JPH11337306A - Interference measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an interference measuring device to remove a gravity strain when absolute calibration of an optical face inclined to gravity is done by absolutely calibrating a dummy face region, which covers a face to be inspected of a given attitude and correctly faces the gravity, using together with an absolute calibration means by an apex reflection. SOLUTION: A parallel light 5 is converted to a measuring light 6 of a spherical surface wave by an interference optical systems 1 and a sphere center of a dummy face 2a of a dummy body 2 which is equivalent to a face to be inspected 3a is coincided with a light focus point of the interference optical system 1. Thereby, reflected lights of measuring lights from a reference face 1a and the dummy face 2a form an interference fringe on a detector built in an interference meter body to enable an interference measuring. Then, when the dummy face 2a is inscribed at a bottom face of a cone where a gravity axis g is regarded as a rotation symmetry axis, setting is done so that a solid angle thereof covers a solid angle formed by an face to be inspected 3a which is a sum of sets rotated the face to be inspected 3a around the gravity axis g and an absolute calibration is done by an absolute calibration means used the measuring light 6 of a Fizeau lens and apex reflection of the dummy face 2a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer capable of eliminating an error caused by gravity when performing absolute calibration of the surface accuracy of an optical surface.

[0002]

2. Description of the Related Art FIG. 8A shows an arrangement diagram of a general interference measurement. That is, first, the parallel light 5 emitted from an interferometer body (not shown) is converted into a spherical wave measurement light 6 by the interference optical system 1.
Then, the center of the dummy surface (spherical surface) 2a, which is the measured surface, of the dummy body 2 that is the object to be measured is matched with the converging point of the interference optical system 1 so that the interference optical system The reflected light of the measurement light from each of the reference surface 1a and the dummy surface 2a forms interference fringes on a detector built in the interferometer body, thereby enabling interference measurement.

The interference fringes are formed by a reference surface 1a and a dummy surface 2a.
Since the sphericity errors are superimposed and measured, so-called absolute calibration is performed to separate them. If the surface to be measured is spherical, its surface accuracy (spherical if spherical,
Does not include the error of the radius of curvature defined by the optimal approximation sphere)
As a practical method of absolutely calibrating the method, a method using vertex reflection (Appl. Opt., 13, 2693/197) is used.
4) and a wavefront creation extraction method (Japanese Patent Laid-Open No. 4-027111) are known.

[0004] On the other hand, when measuring the surface to be measured of an object to be measured by interference, it is a rule that the posture of the object to be measured is maintained in a state where the object is actually used. If it is required to absolutely calibrate the deviation (sphericity) from the design value of the surface to be measured, a distorted state caused by gravity due to the holding of the measurement target (hereinafter, referred to as
(Referred to as "gravitational distortion").

FIG. 8A shows the optical axis of the dummy surface 2a (usually the object to be measured) when the direction of falling through the converging point of the interference optical system 1 by the action of gravity is defined as the gravity axis "g". The optical element, which is an object, adopts a rotationally symmetric outer shape like a lens, and it is common to cut a spherical surface with a spherical center on its rotationally symmetric axis by a cylinder, and use a part of the spherical surface as an optical effective surface. Therefore, the outer periphery of the surface to be measured is also circular, and the optical axis is defined as the central axis of the outer diameter.) The dummy body is used in a state where the optical axis 7 is inclined with respect to the gravity axis g (perpendicular to the figure). This is assumed to be performed.

In FIG. 8B, which is a view taken in the direction of the arrow in FIG. 8A, the dummy body is supported symmetrically with respect to gravity by the support member 8, and a general support is provided together with the belt suspension. Is the way. At this time, the gravitational distortion also appears in a symmetrical shape as represented by “A” in FIG. Although this symmetry breaks depending on the supporting method, directional gravitational distortion due to gravity is inevitable in any supporting method.

[0007]

However, when an attempt is made to apply the above-described absolute calibration method, FIG.
In a state where the dummy surface 2a interferes with the reference surface 1a as shown in FIG.
An operation for rotating the dummy body 2 about the optical axis 7 of the dummy surface 2a is required. In FIG. 8B, ● represents the 0-degree direction based on the rotation of the dummy body 2. Y axis is optical axis 7
Is taken in the direction opposite to the gravity when Z is the Z axis.

