JP2002188979A - Measuring method of refractive index distribution and measuring device of refractive index distribution, and manufacturing method of optical system and optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure accurately a primary component (inclination component) of a refractive index distribution of a test object. SOLUTION: A measuring device for measuring the wave front shape of light transmitted through the test object is used, and the attitude of the test object is changed to a position determined by being rotated around the optical axis of the measuring device as much as a prescribed angle, and first measurement data and second measurement data outputted respectively before and after the change by the measuring device are acquired, and the difference between the first measurement data and the second measurement data is determined as information for showing the primary component (inclination component) of the refractive index distribution of the test object. The primary component (inclination component) of the refractive index distribution follows the attitude change, but a primary error component generated in the measuring device does not follow it. Therefore, the primary component (inclination component) of the refractive index distribution appears in the difference between the two measurement data, but the primary error component in the measuring device does not appear therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of measuring a refractive index distribution for obtaining a refractive index distribution of an object using a measuring instrument such as an interferometer, a measuring apparatus of a refractive index distribution, and an optical system. The present invention relates to a manufacturing method and an optical system.

[0002]

2. Description of the Related Art In examining the refractive index distribution of an optical member such as glass, the shape of the wavefront of transmitted light (hereinafter referred to as "transmitted wavefront") of a test object is measured by a measuring instrument such as an interferometer. . This is because the shape of the transmitted wavefront depends on the refractive index distribution of the test object. For example, in the Fizeau interferometer shown in FIG. 19, a test object 1910a is arranged between a Fizeau member 191 and a folding mirror 192, and a light source 19
The light (reference light) reflected from the Fizeau surface 191a after being emitted from the light source 193 and the Fizeau member 191 and the test object 1910a transmitted in this order after being emitted from the light source 193 and reflected by the reflection surface 192a of the return mirror 192. The light (measurement light) reflected and transmitted again through the test object 1910a and the Fizeau member 191 in this order interferes with each other, and an interference fringe generated thereby causes a two-dimensional image sensor (image sensor) 194
Etc. are detected.

However, in order to measure the refractive index distribution, the test object 1910a is to be measured so that the surface accuracy error of the test object 1910a does not affect the pattern of occurrence of interference fringes. It is loosely inserted between two reference glasses 1910b having the same refractive index as the average refractive index and having the surfaces polished with sufficient precision. The subject 1
The gap between 910a and each reference glass 1910b is filled with an oil having a refractive index substantially equal to the average refractive index thereof (hereinafter, the test object 1910a and the reference glass 1910b).
The system consisting of b and oil is referred to as a "measurement cell". Reference numeral 1910 in the figure).

The detected interference fringes are converted to phase distribution data Ψ (X, Y) (which is a phase difference distribution between the reference light and the measurement light).
Is converted into data of the transmitted wavefront of the measurement cell 1910. Hereinafter, the coordinates (X, Y) are defined as XY coordinates in a rectangular coordinate system in which the Z axis is made coincident with the optical axis.

Further, the same measurement is performed on the measuring cell 1910 that does not include the test object 1910a to obtain phase distribution data Ψ ′ (X, Y), and the phase distribution data Ψ ′ (X, Y) By calculating the difference (difference) between the phase distribution data and the phase distribution data Ψ (X, Y), phase distribution data including only information on the refractive index distribution of the test object 1910a can be obtained.

[0006] From this phase distribution, the refractive index distribution data Φ (X, Y) of the test object 10a can be obtained. The conversion from the phase to the refractive index can be performed only by multiplying a constant according to the thickness d of the test object and the light source wavelength λ. By the way, in the refractive index distribution data Φ (X, Y) obtained from the difference (difference) between the two measurements, the error components relating to the measuring instrument and the two reference glasses 1910b should be eliminated. is there.

Therefore, conventionally, in the field of manufacturing optical systems, the refractive index distribution of an optical member to be used could be examined with sufficiently high accuracy by the above-described measuring method. Incidentally, in the field of manufacturing optical systems, the refractive index distribution data Φ (X, Y) is subjected to function fitting, and its second-order component Φ ₂ (X, Y), third-order component Φ ₃ (X, Y), In many cases, the next components Φ ₄ (X, Y),...

[0008]

However, the refractive index distribution data Φ (X, Y) also includes the inclination angle of the folding mirror 192 with respect to the optical axis of the interferometer (see FIG. 19),
An error due to poor parallelism between the two reference glasses 1910b remains superimposed. And these errors, the primary component _{(T x X + T y Y} ) represented by the type of error (hereinafter, referred to. "Primary error component").

