As described above, in the present aspherical surface shape measuring apparatus, the measurement light before entering the aspherical surface 210 to be measured is reflected by the active mirror 215 so that its wavefront shape is substantially the same as the shape of the aspherical surface 210 to be tested. In addition, the phase distribution of the interference fringes is corrected by using the relationship between the shape pattern of the active mirror 215 stored in advance and the amount of change in the wavefront shape of light before and after reflection, and the correction thus obtained is obtained. The shape of the aspherical surface 210 to be inspected is obtained based on the phase distribution of the interference fringes later, and the shape of the aspherical surface 210 to be inspected can be measured without using the conventionally used null element. It is possible. In order to generate a wavefront shape close to the shape of the aspherical surface 210 to be tested by this active mirror 215, the null element is designed according to the shape of the aspherical surface 210 to be tested.
It is much easier than manufacturing, and the measurement can be efficiently performed even when measuring many kinds of aspherical shapes to be tested.

FIG. 5 shows a first modification of the aspherical surface shape measuring apparatus according to the second invention. The aspherical surface shape measuring apparatus according to this modification is constructed based on a Twyman-Green type interference system. In this device, the light source 3
The coherent light beam emitted from the beam splitter 11 is collimated by the beam expander 312, and then the polarized beam splitter 31
In FIG. 3, the semi-transparent film 313a is split into measurement light (P-polarized light component) that is transmitted to the right in the figure and reference light (S-polarized light component) that is reflected upward in the semi-permeable film 313a. The measurement light transmitted through the semitransparent film 313a of the polarization beam splitter 313 to the right in the figure is transmitted through the quarter-wave plate 314 to the right in the figure, and then is condensed by the condenser lens 315, and then is aspherical surface 20 to be inspected. It will be reflected to the left of the figure. The measurement light reflected by the aspherical surface 310 to be measured passes through the condenser lens 315 and the quarter-wave plate 314 to the left in the drawing and reaches the polarization beam splitter 313. Semi-permeable film 3 of polarization beam splitter 313
13a is transmitted to the right side of the drawing and then returned to the polarization beam splitter 313 again, it is S-polarized because it is transmitted through the quarter wavelength plate 314 twice during that time, and therefore the measurement light is When it returns to the polarization beam splitter 313, it is reflected by the semi-permeable film 313a downward in the figure.

On the other hand, the reference light reflected upward in the figure at the semi-transparent film 313a of the polarization beam splitter 313 is 1/4.
After passing through the wave plate 316 in the upper part of the figure, the active mirror 31
7, and after being reflected here, the light passes through the quarter-wave plate 316 downward in the figure and reaches the polarization beam splitter 313. The reference light reflected upward in the drawing by the semitransparent film 313a of the polarization beam splitter 313 and returning to the polarization beam splitter 313 again passes through the quarter-wave plate 316 twice during that time, and is therefore P-polarized. Therefore, when the reference light returns to the polarization beam splitter 313, it passes through the semipermeable membrane 313a downward in the figure.

The measurement light reflected by the aspherical surface 310 to be measured and the reference light reflected by the active mirror 317 are superposed on the semi-transparent film 313a of the polarization beam splitter 313, and proceed to the lower part of the drawing. The light is condensed to form interference fringes on the image sensor 319. The image sensor 319 has an arithmetic unit 32.
0 is connected, and the arithmetic unit 320 calculates the shape of the aspherical surface 310 to be tested based on the phase distribution of the interference fringes formed on the image sensor 319. The detailed process of this shape calculation is the same as in the case of the device having the above-described configuration.