[0008] Among the absolute calibration methods, the method using vertex reflection requires an operation of rotating the dummy body 2 around the optical axis 7 by 180 degrees. FIG. 8C shows the result, and the rotation of the dummy body 2 is shown at the position of ●. However, the gravitational distortion A does not follow the rotation of the dummy body 2 and remains as a bias of the measurement light 6, and as a result, an error may be superimposed on the measurement data of the sphericity of the surface to be measured in the use state. It was inevitable.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and provides an interference measurement apparatus capable of eliminating gravitational distortion when performing absolute calibration of the surface accuracy of an optical surface inclined with respect to gravity. With the goal.

[0010]

According to the present invention, in order to achieve the above object, as a first means, a test surface of a test object having a given posture and capable of performing interference measurement with converging measurement light is provided. To cover the “union of the test surfaces formed when the test subject is rotated about the axis of gravity passing near the convergence position of the measurement light”, which is equivalent to the test surface. A dummy body having a dummy surface, an interference optical system that generates measurement light capable of measuring interference in a region corresponding to the union of the dummy surfaces, and a vicinity of a convergence position of the measurement light without changing a posture with respect to gravity. An interferometer having rotation means for rotating the dummy body relative to the interference optical system about a passing gravity axis is used. Thus, the area of the dummy surface facing the gravity, which covers the surface to be inspected in the given posture, is absolutely calibrated by using the absolute calibration method using vertex reflection in combination, so that the object in the arbitrary posture can be measured. Absolute calibration of the inspection surface is also possible.

As a second means, a dummy body having a dummy surface equivalent to a test surface of a test subject having a given posture and an interference measurement of the test surface can be performed. An interference optical system that generates converging measurement light, and a reflector having a reflection surface for deflecting the measurement light arranged near the convergence position of the measurement light are provided so that interference measurement of the dummy surface can be performed. An interferometer that is arranged with a correlation is used. Thus, by absolutely calibrating the interference optical system facing the test surface in an arbitrary posture through the reflecting surface using the dummy surface facing the gravity, the test surface in the arbitrary posture can be interposed through the reflector. It is possible to perform absolute calibration without the need.

As a third means, an interference optical system for generating convergent measurement light capable of measuring interference of the test surface with respect to the test surface of the test subject in a given posture; And a reflector having a reflection surface for deflecting the measurement light disposed in the vicinity of the convergence position of the measurement surface, and using an interference measurement device disposed with a correlation so that interference measurement of the surface to be measured can be performed. did. This makes it possible to absolutely calibrate the test surface in an arbitrary posture via the reflection surface by using the interference optical system directly facing gravity.

As a fourth means, a dummy body having a dummy surface equivalent to the test surface with respect to the test surface of the test subject in a given posture is provided. An interference optical system that generates convergent measurement light capable of interferometry and a reflector having a reflection surface disposed near the convergence position of the measurement light and for deflecting the measurement light, An interferometer that is arranged with a correlation so as to be able to selectively perform the interference measurement of the “surface and the dummy surface” is used. Thus, by absolutely calibrating the interference optical system in an arbitrary posture through the reflecting surface using the dummy surface facing the gravity, the test surface in the arbitrary posture can be absolutely calibrated through the reflecting surface. It becomes possible.

A fifth means is to rotate the dummy body relatively to the interference optical system around a gravity axis passing near the convergence position of the measurement light without changing the attitude with respect to gravity. Means is provided, and an interference measuring device for controlling the reflector in correlation with the rotating means so as to enable interference measurement of the dummy surface is used. Thus, by absolutely calibrating the interference optical system in an arbitrary posture via the reflecting surface using the dummy surface in the arbitrary posture, it becomes possible to absolutely calibrate the test surface in the arbitrary posture.

