JPH0682229A - Method and apparatus for measuring wave front aberration of specimen with anamorphic shape - Google Patents

Abstract

PURPOSE:To obtain a method and means which enable the obtaining of wave front information also including internal information of a specimen in a method for measuring the accuracy of the specimen by irradiating the object to be measured and a reference surface to be a reference with light allowing interference from the same light source to generate an interference fringe being overlapped with return light therefrom. CONSTITUTION:A reference surface 14 and a specimen 5 are irradiated with light allowing interference from a light source and the reflected light from the control surface is made to overlap the light transmitted through the specimen 5 to generate a one cross-section interference fringe on an image sensor 10. The cross-section interference fringe is analyzed to determine a front wave aberration. The reference surface 14 and the specimen 5 are moved and the front wave aberrations of the respective one cross-sections of the specimen are put together to obtain a total front wave aberration of the entire surface of the specimen 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring wavefront aberration of an object having an anamorphic shape.

[0002]

2. Description of the Related Art An apparatus for irradiating an object to be measured and a reference surface serving as a reference with coherent light from the same light source, and superimposing return light from these to form interference fringes to measure the accuracy of the object to be inspected. In the above, a BTS measuring machine has been proposed as a device for measuring the surface of a test object.

Here, BTS is an abbreviation for barrel toroidal surface. As shown in FIG. 7, when the main diameter lines orthogonal to each other at vertices and the respective radii of curvature of these main diameter lines are different, one of the main diameters is used. A line is a surface formed by making a line a busbar (hereinafter referred to as "G main radial line") and rotating this along the other main radial line (hereinafter referred to as "R main radial line"). In other words, it can be said that it is formed by rotating the G main diameter line around the rotation axis OO.

If these major diameter lines are equal, it becomes a normal spherical lens, and if one radius of curvature is infinite, it becomes a cylinder lens.

In this regard, the applicant of the present application has filed Japanese Patent Application No. 2-
No. 126659 proposes a method for measuring a toroidal surface of donut type or normal type. Also, in Japanese Patent Application No. 3-050104 by the same applicant, the G main diameter line is long and R
A method for measuring a barrel-shaped toroidal surface or a saddle-shaped toroidal surface with a short main diameter line is proposed.

In the conventional BTS measuring machine or measuring method,
The coherent light emitted from the light source is converted into parallel light of an appropriate size by the beam expander, and is incident on the objective lens.
The final surface of this objective lens is a half mirror having a certain curvature, and even if a part of the incident light is reflected, it returns to the optical path occasionally.

Further, the wavefront of the reference light that has passed through the objective lens is a spherical wave and is condensed at one point. It is assumed that the test lens is arranged in front of this condensing point. In this case, if the center of curvature of the lens to be inspected and the center of curvature of the wavefront of the reference light coincide with each other, the reflected light from the surface of the lens to be inspected returns to the original optical path.

The return light from the lens to be inspected contains information on the unevenness of the surface of the lens to be inspected as disturbance of the wavefront.

On the other hand, when the reference light and the return light from the objective lens overlap, interference fringes are generated. If there is no unevenness on the surface of the lens to be inspected, the obtained interference fringe will be pure white or pure black. Actually, for analysis, the test surface is slightly tilted to generate equal-thickness interference fringes. The slit-shaped elongated interference fringes thus generated are detected by a one-dimensional CCD or the like and analyzed by the Fourier transform method to obtain surface accuracy information.

[0010]

[Problems to be Solved by the Invention]
The TL measuring device is intended to measure the surface accuracy of a flat cylinder surface, a barrel toroidal surface, or the like, which is an object to be inspected. Internal information of the object to be inspected, for example, bubbles inside the object to be inspected, striae, etc. However, it is impossible to obtain measurement information including nonuniformity in a transparent medium.

Therefore, it is an object of the present invention to provide a measuring method and means capable of obtaining wavefront information in consideration of internal information of an object to be inspected.

[0012]

In order to achieve the above object, the present invention has any one of the following configurations.