Even in the configuration of the apparatus according to the present modification, the reference light before it interferes with the measurement light is reflected by the active mirror 25 so that its wavefront shape is substantially the same as the shape of the aspherical surface 310 to be tested. Aspherical surface shape measuring device (that is, the measurement light before entering the aspherical surface to be measured is reflected by an active mirror so that its wavefront shape is almost matched with the shape of the aspherical surface to be measured) The effect can be obtained. Although not shown in detail here, both the measurement light and the reference light are reflected by the same or different active mirrors so that the wavefront shapes of the respective measurement light beams and the reference light beams are substantially matched with the shape of the aspherical surface 310 to be measured. Good. Further, this modification has a configuration based on the Twyman-Green type interference system, but it can be replaced with a configuration based on the Fizeau side interference system.

FIG. 6 shows a second modification of the aspherical surface shape measuring apparatus according to the second aspect of the present invention, which is constructed on the basis of a Fizeau type interference system. In this device, the P-polarized component of the coherent light emitted from the light source (for example, laser light source) 411 is the semi-transparent film 41 of the polarization beam splitter 412.
After passing through the 2a and 1/4 wave plate 413 upward in the figure to become circularly polarized light, it reaches the active mirror 414 and is reflected to the right in the figure. The light reflected by the active mirror 414 passes through the Fizeau lens 415 to the right in the figure to become measurement light, which is incident on the aspherical surface 410 to be tested. Aspheric surface to be tested 410
The measurement light incident on is reflected to the left in the figure on the surface of the aspherical surface 410 to be tested, then passes through the Fizeau lens 415 to the left in the figure and returns to the active mirror 414. Active mirror 4
The measurement light returned to 14 is reflected downward in the figure, transmitted through the quarter-wave plate 413 downward in the figure to be S-polarized, and reflected to the left side in the figure at the semitransparent film 412a of the polarization beam splitter 412. . Here, the shape of the Fizeau surface 415a, which is the final surface of the Fizeau lens 415, is an aspherical shape similar to the aspherical surface 410 to be tested with the paraxial curvature center of the aspherical surface 410 to be the reference. The Fizeau surface 415a is installed at a position very close to the aspherical surface 410 to be tested.

Also, one of the light emitted from the light source 411, transmitted through the semitransparent film 412a of the polarization beam splitter 412 and the quarter wavelength plate 413 in the upper part of the figure, and reflected by the active mirror 414 to the right side of the figure. Fizeau lens 415
Of the Fizeau surface 415a, which is the final surface of the mirror, is reflected to the left in the drawing to become reference light, and the active mirror 414
Return to. The reference light returning to the active mirror 414 is reflected downward in the figure, passes through the quarter wavelength plate 413 downward in the figure, and then enters the polarization beam splitter 412, and the semitransparent film 41 thereof is formed.
At 2a, it reflects to the left in the figure.

The measurement light reflected on the aspherical surface 410 to be measured and the reference light reflected on the Fizeau surface 415a which is the reference surface are the semi-transparent film 41 of the polarization beam splitter 412.
Proceed to the left in the figure in the state of overlapping in 2a,
It is condensed by the imaging lens 416 to form an interference fringe on the image sensor 417. Image sensor 41
An arithmetic unit 418 is connected to 7 and the arithmetic unit 418 calculates the shape of the aspherical surface 410 to be inspected based on the phase distribution of the interference fringes formed on the image sensor 417.

In order to measure the shape of the aspherical surface 410 to be tested using this aspherical surface shape measuring apparatus, first, the active mirror 41 is used.
Part of the light reflected at 4 (measurement light) is the Fizeau surface 4
15a is transmitted vertically. For this, the driving device of each mirror element of the active mirror 414 is operated by the arithmetic unit 418 so that the wavefront shape of the light reflected by the active mirror 414 matches the shape of the Fizeau surface 415a. The pattern is set, and at the same time, the distance between the lenses forming the Fizeau lens 415 is adjusted.