A sixth means is to rotate the subject relatively to the interference optical system around a gravity axis passing near the convergence position of the measurement light without changing the attitude with respect to gravity. And an interferometer for controlling the reflector so as to be correlated with the rotating means so that interference measurement of the surface to be detected can be performed. This makes it possible to absolutely calibrate the test surface in any orientation through the reflective surface by absolutely calibrating the interference optical system in any orientation through the reflective surface using the test surface in any orientation. Becomes

As a seventh means, "the reflector can be freely controlled or the reflection of the reflection surface can be performed so that" the interference measurement of the dummy surface, the test surface, or the interference optical system "can be performed. An interferometer that selectively sets the rate is used. This makes it possible to increase the content and the degree of freedom when absolutely calibrating the test surface in an arbitrary posture.

As an eighth means, an interferometer that corrects phase data of interference fringes obtained by the interferometry with the angular characteristics of the reflection surface is used. This makes it possible to increase the accuracy of absolute calibration of the test surface. In the meantime, 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 for easy understanding of the present invention. It is not limited.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment of Interference Measuring Apparatus According to the Present Invention Hereinafter, a first embodiment of an interference measuring apparatus according to the present invention will be described with reference to FIG. The first embodiment does not use a reflector. In FIG. 1, a parallel light 5 emitted from an interferometer body (not shown) is converted into a measurement light 6 of a spherical wave by an interference optical system 1, and then a test surface 3 a of a subject 3 which is a measurement object A dummy body 2 having a (conjugated) dummy surface 2a equivalent to (the thick line in the figure) is prepared,
By making the spherical center of the dummy surface coincide with the converging point of the interference optical system 1, the reference surface of the interference optical system 1 (the Fizeau surface which is the final surface when a Fizeau lens is used in the interference optical system) 1a and the dummy The reflected light of the measurement light from each of the surfaces 2a forms interference fringes on a detector built in the interferometer main body, thereby enabling interference measurement.

At this time, when the dummy surface 2a is inscribed at the bottom surface of a cone whose rotational symmetric axis is the gravity axis g (which passes through the converging point of the interference optical system 1 as described above), the solid angle of the cone Covers the solid angle of the test surface 30a, which is a union of the test surface 3a rotated about the gravitational axis g, such that the reference surface 1a and the dummy surface 2a have an NA (numerical aperture). ) Is set.

Then, in this state, the measuring light 6 (equivalent to the reference surface 1a) and the dummy surface 2a of the Fizeau lens are absolutely calibrated using the above-mentioned vertex reflection by using a rotating means and a reflector (not shown). Absolute calibration It should be noted that the area where the absolute calibration of the measured surface under the gravitational distortion is possible is limited to the region conjugate with the measured surface 30a in FIG.

Finally, the spherical center of the test surface 2a is
If the subject 2 is set in a state where the subject 2 is actually used as shown in the figure, as long as the measurement light 6 does not change, the test surface of the subject 3 in a desired posture is not changed. Absolute calibration of 3a becomes possible. When it is necessary to consider the change in the wavefront of the measurement light 6, it is desirable that the radius of curvature of the test surface and that of the dummy surface, including the unevenness, be matched.

When the wavefront generation extraction method is used as the absolute calibration method, the calibration object that is not affected by gravity distortion is limited to the non-rotationally symmetric component of the dummy surface. However,
Applicable even if the dummy surface is an aspheric surface, and the concept of this reflex subtraction (an interferometric measurement method for measuring the test surface with high accuracy via a reference surface based on a separately accurately calibrated reflex). Is also applicable to off-axis aspheric surfaces. In other words, the dummy surface may be replaced with a base (on-axis) aspheric surface serving as a reference for reflex subtraction, and the test surface 2a may be replaced with an off-axis aspheric surface.

Second Embodiment of Interference Measuring Device According to the Present Invention Hereinafter, a second embodiment of the interference measuring device according to the present invention will be described with reference to FIG. The second embodiment is an embodiment using a reflector. In FIG. 2, a reference surface 1a and a dummy surface 2a that cover the NA of the test surface 3a of the subject are prepared, the reference surface and the test surface maintain a conjugate positional relationship, and the reference surface and the dummy surface are maintained. Are arranged so as to maintain a conjugate positional relationship via the reflecting surface 4a of the reflector 4, thereby enabling interference measurement. The test surface and the reference surface face each other, and the dummy surface faces the gravity axis g.