(1). A step of irradiating the reference surface and the test object with coherent light from a light source, and superimposing the reflected light from the reference surface and the light transmitted through the test object to generate a one-section interference fringe, and the one-section interference The step of analyzing the fringes to obtain the wavefront aberration of the cross section, and connecting the wavefront aberrations of the respective cross sections of the test object by moving at least one of the reference surface and the test object, thereby forming the wave front of the entire test object. It is decided to have a step of obtaining an aberration (claim 1).

(2). In (1), the reference surface is a flat surface, and a reflecting spherical surface is used as a means for reflecting the light that has passed through the object to be inspected. The test object was measured in a state where the center of curvature of the spherical surface and the focus position of the test object were substantially matched (claim 2).

(3). In (1), the reference surface is a spherical surface, and a reflection plane is used as a means for reflecting the light transmitted through the test object, and the test object is moved in the optical axis direction and a direction orthogonal to the optical axis direction. The object to be measured is measured in a state in which the focal point of the objective lens and the focal point of the lens to be inspected are substantially matched (claim 3).

(4). In (1), the reference surface is a flat surface, and a reflection plane is used as a means for reflecting the light transmitted through the test object. The reflection plane is moved in the optical axis direction along with the movement of the test object, The object to be measured is measured in a state in which the light collecting position by the object and the position of the reflection plane are substantially matched (claim 4).

(5). In (2) or (3) or (4), means for detecting the amount of movement of the reflecting spherical surface or the object or the reflecting plane in the optical axis direction when one-section interference fringes due to the wavefront aberration of the object occur. A means for storing the amount of movement in each cross section and a means for obtaining the locus of the image forming position of the test object formed at the position where the wavefront aberration of the test object is the minimum (claim 5).

(6). In (2), the means for detecting the amount of movement of the reflecting spherical surface in the optical axis direction when one-section interference fringes due to the wavefront aberration of the object are generated, and the respective amounts of movement associated with the movement of the reflecting spherical surface and the object to be inspected A means for storing is provided (Claim 6).

(7). In (3), a unit that detects the amount of movement of the object in the optical axis direction when one-section interference fringes due to the wavefront aberration of the object are generated, and the amount of movement is stored as the object moves. It has a means (Claim 7).

(8). In (4), the means for detecting the amount of movement of the reflecting plane in the optical axis direction when the one-section interference fringes due to the wavefront aberration of the subject are generated, and the amount of movement associated with each movement of the reflecting plane and the subject are described. It has a storage means (claim 8).

[0021]

Function: The transmitted light of the test object is used as the measurement information.

[0022]

【Example】

1. Examples corresponding to claims 2 and 6 (see FIGS. 1 and 2) In FIGS. 1 and 2, the light source 1 is a gas laser or a semiconductor laser having high coherence. The laser beam emitted from the light source 1 has its beam diameter expanded by the beam expander 2a and enters the spatial filter 3. The spatial filter 3 cuts off unnecessary light such as ghost light and reflected light.

The beam emitted from the spatial filter 3 is
The light enters the optical isolator 4 including the beam splitter 4a and the λ / 4 plate 4b. Further, the beam emitted from the optical isolator 4 has its beam diameter expanded by the beam expander 2b to be parallel light, and the reference plane plate 14 having a flat reference plane.
Leading to.

Even if a part of the beam incident on the reference plane plate 14 is reflected, it returns along the optical path. That is, after being deflected by the reflecting surface 4c of the beam splitter 4a, the condenser lens 9
After that, the image sensor 10 is reached.

On the other hand, the other part of the beam incident on the reference plane plate passes through the reference plane plate 14 and reaches the lens 5 to be inspected as an object to be inspected. The optical axis direction of this beam is the x-axis direction.
The test lens 5 having an anamorphic surface shape is mounted on the air slide table 13 which is movable in the y-axis direction, which is in a relationship orthogonal to the optical axis direction (x-axis direction), on the central axis OO.
(See FIG. 7) is aligned with the y-axis. The reference numeral 13a in FIG. 2 indicates the guide shaft of the air slide table 13.

