JPH10221030A - Aspherical shape measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable application to an aspherical shape in a wide range by calculating the measured surface shape on the basis of the data of measured surface shape obtained from an interference fringe and a detected displacement amount. SOLUTION: First, the inspected surface 13a of an inspected lens 13 is aligned with the measuring null wave front of measuring light emitted from a null element 2 to be covered all with fringes. Next, the inspected lens 13 is disposed such that the inspected surface 13a forms the apex reflection relative to the spheric reference wave front 11 emitted from the null element 2. A distance L1 between two measuring conditions thus obtained in the optical axis direction is measured. Thus, on the basis of measured surface shape data obtained from an interference fringe when a measured object is provided in a predetermined measuring position and the positional displacement amount between a predetermined measuring position and an alignment position detected by a displacement amount detecting means, the measured surface shape is calculated, so that application to the measurement of the aspheric surface shape is enabled in a wide range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aspherical shape measuring apparatus for measuring an aspherical shape of an aspherical lens using a null measurement wavefront generated by a null element.

[0002]

2. Description of the Related Art As a method for measuring the surface shape of an aspherical lens having an aspherical surface with high accuracy, a two-wavefront M is used.
A method using a ZP (master zone plate) is disclosed in JP-A-6-11323.

In this method, a single ZP (zone plate) element generates a shape measurement pattern for generating an aspherical wave for measuring the shape of a lens and a spherical wave for alignment of a test surface. By providing an alignment pattern and converging a spherical wave near the vertex of the test lens at a predetermined measurement position for measuring the surface shape, the shape of the test surface is measured, and the measurement optical axis direction of the test surface is measured. Is characterized in that the positioning of the lens can be performed without moving the test lens as much as possible.

[0004]

However, if an alignment pattern is present in the effective area of the shape measurement pattern, a wavefront for alignment becomes noise during shape measurement, so a shield must be inserted in the optical path. And an unmeasurable area occurs. Further, in order to avoid this, ZP outside the effective area of the shape measurement pattern, that is, ZP
Even when an alignment pattern is provided on the outer periphery of the element, depending on the shape of the aspherical surface, the line width of the alignment pattern is required to focus the spherical wave near the vertex of the test lens at the planned measurement position. There is a problem that the value becomes unrealistic.

An object of the present invention is to provide an aspherical shape measuring apparatus applicable to a wide range of aspherical shapes.

[0006]

FIG. 1 shows an embodiment of the present invention.
3, the invention according to claim 1 is applied to an aspherical shape measuring device that measures an aspherical shape of a surface 13a to be measured formed on the object 13 to be measured. Then, the interferometer main body 102 that forms interference fringes based on the mutual interference between the reference light and the measurement light, and the wavefront of the light emitted from the interferometer main body 102 is converted into the aspherical wave 10 having substantially the same shape as the surface 13a to be measured. Element 2 for performing the measurement and the interferometer body 1
The conversion element 2 for converting the wavefront of the light emitted from the element 02 into a spherical wave 11 converged toward the focal point O, and the aspherical wave 10 having a shape substantially equal to the surface 13a to be measured via the null element 2 are measured. The planned measurement position to be irradiated on the surface 13a and the conversion element 2
The measured surface 13a at the focal point O of the spherical wave 11 formed by
Holding means 3 for movably holding the DUT 13 with an alignment position at which the vertices of the object coincide with each other; displacement amount detecting means 7 for detecting a positional displacement amount between the planned focal position and the alignment position; 3, when the object 13 is set at the planned measurement position, the reference light and the surface
Surface shape data obtained from interference fringes due to mutual interference of measurement light obtained by reflection at 3a;
The above object is achieved by providing the calculating means 200 for calculating the shape of the surface 13a to be measured based on the displacement amount detected by the above.