In all the drawings including FIG. 2, the subject, the Fizeau lens, and the dummy body (reference for Lev subtraction)
, "W" and "F"
It is represented by "R". Further, in all the embodiments using the reflector, the reflecting surface is used to make the XY in FIG.
Since the coordinates are subjected to transformation such as inversion, attention must be paid to the consistency of the coordinates when performing the subtraction.

As a measurement procedure, first, the reference surface 1a is set so as to face the subject W in a state of being actually used. Next, the reference surface 1a is absolutely calibrated by performing the interference measurement of the reference surface 1a via the reflection surface 4a using the dummy surface 2a which has been absolutely calibrated in a state facing the gravity.
Finally, the reflector 4 is removed (in the case of a convex test surface as shown by the dotted line in the figure, it is not always necessary to remove the reflector), and the test object W is supported in an actually used state, and the test surface 3a Is subjected to interference measurement by directly facing the reference surface 1a, thereby absolutely calibrating the test surface 3a.

-First Modification of Second Embodiment of Interference Measuring Device According to the Present Invention- Hereinafter, a first modification of the second embodiment of the interference measuring device according to the present invention will be described with reference to FIG. Will be described. In FIG. 3, the NA of the test surface 3a of the subject is covered.
The interference measurement is enabled by preparing the reference surface 1a and arranging the reference surface and the test surface so as to maintain a conjugate positional relationship via the reflection surface 4a of the reflector 4. Note that the reference surface is directly opposed to the gravity axis g.

The measuring procedure is as follows. First, the reference surface 1a, which has been absolutely calibrated while facing the gravity, is used for the reflection surface 4a.
By performing the interference measurement of the test surface 3a via a, the test surface 3a is absolutely calibrated. -Second Modification of Second Embodiment of Interference Measuring Device According to the Present Invention-Hereinafter, a second modification of the second embodiment of the interference measuring device according to the present invention will be described with reference to FIG. .

In FIG. 4A, a reference surface 1a and a dummy surface 2a are provided to cover the NA of the test surface 3a of the subject, and the reference surface and the dummy surface are the reflection surfaces of the reflector 4. By arranging them so as to maintain a conjugate positional relationship via 4a, interference measurement is enabled. Note that the dummy surface is directly opposed to the gravity axis g. In FIG. 4B, the reference surface and the surface to be measured are reflection surfaces 4 of the reflector 4.
By arranging so as to selectively maintain a conjugated positional relationship via “a”, interference measurement is enabled. The reference plane is
It is arranged in an appropriate posture at a position where interference measurement via the reflection surface is possible.

The measurement procedure is as follows. First, an interference measurement of the reference surface 1a is performed via the reflecting surface 4a using the dummy surface 2a which has been absolutely calibrated in a state facing the gravity.
The reference plane 1a is absolutely calibrated. Next, the subject W is supported in a state where it is actually used, and the reflector 4 is selectively disposed.
By performing interference measurement of the test surface 3a via the reflection surface 4a, the test surface 3a is absolutely calibrated.

Third Embodiment of Interference Measuring Device According to the Present Invention Hereinafter, a third embodiment of the interference measuring device according to the present invention will be described with reference to FIG. The third embodiment is an embodiment in which a rotating unit is used together with a reflector. In FIG. 5A, a reference surface 1a and a dummy surface 2a that cover the NA of the test surface 3a of the subject are prepared, the reference surface and the test surface maintain a conjugate positional relationship, and the reference surface is maintained. And the dummy surface are arranged so as to maintain a conjugate positional relationship via the reflection surface 4a of the reflector 4, thereby enabling interference measurement. The test surface and the reference surface face each other.