In order for the wavefront shape of the light reflected by the active mirror 414 to match the shape of the Fizeau surface 415a, the light is first blocked between the Fizeau surface 415a and the aspherical surface 410 to be tested. A light blocking member is inserted so that light does not strike the aspherical surface 410 to be tested (the aspherical surface 410 to be tested may be removed from the measurement device). Then, the polarization state of the light emitted from the light source 411 is adjusted so that part of the light (S-polarized component) is polarized by the polarization beam splitter 4.
Twelve semi-permeable membranes 412a are reflected to the right in the figure. Semi-permeable film 412a of the polarization beam splitter 412
The light reflected at is transmitted through the quarter-wave plate 419 to the right in the figure, and then reaches the reference mirror 420, where it is reflected to the left in the figure, and then is transmitted through the quarter-wave plate 419 and the polarization beam splitter 412. The membrane 412a penetrates to the left in the figure.

The other part of the light emitted from the light source 411 (P-polarized component) passes through the semitransparent film 412a of the polarization beam splitter 412 and the quarter wavelength plate 413 upward in the figure. This light is reflected by the active mirror 414 to the right in the figure and reaches the Fizeau surface 415a of the Fizeau lens 415, where it is reflected to the left in the figure and then the active mirror 415.
At the bottom of FIG. And a quarter wave plate 41
3 is transmitted to the lower side of the figure and is reflected to the left side of the figure at the semi-permeable film 412a of the polarization beam splitter 412. Both of these lights are superposed on each other, and the polarization beam splitter 4
The analyzer 421 inserted and installed on the left side of 12 is transmitted to the left side of the drawing and is condensed by the imaging lens 416 to form an interference fringe on the image sensor 417.

When interference fringes are formed on the image sensor 417, the shape pattern of the active mirror 414 is adjusted so that the number of interference fringes is minimized. As a result, the wavefront shape of the light obtained through the active mirror 414 is in a state substantially matching the shape of the Fizeau surface 415a, and is transmitted vertically through the Fizeau surface 415a.

When such preparations are completed, the actual measurement is started. When the shape pattern of the active mirror 414 is set as described above, light is emitted from the light source 411 to form interference fringes on the image sensor 417. In this main measurement, the light blocking member inserted between the Fizeau surface 415a and the aspherical surface 410 to be inspected is removed (or the aspherical surface to be inspected 410 is placed on the apparatus) and the aspherical surface 30 to be inspected is removed. A light blocking member that blocks light is inserted between the quarter wavelength plate 419 and the reference mirror 420 while the light is shined on (or the quarter wavelength plate 419 and the reference mirror 420 are removed). Further, it is preferable to remove the aforementioned analyzer 421 inserted and installed on the left side of the polarization beam splitter 412 (this increases the light amount).

When the interference fringes are formed on the image sensor 417, the arithmetic unit 418 determines the shape of the aspherical surface 410 to be tested based on the information obtained from the interference fringes. Here, the interference fringes are obtained as information indicating the difference between the reference reference surface, that is, the Fizeau surface 415a and the aspherical surface 410 to be inspected. Therefore, information on this difference is obtained and the known Fizeau surface 415 is obtained.
The target shape of the aspherical surface 410 to be tested can be obtained by adding it to the shape data of a.

The measurement of the aspherical surface shape using the aspherical surface shape measuring apparatus according to the second modification is performed by such a procedure, but the Fizeau lens 415 is shifted in the optical axis direction (the Fizeau surface 415a and the inspection target). It is also effective to perform a fringe scan (changing the distance from the aspherical surface 410) and obtain the shape of the aspherical surface 410 to be tested based on the change in the phase distribution of the interference fringes. According to such a method, the best phase data in which the influence of noise is removed can be obtained, so that the shape can be accurately measured. When measuring different aspherical shapes using this measuring device, the Fizeau surface 4
The final lens of the Fizeau lens 415 having 15a is replaced with a lens having a Fizeau surface having substantially the same shape as the shape of the aspherical surface 410 to be tested.

The second modification of the aspherical surface shape measuring apparatus according to the second aspect of the present invention has been described above, but the same configuration is applied to the aspherical surface shape measuring apparatus according to the first aspect of the present invention. be able to. In this case, the active mirror in the above modification may be replaced with a variable pattern diffraction grating so that part of the light (measurement light) diffracted by the variable pattern diffraction grating passes vertically through the Fizeau surface 415a.