In the section of the means for solving the above-mentioned problems, which explains the configuration of the present invention, the drawings of the embodiments of the present invention are used to make the present invention easy to understand. However, the present invention is not limited to this.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of an aspherical shape measuring apparatus according to the present invention will be described with reference to FIG. First, the test surface 13a of the test lens 13 is aligned with the measurement null wavefront 10 of the measurement light emitted from the null element 2 so as to be a single stripe. Assuming that the aspherical shape of the test surface 13a is W1 and the measured null wavefront shape uniquely determined according to the aspherical shape is N1, the obtained measurement data ΔW1 is “ΔW
1≡W1-N1 ”.

On the other hand, if the design null wavefront shape is N0,
The deviation shape ΔN1 of N1 with respect to N0 is “ΔN1≡N1
−N0 ”. Therefore, the deviation shape ΔW0 of W1 with respect to N0 is represented by “ΔW0≡W1-N0 = ΔW1 + Δ
N1 ".

Next, the test lens 13 is arranged so that the test surface 13a forms a vertex reflection with respect to the spherical reference wavefront 11 emitted from the null element 2.

The distance L1 in the optical axis direction between the two measurement states obtained above is measured. On the other hand, if the spatial relative positional relationship between the measured null wavefront 10 and the reference wavefront 11 is considered on the basis of the design value, the distance L0 that gives the measured null wavefront 10 represented by the design value can be obtained from the calculation. The subtraction distance L1-L0 between the two is obtained.
Gives the above-mentioned deviation shape of ΔN1, and when its function is represented by f (ΔL), “ΔN1 = f (L1−L
0) ".

From the above relationship, the deviation shape ΔW0 of the test surface 13a with respect to the designed null wavefront is

ΔW0 = ΔW1 + f (L1−L0) Equation (1) is obtained.

First Embodiment Hereinafter, a first embodiment of an aspherical shape measuring apparatus according to the present invention will be described with reference to FIGS.

As shown in FIG. 2, the aspherical shape measuring apparatus according to the present embodiment includes an interferometer 100, an arithmetic unit 200, and a monitor 300 for alignment. Interferometer 100
Comprises an optical system device 101, an interferometer main body 102, and an interference fringe imaging device (CCD camera) 103 for imaging an interference fringe formed in the interferometer main body 102. The device 200 and the monitor 300 are connected respectively.

As shown in FIG. 3, an optical system apparatus 101 includes a Fizeau flat 1 on which a plane wave emitted from an interferometer body 102 is incident, and a ZP for converting a light beam transmitted through the Fizeau flat 1 into a null wavefront and a spherical wave. (Zone plate) The interferometer 10 while holding the element 2 and the lens 13 to be inspected
And a holding mechanism 3 for moving in the direction of the zero measurement optical axis.

In FIG. 3, reference numeral 2a denotes a concentric diffraction grating pattern for a null wavefront formed on the upper surface of the ZP (zone plate) element 2, and 2b denotes a ZP (zone plate) surrounding the null wavefront diffraction grating pattern 2a. 7 shows a similarly concentric alignment diffraction grating pattern formed on the outer peripheral portion of the upper surface of the element 2. As shown in FIGS. 1 and 3, a measurement null wavefront 10 for interference measurement is formed by a null wavefront diffraction grating pattern 2 a at a predetermined position to have an aspherical shape substantially equivalent to the design shape of the test surface 13 a. Is done.
The alignment diffraction grating pattern 2b forms a spherical wave 11 for positioning the lens 13 to be measured.

The holding mechanism 3 includes a holding portion 3a for holding the lens 13 to be measured, a sliding portion 3b which abuts on the holding portion 3a to support the holding portion 3a, and a measuring light of the interferometer 100 for the sliding portion 3b. And a rail portion 3c slidably supported along the axis X. By sliding the sliding portion 3b along the rail portion 3c, the test lens 13 held by the holding portion 3a can be translated in the measurement optical axis direction of the interferometer 100.

In FIG. 3, reference numeral 7 denotes a detecting device for detecting the displacement of the holder 3a in the direction of the measuring optical axis. In FIG. 3, a laser length measuring device that is usually used for high-accuracy measurement is exemplified as the detecting device 7. The detection device (laser length measuring device) 7 generates a frequency-stabilized laser beam for length measurement, distributes the light beam to a reference beam and a measurement beam by a beam splitter, and detects an interferometer signal of two beams. It has a main body 7a and a mirror 7b attached to the holding section 3a for reflecting the measurement light.