FIG. 5B shows that the dummy body R is rotated (reversed) by 180 degrees around the gravitational axis g by rotating means (not shown), and the reference surface and the dummy surface are changed to the reflecting surface 4a of the reflecting member 4. Interference measurement is possible by controlling the reflector 4 in conjunction with the rotating means so as to maintain a conjugate positional relationship through the intermediary. As a measurement procedure, first, the reference surface 1a is set so as to face the subject W in a state of being actually used. Next, by using the dummy surface 2a and performing interference measurement of the reference surface 1a via the reflection surface 4a in the two arrangements shown in the figure, 0-degree data for absolute calibration of the reference surface 1a and 180-degree data are obtained. Obtain inverted data. Further, the data of the vertex reflection of the reference surface 1a is obtained by using a “reflector not shown” equivalent to the reflector 4. From these three data, the reference plane 1a
Absolute calibration becomes possible. Finally, the test object W is supported in a state where it is actually used, and the test object 3 is supported without the reflection surface 4a.
By performing interference measurement with “a” facing the reference surface 1a, the test surface 3a is absolutely calibrated.

When the wavefront creation extraction method is used, 0
In this case, n pieces of circumferentially equally divided data are obtained instead of two pieces of data of 180 degrees and 180 degrees. From these n data, the absolute calibration of the non-rotationally symmetric component of the reference surface 1a becomes possible. -First Modification of Third Embodiment of Interference Measuring Device According to the Present Invention- Hereinafter, a first modification of the second embodiment of the interferometer according to the present invention will be described with reference to FIG. .

In FIG. 6 (a), a reference surface 1a covering the NA of the test surface 3a of the subject is prepared, and the reference surface and the test surface are conjugated via the reflection surface 4a of the reflector 4. By arranging them so as to maintain a proper positional relationship, interference measurement is possible. The optical axis of the reference surface may be inclined with respect to the gravity axis g. FIG. 6B shows that the subject W is rotated (reversed) by 180 degrees around the gravitational axis g by rotating means (not shown), and the reference surface and the test surface are reflected by the reflection surface 4 of the reflector 4.
Interference measurement is possible by controlling the reflector 4 in conjunction with the rotating means so as to maintain a conjugate positional relationship via a.

The procedure of the measurement is as follows.
By performing interference measurement of the reference surface 1a via the reflection surface 4a, 0 degree data for absolute calibration of the reference surface 1a and 1
80-degree inverted data is obtained. Further, the data of the vertex reflection of the reference surface 1a is obtained by using a “reflector not shown” equivalent to the reflector 4. From these three data, the absolute calibration of the reference surface 1a becomes possible, and at the same time, the absolute calibration of the inspection surface 3a is completed.

When the wavefront generation extraction method is used, it is the same as in the third embodiment. -Second Modification of Third Embodiment of Interference Measuring Device According to Present Invention-Hereinafter, a second modification of the third embodiment of the interference measuring device according to the present invention will be described with reference to FIG. . FIG.
In (a), a reference surface 1a and a dummy surface 2a that cover the NA of the test surface 3a of the subject are prepared,
By arranging the reference surface and the dummy surface so as to maintain a conjugate positional relationship via the reflection surface 4a of the reflector 4, interference measurement can be performed.

FIG. 7B shows that the dummy body R is rotated (reversed) by 180 degrees around the gravitational axis g by rotating means (not shown), and the reference surface and the dummy surface are changed to the reflecting surface 4 a of the reflecting member 4. Interference measurement is possible by controlling the reflector 4 in conjunction with the rotating means so as to maintain a conjugate positional relationship through the intermediary. As a measurement procedure, first, the reference surface 1a is set so as to face the subject W in a state of being actually used. Next, by using the dummy surface 2a and performing interference measurement of the reference surface 1a via the reflection surface 4a in the two arrangements shown in the figure, 0-degree data for absolute calibration of the reference surface 1a and 180-degree data are obtained. Obtain inverted data. Further, the data of the vertex reflection of the reference surface 1a is obtained by using a “reflector not shown” equivalent to the reflector 4. From these three data, the reference plane 1a
Absolute calibration becomes possible. Finally, the subject W is supported in a state where it is actually used, and the reflector 4 is selectively disposed,
By performing interference measurement of the test surface 3a via the reflection surface 4a, the test surface 3a is absolutely calibrated.