The beam that has passed through the reference plane plate 14 passes through the lens 5 to be inspected, which is an object to be inspected, and is condensed at a condensing position behind the lens to be inspected by the condensing action of the lens to be inspected. , Becomes an expanded beam, and reaches the reflecting spherical surface 16a fixed on the table 17.

The table 17 is designed to be moved in the x-axis direction, and the linear encoder 18 detects the amount of movement. Moreover, the position resulting from the movement is the imaging position storage means 19
Stored by.

Here, the reflecting spherical surface 16a is a mirror having a center of curvature on the air slide table side, and has a condensing point at the center of curvature.

The beam reflected by the reflecting spherical surface 16a is returned to the original optical path, passes through the lens 5 to be inspected again, and has a wavefront aberration δ for one way in the xz section of the lens.
The image sensor 1 including the wavefront aberration of 2δ which is twice the
It reaches 0.

Here, when the focus position of the lens 5 to be inspected and the center of curvature of the reflecting spherical surface 16a are substantially matched, the returning light from the reference plane plate 14 and the returning light from the reflecting spherical surface 16a are superposed. Therefore, slit-shaped interference fringes are generated on the image sensor 10.

In this way, when the beam focusing position of the lens 5 to be inspected and the center of curvature of the reflecting spherical surface 16a are substantially aligned with each other, interference fringes are generated on the image sensor 10. Since this interference fringe includes wavefront aberration information in an arbitrary cross section of the lens to be inspected, it is proved to be a one-section interference fringe.

The occurrence of such interference fringes causes the lens 5 to be inspected.
It is determined that the image forming position is the image forming position, and the information from the image forming position storing means 19 is sent to the image forming position detecting device 20. Based on this information, the calculating device 21 analyzes it by using the Fourier transform method, and the information in the subject lens 5 Obtain information on wavefront aberration in a cross section.

This measurement result is only 1 of the lens 5 to be inspected.
It is only a cross section measurement. Therefore, in order to obtain information on the entire surface, a combination of movement of the air slide table 13 in the y-axis direction and movement of the base 17 in the x-axis direction is used in the x-z cross section of the lens 5 to be inspected in the y-axis direction. The measurement is sequentially performed, and these data are connected to obtain the wavefront aberration information of the entire lens 5 to be inspected.

That is, since the position of the converging point in the x-axis direction changes due to the movement of the air slide table 13 in the y-axis direction, the position of the reflecting spherical surface 16a is changed accordingly to match the center of curvature. Therefore, the movement of the table 17 is controlled. Further, the position at this time is detected by the linear encoder 18 and is stored in the image forming position storage means 19, whereby the locus of the image forming position when the lens 5 to be inspected is mounted on the scanning means can be known.

2. Examples corresponding to claims 3 and 7 (see FIGS. 3 and 4) As shown in FIGS. 3 and 4, in this example, regarding the arrangement of the optical members and the like closer to the light source 1 than the beam expander 2b, The arrangement is the same as that shown in FIGS. 1 and 2 according to the first example.

In this example, the beam emitted from the beam expander 2b is made incident on the objective lens 6 having a spherical reference surface 6a, and the objective lens 6 is arranged so that it can be finely adjusted in the axial direction. .

Therefore, even if a part of the beam is reflected by the reference surface 6a of the objective lens 6, the beam returns through the optical path and the other part of the beam is transmitted, and the transmitted light is condensed by the objective lens 6. After being condensed by the action at the condensing position, it becomes a diverging spherical wave and is incident on the lens 5 to be inspected.

The incident light passes through the lens 5 to be inspected and is incident on the reflection plane 16b. This reflection plane 16b is fixed to a stationary member. Here, the lens 5 to be inspected has a central axis OO in the y-axis direction with the G main diameter line side facing the reflection plane 16b side.
(See FIG. 7) and are mounted on the base 17.