In order to reduce Abbe error, the optical axis of the measuring beam of the detector 7 coincides with the measuring optical axis X of the interferometer 100. When measuring the eccentricity by using the interference measurement light from the back surface (the upper surface in FIG. 3) of the test lens 13, the measurement light axis X of the interferometer 100 is used as the symmetry axis for the two positions. The measurement may be performed.

As shown in FIG. 3 and FIG. 1, a plane wave emitted from the interferometer main body 102 is vertically incident on a high-precision reference surface 1a formed on the Fizeau flat 1, and forms one side for forming interference fringes. A measurement wavefront (reflected light) is generated. The measurement light flux transmitted through the high-precision reference surface 1a is ZP
(Zone plate) A measurement null wavefront 10, which is incident on the element 2 and has an aspherical shape substantially equivalent to the design shape at a predetermined position.
Further, a spherical wave 11 condensed at the focal point O in FIG. 1 is generated. The Fizeau flat 1 may be omitted by providing the ZP element 2 with a high-precision reference surface.

The test lens 13 set at a predetermined position (scheduled measurement position) for interference measurement by the holding mechanism 3
The reflected light from the light source becomes the other measurement wavefront, and returns to the interferometer main body 102 together with the one measurement wavefront reflected on the high-precision reference surface 1a of the Fizeau flat 1. The two measurement wavefronts interfere with each other in the interferometer main body 102, and the formed interference fringes are imaged by the interference fringe imaging device 103, and the imaging signals are output to the arithmetic device 200 and the monitor 300.

The arithmetic unit 200 includes an interference fringe imaging device 103
, And performs calculations for shape measurement. The arithmetic device 200 converts image information from the interference fringe imaging device 103 in the interferometer main body 102 into optical path difference data, and calculates a shape error of the surface 13a to be inspected.

The monitor 300 displays an image of the interference fringe itself, and the image on the monitor 300 is used when adjusting the position of the lens 13 to be inspected. That is, when the position of the test lens 13 is adjusted to make the fringe one-color state as much as possible, the holding mechanism 3 is operated while viewing the image on the monitor 300.

An example of a procedure for measuring the shape of the surface 13a of the lens 13 to be measured using the aspherical shape measuring apparatus of the first embodiment configured as described above will be described.
Next, a description will be given.

First, the test lens 13 is attached to the holding mechanism 3, and the test lens 13 is set at a predetermined measurement position by adjusting the holding mechanism 3. Specifically, the measurement null wavefront 1
While holding the monitor 300, the holding mechanism 3 is set so that 0 is incident on the surface 13a perpendicularly as much as possible (one color of the stripe).
Is operated to adjust the position of the test lens 13 in the optical axis X direction.

The null wavefront 10 obtained via the null wavefront diffraction grating pattern 2a is reflected by the test surface 13a of the test lens 13 whose position has been adjusted, and this reflected light beam forms interference fringes. Is the measured wavefront. Interferometer body 10
2 is converted into measurement data ΔW1 by processing in the arithmetic device 200,
Stored in 0. Further, the position of the test lens 13 in the direction of the optical axis X is measured by the detection device 7 and stored similarly.

Next, an operation for specifying the position of the test lens 13 in the above-described interference measurement is performed. As described above, the alignment pattern 2b provided on the outer peripheral portion of the upper surface of the ZP (zone plate) element 2 generates a convergent spherical wave by diffraction. The light condensing position (the position of the focal point O) is determined by the ease of manufacturing the ZP (zone plate) element 2 and the trade-off of the stroke of the holding mechanism 3 and the like. That is, the closer the focal point O is to the ZP (zone plate) element 2, the finer the diffraction pattern is required. The farther the focal point O is from the ZP (zone plate) element 2, the greater the stroke required for the holding mechanism 3. The holding mechanism 3 is adjusted so that the vertex of the test surface 13a coincides with the light condensing position, and the position of the test lens 13 is adjusted. Also,
As in the case of the interference measurement, the position of the test lens 13 in the optical axis X direction is measured by the detection device 7 and stored in the arithmetic device 200.