Note that the posture of the test surface and the dummy surface is the same,
For example, when it is said that only the radius of curvature is different, it is not necessary to selectively dispose the reflector. When the wavefront creation extraction method is used, it is the same as in the third embodiment. -Fourth embodiment of the interferometer according to the present invention-In the fourth embodiment, in the second and third embodiments, the reflector is selectively arranged and rotated. In addition to "correlation with the means", the position can be freely controlled so as to obtain interference fringes, or the reflectance of the reflecting surface can be selectively changed.

Thus, in the second embodiment, the absolute calibration of the rotationally symmetric component of the surface to be measured can be performed by applying the wavefront creation extraction method. As a specific control of the reflector, the reflector in the state shown in FIGS. 2 to 4 is caused to perform a so-called “miso sipping” motion about the normal passing through the light condensing point. The same movement is possible by rotating around the normal line in a state where the focusing point is tilted from the state in FIG. Thus, lateral displacement in multiple directions can be equivalently performed without changing the attitude of the surface to be measured with respect to gravity. The procedure for extracting the rotationally symmetric component has been disclosed in Japanese Patent Application No. 7-049749.

In the third embodiment, when the wavefront creation extraction method is applied, only the reflector 4 is appropriately controlled in a state where the rotating means is stopped. 5 to 7 from the state shown in FIGS. 5 to 7 around the focal point, the lateral displacement in one direction can be equivalently performed without changing the attitude of the surface to be measured with respect to gravity. Conversely, by giving a rotation to the surface to be measured by the rotating means while the reflector 4 is fixed, the same lateral displacement can be performed in one direction. In the third embodiment, since a non-rotationally symmetric component has already been extracted, it is possible to extract a rotationally symmetric component only by performing a lateral shift in one direction using this.

In the third embodiment, when an absolute calibration method using vertex reflection is applied, the reflector 4 is directly and appropriately replaced with a “not shown reflector” equivalent to the reflector 4. Specifically, the reflector is tilted from the state shown in FIGS. 5 to 7 around the focal point to face the interference optical system, thereby obtaining the vertex reflection data of the surface to be measured. It becomes possible.

In order to obtain interference fringes with good contrast, the reflectance of the reflecting surface of the "reflector not shown" is substantially the same as the reflectance of the surface to be measured when obtaining the vertex reflection data of the surface to be measured. On the other hand, it is desirable to set the value to a value, but when performing normal interference measurement via the reflective surface, it is desirable that the reflectance of the reflective surface 4a of the reflector 4 be 100%. Therefore, with respect to the reflection surface 4a, the reflectance of the mirror surface (10%) is equal to the reflectance of the measured surface (about 4% in the case of a glass surface).
By providing a plurality of regions set so that the selection can be made “stepwise or continuously” up to the reflectance of (close to 0%), it is possible to easily obtain the vertex reflection data of the surface to be measured Becomes

Further, in the third embodiment, a case where the surface to be measured, which is an aspheric surface, is absolutely calibrated by using the absolute calibration method using the apex reflection together with the wavefront synthesis (Japanese Patent Application No. Hei 8 (1996) -108).
-239369), it is possible to obtain the data of the apex reflection of the surface to be measured by further moving the reflector back and forth in the optical axis direction of the interference optical system from the state directly facing the interference optical system described above. Become.

Fifth Embodiment of Interference Measuring Apparatus According to the Present Invention A fifth embodiment is different from the second to fourth embodiments in that it is obtained by the ordinary interference measurement through the reflecting surface. This is a mode in which phase data of interference fringes obtained can be corrected based on the angle characteristics of the reflection surface. Accordingly, for example, even when the phase data of the interference fringes has an apparent error due to the angular characteristics of the reflection surface, if the spectral angle characteristics of the reflection surface near the focusing point are grasped and set, the interference fringes can be obtained. Can be corrected. If the NA of the surface to be measured is large and the dependence of the spectral angle characteristic on the incident angle cannot be ignored, this correction is essential.

The correction of the angle characteristic can be widely applied to interference measurement using vertex reflection, and is also effective for, for example, three-plane alignment on a spherical surface (Japanese Patent Laid-Open No. 1-244306).