The base 17 is provided on an air slide table 13 which is movable in the y-axis direction, and the base 17 is movable on the air slide table in the x-axis direction orthogonal to the y-axis direction. The moving amount is detected by the linear encoder 18. Therefore, the lens 5 to be inspected is movable in the x-axis and y-axis directions.

By moving the lens 5 to be tested in the xy directions by the air slide table 13 and the table 17, the converging point of the objective lens 6 and the focal position of the lens 5 to be tested can be matched. This matching position is indicated by the symbol P in FIGS. 3 and 4.
In such a matched state, interference fringes are generated on the image sensor 10. Thereby, x-z in the lens 5 to be inspected
Information on the wavefront aberration at the cross section can be obtained.

Next, since the position of the focal point in the x-axis direction is changed by the movement of the air slide table 13 in the y-axis direction, the position of the lens 5 to be inspected in the x-axis direction is changed by moving the table 17. Adjustment is performed to obtain coincidence of both condensing positions, and wavefront aberration information at each cross-sectional position of the lens under test is obtained.

These positions are detected by the linear encoder according to the above-mentioned example 1 and stored in the image forming position storage means, and the locus of the image forming position when the lens 5 to be inspected is mounted on the scanning means is known. be able to.

3. Examples corresponding to claims 4 and 8 (see FIGS. 5 and 6) As shown in FIGS. 5 and 6, in this example, regarding the arrangement of each optical member and the like closer to the light source 1 than the beam expander 2b, The arrangement is the same as that shown in FIGS. 1 and 2 according to the first example.

In this example, the outgoing beam from the beam expander 2b is made incident on the reference plane plate 14 having a plane reference plane. The plane reference plate 14 is fixedly provided on the immovable member.

A part of the incident beam is reflected by the reference plane plate 14 and returns to the original optical path. The other part of the incident beam passes through the flat reflecting plate 14 and enters the lens 5 to be inspected as parallel light. This incident light passes through the lens 5 to be inspected and is incident on the reflection plane 16b. The reflecting plane 16b is mounted on a table 17 and is movable together with the table 17 in the same x-axis direction as the optical axis direction.

Here, the lens 5 to be inspected is movable in the y-axis direction by aligning the central axis OO (see FIG. 7) in the y-axis direction with the G main diameter line side facing the reference plane plate 14 side. It is mounted on the slide table 13.

When the reflection plane 16b is located on the condensing point of the beam transmitted through the lens 5 to be inspected, a so-called cat's eye state occurs, and the return light thereof is superposed on the return light from the reference plane plate 14. An interference fringe is generated on the image sensor 10 as in the above-described examples.

In the following, the slide table 13 and the table 17 are moved according to the above example to obtain the wavefront aberration information in each cross section of the lens to be inspected, and the wavefront aberration information of the entire lens to be inspected 5 is obtained.

[0049]

According to the present invention, it is possible to obtain the wavefront aberration information in consideration of the internal information of the object to be inspected.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an optical system illustrating a first embodiment of the present invention when viewed from the front.

FIG. 2 is an explanatory view of the optical system for explaining the first embodiment of the present invention when viewed from the side.

FIG. 3 is an explanatory view of an optical system for explaining a second embodiment of the present invention when viewed from the front.

FIG. 4 is an explanatory view of the optical system for explaining the second embodiment of the present invention when viewed from the side.

FIG. 5 is an explanatory diagram of an optical system for explaining a third embodiment of the present invention when viewed from the front.

FIG. 6 is an explanatory view of the optical system for explaining the third embodiment of the present invention when viewed from the side.

FIG. 7 is an explanatory diagram of a test lens having an anamorphic shape.