Therefore, if the refractive index distribution data Φ
(X, Y) or the first-order component from [Phi ₁ (X, Y) be extracted, its value is the first order error component due to the poor parallelism of the inclination angle and the reference glass 1910b mirrors 192 However, it cannot be distinguished from the primary component (gradient component) of the refractive index distribution of the test object 1910a. As described above, in the conventional optical system manufacturing field, there was no problem because the evaluation target was the second and subsequent components of the refractive index distribution data, but there was no problem. In the field of manufacturing optical systems that require
In the future, a primary component (gradient component) may be added to the evaluation target in order to grasp the characteristics more accurately.

Accordingly, the present invention provides a method of measuring a refractive index distribution and a measuring apparatus of a refractive index distribution capable of accurately measuring a primary component (gradient component) of a refractive index distribution of a test object, and a high-performance device. It is an object of the present invention to provide an optical system manufacturing method and an optical system. In this specification, in order to distinguish the primary component of the refractive index distribution data, which is the measurement data, from the primary component of the actual refractive index distribution, the latter primary component is referred to as “tilt component”. Call it.

[0011]

A method for measuring a refractive index distribution according to any one of claims 1 to 9, wherein the refractive index distribution is measured using a measuring device for measuring a wavefront shape of light transmitted through a test object. A method of measuring the rate distribution, wherein the posture of the test object in the measuring instrument is changed to a position rotated by a predetermined angle around the optical axis of the measuring instrument, and the measuring instrument is changed before and after the change. The first measurement data and the second measurement data to be output are acquired, and the difference between the first measurement data and the second measurement data is determined by using the primary component (gradient) of the refractive index distribution of the test object. Component).

Although the primary component (inclined component) of the refractive index distribution follows this change of the attitude, the primary error component generated in the measuring instrument does not follow. Therefore, the primary component (gradient component) of the refractive index distribution appears in the difference between the two measurement data, and the primary error component in the measuring instrument does not appear. Further, in the method for measuring a refractive index distribution according to any one of claims 2 to 9,
The predetermined angle is set to 180 °.

Further, in the method for measuring a refractive index distribution according to any one of claims 3 to 5 to 9,
The difference between the measured data of the second and the second measured data,
A primary component of the obtained difference is extracted as information indicating a primary component (gradient component) of the refractive index distribution of the test object. In the method for measuring a refractive index distribution according to any one of claims 4 to 9, the primary component of the first measurement data and the primary component of the second measurement data are respectively set. The difference between the extracted primary components is determined as information indicating the primary component (gradient component) of the refractive index distribution of the test object.

Among them, the operation of extracting the primary component from the measurement data can be easily executed using existing software. In the method for measuring a refractive index distribution according to any one of claims 5 to 9, the measuring device may include a measuring light transmitted through the test object and a reference light having a predetermined wavefront shape. An interference optical system for causing interference and detecting an interference fringe generated by the interference as information indicating a wavefront shape of the measurement light, and an inclination angle of an optical axis of the measurement light and / or an inclination angle of an optical axis of the reference light. Using an interferometer having an optical axis tilting mechanism for changing, when the attitude is changed, by driving the optical axis tilting mechanism, the interference fringes generated before and after the change, respectively. The density is kept coarse enough to be detectable, and in accordance with the amount of change given to the tilt angle of the optical axis by driving the optical axis tilt mechanism, a correction operation is performed on the process of obtaining the information or the obtained result. Apply.

In the method of measuring a refractive index distribution according to any one of claims 6, 8 and 9, the measuring arm of the interference optical system and / or the reference may be used as the optical axis tilting mechanism. Use a wedge plate inserted into the arm. In the method for measuring a refractive index distribution according to any one of claims 7 to 9, the optical axis tilting mechanism includes a reflecting surface that deflects measurement light and / or reference light of the interference optical system, And a mechanism for inclining the reflection surface.

This reflecting surface is provided in advance in an interference optical system in the measuring instrument. Therefore, the optical axis tilting mechanism utilizes the reflection surface in the interference optical system for changing the tilt angle of the optical axis. In the method of measuring a refractive index distribution according to claim 8 or 9, the test object is provided between two reference glasses via a liquid.