[0045]

As described above, by employing the interferometer according to the present invention, it is possible to perform absolute calibration of a surface to be measured having an arbitrary posture regardless of whether it is a spherical surface or an aspherical surface.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment according to the present invention.

FIG. 2 is an explanatory diagram of a second embodiment according to the present invention.

FIG. 3 is an explanatory diagram of a first modified example of the second embodiment according to the present invention.

FIG. 4 is an explanatory diagram of a second modification of the second embodiment according to the conventional example.

FIG. 5 is an explanatory diagram of a third embodiment according to a conventional example.

FIG. 6 is an explanatory diagram of a first modified example of the third embodiment according to the present invention.

FIG. 7 is an explanatory diagram of a second modification of the third embodiment according to the conventional example.

FIG. 8 is an explanatory diagram of a conventional example.

[Explanation of symbols]

 1 ... Interference optical system 1a ... Reference surface 2 ... Dummy body 2a ... Dummy surface 3 ... Subject 3a ... Test surface 4 ... Reflection Body 4a Reflecting surface 5 Parallel light emitted from interferometer 6 Measurement light 7 Optical axis of measured surface 8 Support member 9・ Gravity distortion

Claims (11)

[Claims] 1. A method according to claim 1, wherein the object having a given posture has a center on a gravity axis passing near a convergence position of the measurement light. And a dummy body having a dummy surface equivalent to the test surface, which covers the union of the test surface formed when the is rotated, and an interference measurement of an area corresponding to the union of the dummy surface. The dummy body is rotated relative to the interference optical system around an interference optical system that generates a measurement light capable of being driven, and a gravity axis passing near the convergence position of the measurement light without changing the attitude with respect to gravity. An interferometer having a rotating means for rotating the interferometer. 2. A dummy body having a dummy surface equivalent to a test surface of a test subject having a given posture, and a convergent measuring beam capable of measuring interference of the test surface. And a reflector having a reflection surface for deflecting the measurement light, which is disposed near the convergence position of the measurement light, is correlated so that interference measurement of the dummy surface can be performed. An interference measurement device characterized by being arranged in a position. 3. An interference optical system for generating converging measurement light capable of measuring the interference of the test surface with respect to the test surface of the test subject having a given posture, and a vicinity of a convergence position of the measurement light. And a reflector having a reflection surface for deflecting the measurement light, which is disposed in the apparatus, with a correlation so that interference measurement of the surface to be measured can be performed. 4. An interference measurement of a dummy body having a dummy surface equivalent to the test surface with respect to the test surface of the test subject having a given posture and “the test surface and the dummy surface” An interference optical system that generates convergent measurement light, and a reflector having a reflection surface disposed near the convergence position of the measurement light for deflecting the measurement light are referred to as `` the test surface, and the An interference measurement apparatus characterized in that correlation is provided so that interference measurement of a "dummy surface" can be selectively performed. 5. A rotating means for rotating the dummy body relative to the interference optical system around a gravity axis passing near the convergence position of the measurement light without changing the attitude with respect to gravity, The interference measuring apparatus according to claim 2, wherein the reflector is controlled so as to have a correlation with the rotating means so that interference measurement of the dummy surface can be performed. 6. A rotation means for rotating the subject relatively to the interference optical system around a gravity axis passing near the convergence position of the measurement light without changing the attitude with respect to gravity, 4. The interference measurement apparatus according to claim 3, wherein the reflector is controlled so as to have a correlation with the rotating means so that interference measurement of the test surface can be performed. 7. The reflector can be freely controlled so that interference measurement of the “dummy surface, the test surface, or the interference optical system” can be performed, or the reflectance of the reflection surface can be selected. The interferometer according to claim 2, wherein the interferometer is set in a specific manner. 8. The interference measurement apparatus according to claim 2, wherein phase data of interference fringes obtained by the interference measurement is corrected based on an angle characteristic of the reflection surface. 9. The interferometer according to claim 1, wherein the surface to be measured is a spherical surface. 10. The interferometer according to claim 1, wherein the surface to be measured is an off-axis aspherical surface, and the dummy surface is an on-axis aspherical surface. 11. The interferometer according to claim 2, wherein the test surface is an aspheric surface.