Next, based on the measurement values obtained by the detection device 7 stored in the calculation device 200, the displacement amount L1 of the test lens 13 in the optical axis X direction at the time of interference measurement and at the time of vertex reflection is calculated. Subsequently, f
An operation of substituting (L1−L0) and the measured ΔW1 into Expression (1) is performed, and thereby ΔW0 is calculated. Note that L0 and the function f required for the calculation of the equation (1) are stored in the calculation device 200 in advance.

In the above description, the interference measurement of the test surface 13a is performed before the alignment operation using the vertex reflection. However, the alignment operation may be performed before the interference measurement.

Second Embodiment A second embodiment of the aspherical shape measuring apparatus according to the present invention will be described below with reference to FIG. The apparatus according to the second embodiment attempts to use a so-called null lens and a ZP (zone plate) element in place of a ZP (zone plate) element alone as a mechanism for generating a measurement null wavefront and a spherical wave for alignment. It is a thing.

As shown in FIG. 4A, in the second embodiment, a high-precision reference surface 101 is provided on a Fizeau flat 101.
a, and a concentric diffraction grating pattern 101b for alignment around the high-precision reference surface 101a.
Is formed. Further, a null lens 102 is used to obtain a measurement null wavefront.

As shown in FIG. 4A, a plane wave emitted from an interferometer main body (not shown) is applied to a Fizeau flat 101.
Is incident perpendicularly on the high-precision reference surface 101a, thereby generating one measurement wavefront (reflected light) for forming interference fringes. The measurement light beam transmitted through the high-precision reference surface 101a is incident on the null lens 102, and generates a measurement null wavefront 110 having an aspherical shape substantially equivalent to the designed shape at a predetermined position.

On the other hand, the spherical wave generated by being diffracted by the concentric diffraction grating pattern 101b provided outside the effective area of the Fizeau flat 101 is converged toward the focal point O so as not to interfere with the null lens 102. In this case, since the angle of the light exiting the diffraction pattern 101b with respect to the optical axis X can be set small, the diffraction grating pattern 10b
1b is easy to manufacture.

Note that the point at which the displacement of the lens 13 to be measured is measured by the detection device is the same as in the first embodiment, and the shape of the surface 13a to be measured is measured in the same procedure as in the first embodiment. can do.

In the second embodiment, the Fizeau flat 1
Although the diffraction grating pattern 101b is formed in FIG. 01, as shown in FIG. 4B, a ZP (zone plate) element 14 in which a diffraction grating pattern 14a is formed separately from the Fizeau flat 101A is used. May be converted into a spherical wave by a ZP (zone plate) element 14. In this case, since the diffraction grating pattern can be created separately from the ZP (zone plate) element, there is an advantage that the fabrication is easy and the degree of freedom of the optical arrangement is increased.

Third Embodiment Hereinafter, a third embodiment of an aspherical surface measuring apparatus according to the present invention will be described with reference to FIG.
An embodiment will be described. In the third embodiment,
A parabolic mirror is used as a generation mechanism of a reference wavefront (spherical wave).

As shown in FIG. 5, the main body of the interferometer (not shown)
Is incident perpendicularly on the high-precision reference surface 201a of the Fizeau flat 201 to generate one measurement wavefront (reflected light) for forming interference fringes. The measurement light beam transmitted through the high-precision reference surface 201a is
02, and generates a measurement null wavefront 210 having an aspherical shape substantially equivalent to the designed shape at a predetermined position.