According to a ninth aspect of the present invention, the refractive index of the reference glass and the refractive index of the liquid are substantially the same as the average refractive index of the test object. Further, the apparatus for measuring a refractive index distribution according to any one of claims 10 to 18 drives and controls a measuring device for measuring a wavefront shape of transmitted light of a test object and each unit of the measuring device. A measurement device for a refractive index distribution, comprising: a control unit, and a calculation unit that performs a calculation on measurement data output by the measurement device, wherein the measurement device determines a posture of the test object by using the measurement device. Has a posture changing mechanism that changes to a state rotated by a predetermined angle around the optical axis, the control unit changes the posture of the test object by driving the posture changing mechanism, and changes the posture of the test object. In each of before and after, the first measurement data and the second measurement data output by the measuring device are obtained, and the calculation unit
A difference between the first measurement data and the second measurement data is obtained as information indicating a first-order component (gradient component) of the refractive index distribution of the test object.

Further, in the apparatus for measuring a refractive index distribution according to any one of claims 11 to 18, the predetermined angle is set to 180 °. In the apparatus for measuring a refractive index distribution according to any one of claims 12 to 14, the arithmetic unit may calculate a difference between the first measurement data and the second measurement data. And a primary component of the obtained difference is extracted as information indicating a primary component (gradient component) of the refractive index distribution of the test object.

Further, any one of claims 13 to 18
In the refractive index distribution measuring device according to the paragraph, the arithmetic unit,
A primary component of the first measurement data and a primary component of the second measurement data are respectively extracted, and a difference between the extracted primary components is calculated as a primary component of a refractive index distribution of the test object. It is obtained as information indicating a component (gradient component). Claim 1
In the apparatus for measuring a refractive index distribution according to any one of claims 4 to 18, the measuring device causes the measurement light transmitted through the test object and the reference light having a predetermined wavefront shape to interfere with each other,
An interference optical system that detects interference fringes generated by the interference as information indicating the wavefront shape of the measurement light, and an optical axis that changes the inclination angle of the optical axis of the measurement light and / or the inclination angle of the optical axis of the reference light A tilting mechanism, and a detecting unit that detects a change amount of the tilt angle generated in the optical axis by driving the optical axis tilting mechanism, wherein the control unit controls the optical axis tilting mechanism when changing the posture. By driving, each of the fringe densities of the interference fringes before and after the change is maintained at a predetermined value or less, and the calculation unit obtains the information according to the amount of change detected by the detection unit. Alternatively, a correction operation is performed on the obtained result.

Further, claim 15, claim 17, and claim 1
9. In the refractive index distribution measuring device according to any one of the items 8, the optical axis tilting mechanism includes a wedge plate inserted into a measuring arm and / or a reference arm of the interference optical system. Moreover, in the refractive index distribution measuring device according to any one of claims 16 to 18, the optical axis tilting mechanism includes a reflecting surface that deflects the measuring light and / or the reference light of the interference optical system. And a mechanism for inclining the reflection surface.

In the apparatus for measuring a refractive index distribution according to claim 17 or 18, the test object is provided between two reference glasses via a liquid. In the refractive index distribution measuring device according to the eighteenth aspect, the refractive index of the reference glass and the refractive index of the liquid are substantially the same as the average refractive index of the test object. These measuring apparatuses for refractive index distribution according to claims 10 to 18 automatically perform the measuring method for refractive index distribution according to claims 1 to 9, respectively.

In the method for manufacturing an optical system according to the nineteenth aspect, the first-order component (gradient component) of the refractive index distribution of the optical member constituting the optical system is defined by any one of the first to ninth aspects. The optical system is measured or measured by the method for measuring the refractive index distribution described above, and the optical system is adjusted or processed in accordance with the primary component (gradient component) of the measured refractive index distribution. In the optical system according to the twentieth aspect, the primary component (gradient component) of the refractive index distribution is obtained by the method for measuring the refractive index distribution according to any one of the first to ninth aspects.
Is provided with an optical member measured in advance, and the optical member has a shape and / or an arrangement corresponding to a primary component (inclined component).

According to the nineteenth and twentieth aspects, it is possible to suppress the adverse effect of the primary component (gradient component) of the refractive index distribution of the optical member on the imaging performance of the optical system.

[0024]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] First, a first embodiment of the present invention will be described with reference to FIGS. 1, 2, 3 and 4. In the present embodiment, a gradient component of the refractive index distribution is calculated. Therefore, hereinafter, the configuration and operation necessary for calculating the tilt component will be mainly described.

(Configuration) FIG. 1 is a view for explaining a refractive index distribution measuring system 1 of the present embodiment. In FIG. 1,
The same components as those in FIG. 19 are denoted by the same reference numerals. The refractive index distribution measurement system 1 includes an interference measurement device 10 including various optical systems and their driving mechanisms and driving circuits.
And an information processing device 18 such as a computer.