Although the preferred embodiments of the present invention have been described above, the scope of the present invention is not limited to those shown in the above embodiments. For example, all the polarization beam splitters used in the above-described embodiments can be replaced with half mirrors. Further, the aspherical surface shape measuring apparatus (and the aspherical surface shape measuring method) according to the present invention shown in the above embodiments are all applied to the Fizeau interferometer using the Fizeau lens or the Twyman-Green interferometer. However, these are merely examples, and the present invention can be applied to interferometers having other configurations, such as Michelson type interferometers and Maha-Zehnder type interferometers.

[0051]

As described above, in the aspherical surface shape measuring apparatus and method according to the first aspect of the present invention, the measuring light before entering the aspherical surface to be inspected and the reference before interfering with the measuring light. At least one of the light is diffracted by the pattern diffraction grating to make its wavefront shape substantially match the shape of the aspheric surface to be measured, and the pre-stored grating pattern of the variable pattern diffraction grating and the change in the wavefront shape of the light before and after the diffraction. The phase distribution of the interference fringes is corrected using the relationship with the amount, and the shape of the aspherical surface to be inspected is obtained based on the corrected phase distribution of the interference fringes, which is conventionally used. It is possible to measure the shape of the aspheric surface to be tested without requiring a null element. Generating a wavefront shape close to the shape of the aspheric surface to be inspected by this pattern diffraction grating is much easier than designing and manufacturing the null element according to the shape of the aspheric surface to be inspected. Even when measuring a test aspherical surface shape, the measurement can be performed efficiently. Here, when the shape of the aspheric surface to be tested is unknown,
The grating pattern of the variable pattern diffraction grating may be set so that the number of interference fringes is minimized.

Further, in the aspherical surface shape measuring apparatus and method according to the second aspect of the present invention, at least one of the measuring light before entering the aspherical surface to be inspected and the reference light before interfering with the measuring light is activated. By using a relationship between the shape pattern of the active mirror stored in advance and the amount of change in the wavefront shape of the light before and after reflection, while reflecting the wavefront shape by the mirror The phase distribution of the interference fringes is corrected, and the shape of the aspherical surface under test is obtained based on the corrected phase distribution of the interference fringes, which requires the conventionally used null element. It is possible to measure the shape of the aspheric surface to be inspected without the need. Generating a wavefront shape close to the shape of the aspherical surface to be inspected by this active mirror is much easier than designing and manufacturing a null element according to the shape of the aspherical surface to be inspected. Even when measuring a test aspherical surface shape, the measurement can be performed efficiently. Here, when the shape of the aspherical surface to be tested is unknown, the overall shape of the active mirror may be set so that the number of interference fringes is minimized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of an aspherical surface shape measuring apparatus according to a first aspect of the present invention.

FIG. 2 is a diagram showing an example of a pattern in a variable pattern diffraction grating.

FIG. 3 is a diagram showing a modification of the aspherical surface shape measuring apparatus according to the first aspect of the present invention.

FIG. 4 is a diagram showing a configuration example of an aspherical surface shape measuring device according to a second aspect of the present invention.

FIG. 5 is a diagram showing a first modification of the aspherical surface shape measuring apparatus according to the second invention.

FIG. 6 is a diagram showing a second modification of the aspherical surface shape measuring apparatus according to the second invention.