On the other hand, the luminous flux outside the effective measurement area of the Fizeau flat 201 is reflected on the parabolic mirror 1 disposed outside the null lens.
5, and is converted into a spherical wave which is focused on the focal point O of the paraboloid. FIG. 5 shows a case where an arrangement is adopted in which the focal point O of the parabolic mirror 15 coincides with the vertex of the test lens 13 at a predetermined position of the null measurement (a measurement position at which the interference fringes are substantially one color). However, by providing the moving mechanism 16 for moving the parabolic mirror 15 in the measurement optical axis X direction, correction is made even when the relative positional relationship between the null measurement wavefront 210 and the parabolic mirror 15 is affected by drift or the like. Becomes possible. As shown in FIG. 5, the moving mechanism 16 includes, for example, a holding part 16a for holding the parabolic mirror 16, and a sliding part 16b that comes into contact with the holding part 16a.
And a rail portion 16c that supports the sliding portion 16b so as to be slidable in the measurement optical axis X direction.

As in the first embodiment, the test lens 1
The position in the measurement optical axis X direction of No. 3 is measured by the detection device. Further, the shape of the test surface 13a can be measured by the same procedure as in the first embodiment. However, in the third embodiment, since the parabolic mirror 15 is used, there is little restriction on the positional relationship between the parabolic mirror 15 and the focal point O. That is, it is possible to generate a spherical wave having a large irradiation angle with respect to the optical axis X. By moving the parabolic mirror 15, the focal point O can be set at an arbitrary position. Therefore, the present invention can be applied to the case where the value of L1 shown in FIG. 1 is “0”, that is, the case where the test lens 13 is not moved.

In the third embodiment, the measurement null wavefront 21
Null lens 102 as a null element for generating 0
However, a zone plate may be used instead of the null lens 102.

[0041]

As described above, according to the present invention,
Measurement is performed based on the measured surface shape data obtained from the interference fringe when the measured object is set at the planned measurement position and the positional displacement between the planned measurement position and the alignment position detected by the displacement detecting means. Since the shape of the surface is calculated,
It can be applied to shape measurement of a wide range of aspherical shapes.

[Brief description of the drawings]

FIG. 1 is a diagram showing the principle of an aspherical shape measuring device according to the present invention.

FIG. 2 is a block diagram showing an aspherical surface shape measuring device according to the first embodiment.

FIG. 3 is a diagram showing an optical system device of the aspherical shape measuring device according to the first embodiment.

FIGS. 4A and 4B are diagrams illustrating an aspherical shape measuring apparatus according to a second embodiment and a modified example, in which FIG. 4A illustrates the apparatus according to the second embodiment, and FIG. FIG.

FIG. 5 is a diagram illustrating an aspherical surface shape measuring apparatus according to a third embodiment.

[Explanation of symbols]

 Reference Signs List 2 ZP (zone plate) element 3 Holding mechanism 7 Detector 10 Measurement null wavefront 11 Spherical wave 13 Test lens 13a Test surface 102 Interferometer main body 200 Computing device O Focus

Claims (1)

[Claims] 1. An aspherical shape measuring device for measuring an aspherical shape of a surface to be measured formed on an object to be measured, comprising: an interferometer main body for forming an interference fringe based on mutual interference between a reference light and a measuring light; A null element for converting a wavefront of light emitted from the interferometer main body into an aspherical wave having substantially the same shape as the surface to be measured; and focusing the wavefront of light emitted from the interferometer main body toward a focal point. A conversion element for converting the surface to be measured into a spherical wave to be formed; a measurement position to be irradiated with the aspherical wave having a shape substantially equal to the surface to be measured via the null element on the surface to be measured; and a conversion element formed by the conversion element. Holding means for movably holding the object to be measured between the focal point of the spherical wave and an alignment position at which the vertex of the surface to be measured coincides with the focal point; and a positional displacement amount between the planned focal position and the alignment position. Detect When the object to be measured is set at the predetermined measurement position by the displacement amount detecting means and the holding means, the object is obtained from interference fringes due to mutual interference between the reference light and the measuring light obtained by reflection on the surface to be measured. An aspherical shape measuring apparatus, comprising: calculating means for calculating a shape of the measured surface based on measured surface shape data and the displacement detected by the displacement detecting means.