The interference measuring apparatus 10 has an interference optical system similar to the conventional one, that is, a light source 193 and a light beam diameter conversion optical system 19.
6, a beam splitter 195, a Fizeau member 191, a folding mirror 192, an observation optical system 197, and an image sensor 194. The measurement cell 15 having the test object 15 a whose refractive index distribution is to be measured is inserted between the folding mirror 192 and the Fizeau member 191.

As shown in FIG. 2, the measuring cell 15 has two reference glasses 15b, and a test object 15a is loosely inserted between the reference glasses 15b. Reference glass 15b
Has the same refractive index as the average refractive index of the test object 15a, and its surface is polished in advance so that the surface accuracy error is sufficiently small. The material of the reference glass 15b is preferably the same glass material as the test object 15a.

The test object 15a and each reference glass 15b
Is filled with oil having a refractive index substantially equal to the average refractive index. It should be noted that other liquids may be used as long as the refractive index is the same as that of the test object 15a, not oil. Furthermore, the test object 1 in the measurement cell 15 of the present embodiment
5 a is configured to be rotatable at least 180 ° around the optical axis of the interference measurement device 10 by the rotation mechanism 14. However, during this rotation, the two reference glasses 15b are fixed to the interference measurement device 10 side.

For example, the rotating mechanism 14 includes a holder that supports the test object 15a from the periphery thereof and that can rotate around the optical axis, a motor that applies a rotating force to the holder, and the like. Note that a part or all of the rotating mechanism 14 may be attached to the measurement cell 15 side or may be attached to the interference measurement device 10 side. By supporting the test object 15a with this holder, the rotation axis of the test object 15a can be made to coincide with the optical axis with high accuracy.

Here, in the operation of the control unit 11 to be described later, since the angle at which the test object 15a is to be rotated is determined to be a predetermined angle (180 °), the rotation angle of the holder is limited to a predetermined angle. To provide a stopper, or use a motor such as a stepping motor that can control the rotation angle of the holder to a predetermined angle according to the value of the drive signal, or use a DC motor and detect the rotation angle of the holder It is preferable to provide a sensor that performs the measurement.

Further, the interference measuring apparatus 10 includes a moving mechanism 12 for moving the Fizeau surface 191a in the optical axis direction (fringe scan), a tilting mechanism 13 for tilting the folding mirror 192, and a control unit 11 for driving each unit. Be provided. The rotating mechanism 14 is also driven by the control unit 11. The tilting mechanism 13 of the folding mirror 192
In the case where the fringe density of the interference fringes becomes extremely high and it becomes difficult to perform detection by the image sensor 194 or to convert the interference fringes into phase distribution data (described later), the inclination angle of the optical axis is measured before measurement. It is commonly used to adjust.

However, the present embodiment is applied when the gradient component of the refractive index distribution of the test object 15a falls within a predetermined range and the fringe density of the interference fringes becomes sufficiently coarse. The tilt mechanism 13 is not essential.

According to the configuration described above, the light emitted from the light source 193 is converted into a parallel light beam having an appropriate diameter by the light beam diameter conversion optical system 196, and is transmitted to the Fizeau member 191 via the beam splitter 195. After entering, a part of the light is reflected on the Fizeau surface 191a and becomes reference light.
On the other hand, some other light passes through the Fizeau member 191 and
After passing through the measurement cell 15, the light is reflected by the reflection surface 192a of the return mirror 192, and again passes through the measurement cell 15 and the Fizeau member 191 to become measurement light.

The reference light and the measurement light are deflected in the direction of the observation optical system 197 via the beam splitter 195, and then cause interference fringes on the image sensor 194. The information processing device 18 is an information processing device such as a computer having a CPU, a memory, a hard disk, and the like (not shown). The processing executed by the CPU includes a phase distribution calculating unit 18a, a refractive index distribution Calculation unit 18
b.

Some or all of the processing in the information processing device 18 is executed by software, but is also executed by hardware (such as a board dedicated to the interference measurement device 10 mounted on the information processing device 18). You may. Further, the processing in the information processing device 18 may be distributed and executed by a plurality of information processing devices.

The processing of the control unit 11 in the interference measuring apparatus 10, the phase distribution calculating unit 18a, and the refractive index distribution calculating unit 1
Part or all of 8b may be executed on the interference measurement device 10 side or the information processing device 18 side. Further, in the interference measurement apparatus 10, a simple beam splitter 195 is used as an optical system for splitting a light beam in two directions. However, a polarization beam beam generally used to suppress a decrease in the amounts of measurement light and reference light is used. It may be a splitter. However, in this case, a 波長 wavelength plate is inserted between the Fizeau member 191 and the polarizing beam splitter.