[Explanation of symbols]

 5 Lens to be inspected (as an object to be inspected) 6a Reference surface 13 Air slide table 14 Reference flat plate 16a Reflective spherical surface 16b Reflective flat surface 17 units

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[Procedure amendment]

[Submission date] September 14, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

[0010]

[Problems to be Solved by the Invention]
The TL measuring device is intended to measure the surface accuracy of a flat surface , a cylinder surface, a barrel toroidal surface, or the like, which is an object to be inspected. Internal information of the object to be inspected, for example, bubbles inside the object or striae. It is not possible to obtain measurement information including nonuniformity in a transparent medium such as.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction content]

In this example, the outgoing beam from the beam expander 2b is made incident on the objective lens 6 having the spherical reference surface 6a, and the objective lens 6 is arranged so that it can be finely adjusted in the x-axis direction. ing.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0045

[Correction method] Change

[Correction content]

A part of the incident beam is reflected by the reference plane plate 14 and returns to the original optical path. The other part of the incident beam passes through the reference reflection plate 14 and enters the lens 5 to be inspected as parallel light. This incident light passes through the lens 5 to be inspected and is incident on the reflection plane 16b. The reflecting plane 16b is mounted on a table 17 and is movable together with the table 17 in the same x-axis direction as the optical axis direction.

Claims (8)

[Claims] 1. A method for measuring the accuracy of an object to be measured by irradiating an object to be measured and a reference surface serving as a reference with coherent light from the same light source and superimposing return light from these to form interference fringes. A step of irradiating the reference surface and the test object with coherent light from a light source and superimposing the reflected light from the reference surface and the light transmitted through the test object to generate one-section interference fringes; The step of analyzing the cross-sectional interference fringes to obtain the wavefront aberration of the cross section, and connecting the wavefront aberration of each cross section of the test object by moving at least one of the reference surface and the test object The method for measuring the wavefront aberration of an object having an anamorphic shape, comprising: 2. The reference surface according to claim 1, wherein the reference surface is a flat surface,
A reflecting spherical surface is used as a means for reflecting the light transmitted through the test object, and the reflecting spherical surface is moved in the optical axis direction along with the movement of the test object so that the center of curvature of the reflecting spherical surface and the light collection by the test object. A method for measuring a wavefront aberration of an object having an anamorphic shape, which is characterized in that the object is measured in a state where the positions are substantially matched. 3. The reference surface according to claim 1, wherein the reference surface is a spherical surface,
A reflection plane is used as a means for reflecting the light transmitted through the test object, and the test object is moved in the optical axis direction and in a direction orthogonal to the optical axis direction. A method of measuring a wavefront aberration of an object having an anamorphic shape, which comprises measuring the object in a state where focal points are substantially matched. 4. The reference surface according to claim 1, wherein the reference surface is a plane,
A reflection plane is used as a means for reflecting the light transmitted through the test object, and the reflection plane is moved in the optical axis direction along with the movement of the test object, so that the light collecting position by the test object and the position of the reflection plane. A method of measuring a wavefront aberration of an object having an anamorphic shape, comprising: 5. The movement amount in the optical axis direction of the reflecting spherical surface or the object or the reflecting plane when one-section interference fringes are generated by the wavefront aberration of the object according to claim 2, 3, or 4. Anamorphic, characterized by having means for detecting the distance, means for storing the amount of movement in each cross section, and means for obtaining the locus of the imaging position of the test object with the position where the wavefront aberration of the test object is the minimum. Device for measuring wavefront aberration of an object having a unique shape. 6. The means for detecting the amount of movement of the reflecting spherical surface in the optical axis direction when one-section interference fringes are generated due to the wavefront aberration of the measuring object, and the moving of the reflecting spherical surface and the object according to claim 2. A wavefront aberration measuring apparatus for an object having an anamorphic shape, characterized by having a means for storing each movement amount involved. 7. The means for detecting the amount of movement of the test object in the optical axis direction when one-section interference fringes are generated due to the wavefront aberration of the test object according to claim 3, and A wavefront aberration measuring apparatus for an object having an anamorphic shape, characterized by having a means for storing a movement amount. 8. The means for detecting the amount of movement of the reflecting plane in the optical axis direction when one-section interference fringes due to the wavefront aberration of the subject are generated, and the moving of the reflecting plane and the subject according to claim 4. A wavefront aberration measuring apparatus for an object having an anamorphic shape, characterized by having a means for storing each movement amount involved.