[Explanation of symbols]

10 Inspected aspherical surface 11 light source 12 Polarizing beam splitter 12a semipermeable membrane 13 1/4 wave plate 14 Fizeau lens 14a Fizeau surface 15 variable pattern diffraction grating 16 Imaging lens 17 Image sensor 18 arithmetic unit

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2F064 AA09 BB04 EE02 EE05 FF01                       GG14 GG23 GG44 HH03 JJ01                 2F065 AA54 BB05 BB22 CC22 DD03                       DD06 FF51 GG04 JJ03 JJ26                       LL10 LL12 LL19 LL36 LL37                       LL42 QQ28                 2G086 FF01

Claims (6)

[Claims] 1. An interference optical system for forming interference fringes by causing measurement light reflected by an aspherical surface to be inspected or transmitted through the aspherical surface to be inspected to interfere with reference light, and the interference fringes obtained in the interference optical system. An aspherical surface shape measuring device configured to include a calculation unit that calculates the shape of the aspherical surface to be inspected based on the phase distribution of the measurement light and the measurement light before entering the aspherical surface to be inspected. A pattern variable diffraction grating that diffracts at least one of the reference light before interfering with the measurement light and substantially matches the wavefront shape thereof with the shape of the aspherical surface to be inspected is provided, and the arithmetic means is the previously stored pattern. The phase distribution of the interference fringes is corrected using the relationship between the grating pattern of the variable diffraction grating and the amount of change in the wavefront shape of light before and after the diffraction, and based on the phase distribution of the corrected interference fringes thus obtained. Before Aspheric surface measuring apparatus and obtaining a test aspherical surface. 2. An aspherical surface for obtaining the shape of the aspherical surface to be inspected, based on a phase distribution of interference fringes obtained by interfering the measurement light reflected on the aspherical surface to be inspected or transmitted through the aspherical surface to be inspected with reference light. A shape measuring method, wherein at least one of the measuring light before entering the aspherical surface to be tested and the reference light before interfering with the measuring light is diffracted by a pattern variable diffraction grating to obtain the wavefront shape thereof. The phase distribution of the interference fringes is corrected using the relationship between the previously stored grating pattern of the variable pattern diffraction grating and the amount of change in the wavefront shape of light before and after the diffraction, while substantially matching the shape of the inspection aspherical surface. Then, the aspherical surface shape measuring method is characterized in that the shape of the aspherical surface under test is obtained based on the phase distribution of the corrected interference fringes thus obtained. 3. The aspherical surface shape measuring method according to claim 2, wherein the grating pattern of the variable pattern diffraction grating is set so that the number of the interference fringes is minimized. 4. An interference optical system that forms interference fringes by interfering measurement light reflected by the aspherical surface to be measured or transmitted through the aspherical surface to be tested with reference light, and the interference fringes obtained in the interference optical system. An aspherical surface shape measuring device configured to include a calculation unit that calculates the shape of the aspherical surface to be inspected based on the phase distribution of the measurement light and the measurement light before entering the aspherical surface to be inspected. An active-type mirror that reflects at least one of the reference light before it interferes with the measurement light and substantially matches the wavefront shape thereof with the shape of the aspherical surface under test is provided, and the arithmetic means is the previously stored active-type mirror. Correct the phase distribution of the interference fringes using the relationship between the shape pattern of the mirror and the amount of change in the wavefront shape of the light before and after the reflection,
An aspherical surface shape measuring device, characterized in that the shape of the aspherical surface under test is obtained based on the phase distribution of the corrected interference fringes thus obtained. 5. An aspherical surface for obtaining the shape of the aspherical surface to be inspected, based on a phase distribution of interference fringes obtained by interfering the measuring light reflected on the aspherical surface to be inspected or transmitted through the aspherical surface to be inspected with reference light. A shape measuring method, wherein at least one of the measuring light before entering the aspherical surface to be measured and the reference light before interfering with the measuring light is reflected by an active mirror to measure the wavefront shape thereof. While substantially matching the shape of the aspherical surface, the phase distribution of the interference fringes is corrected using the relationship between the shape pattern of the active mirror stored in advance and the amount of change in the wavefront shape of light before and after the reflection, An aspherical surface shape measuring method characterized in that the shape of the aspherical surface under test is obtained based on the phase distribution of the corrected interference fringes obtained in this way. 6. The aspherical surface shape measuring method according to claim 5, wherein the shape pattern of the active mirror is set so as to minimize the number of the interference fringes.