As for the correspondence between the configuration described above and the claims, the interferometer 10 and the phase distribution calculator 18a correspond to a measuring device and a controller, and the refractive index distribution calculator 18b corresponds to an arithmetic unit. Correspondingly, the rotation mechanism 14 corresponds to the attitude changing mechanism. (Operation) FIG. 3 is an operation flowchart of the refractive index distribution measurement system 1 of the present embodiment. FIG. 4 is a diagram illustrating the operation of the present embodiment.

Steps S1 to S3 are processing by the control unit 11, step S4 is processing by the phase distribution calculating unit 18a, and steps S5 to S7 are processing by the refractive index distribution calculating unit 18b. In the present embodiment, prior to the measurement of the refractive index distribution, the reflection surface 19 of the folding mirror 192 is used.
2a is adjusted substantially perpendicular to the optical axis, and it is assumed that the tilt angle of the return mirror 192 is kept the same at least at the time of interference measurement in the following steps S1 and S3.

First, the control section 11 drives each section of the interference measuring apparatus 10 based on a predetermined interference measurement method to perform interference measurement and obtain interference fringe data (step S1). The predetermined interference measurement method is, for example, a fringe scan method to which the 5-bucket method is applied. In the fringe scan method to which the five bucket method is applied, the light source 193 is driven to generate interference fringes on the image sensor 194, and the moving mechanism 12 is driven to move the Fizeau member 191 a predetermined distance in the optical axis direction (the light source 193). (Fringe scan) while continuously or intermittently reciprocating at a predetermined speed by a distance corresponding to the wavelength of light (fringe scan), while continuously interfering fringe data (distribution of light accumulation amount) accumulated by the image sensor 194 per unit time. And take it five times.

Next, the controller 11 drives the rotating mechanism 14 to rotate the test object 15a in the measuring cell 15 by 180 ° around the optical axis (step S2). In this state, the control unit 11 performs the same interference measurement as in step S1, and acquires interference fringe data (step S3).

The interference fringe data obtained in steps S1 and S3 is taken into the information processing device 18. Next, the phase distribution calculation unit 18a in the information processing device 18 converts the interference fringe data acquired in step S1 into phase distribution data, and
3. Convert the interference fringe data acquired in step 3 into phase distribution data.

Hereinafter, the former phase distribution data is expressed as
_Before (X, Y) and the latter phase distribution data
_After (X, Y) (step S4, FIG. 4
(A)). The conversion from the interference fringe data to the phase distribution uses a well-known conversion formula based on the predetermined interference measurement method. Here, the phase distribution data Ψ _Before (X, Y) and Ψ _After (X, Y) obtained in step S4 are represented by the following equations (1) and (2), respectively.

Ψ _Before (X, Y) = Ψ _Sta (X, Y) + ir _Mir (X, Y) + Ψ _Tes (X, Y)-Ψ _ref (X, Y) ... (1) Ψ _After (X , Y) = Ψ _Sta (X, Y) + Ψ _Mir (X, Y) + Ψ _Tes (-X, -Y)-Ψ _ref (X, Y) ... (2) where Ψ _Sta (X, Y) Is the wavefront change that occurs when the light passes through the two reference glasses 15b twice, Ψ _Mir (X, Y)
Is the wavefront change that occurs when the light is reflected by the reflection surface 192a of the return mirror 192, Ψ _Tes (X, Y) is the wavefront change that occurs when the light passes through the test object 15a twice, Ψ
_ref (X, Y) is a wavefront change generated when the light is reflected by the Fizeau surface 191a.

Next, the refractive index distribution calculating section 18b calculates the gradient component of the refractive index distribution by using these two phase distribution data Ψ to eliminate extra information.
_Before (X, Y), Ψ Difference of _After (X, Y) Ψ (X, Y)
Y) is obtained (step S5, FIG. 4B).

According to the above equations (1) and (2), the difference Ψ
(X, Y) is represented by the following equation (3). Ψ (X, Y) = Ψ After (X, Y) -Ψ Before (X, Y) = Ψ Tes (-X, -Y) -Ψ Tes (X, Y) ... (3) that is, the difference calculation According to the extra information (Ψ _Sta (X,
Y), Ψ _Mir (X, Y), Ψ _Tes (X, Y), Ψ
_ref (X, Y)) is erased. These erased information includes a first-order error component which could not be separated from the gradient component of the refractive index distribution conventionally.

Further, this difference calculation is based on the phase distribution data Ψ
Of the components of _Before (X, Y) and Ψ _After (X, Y), the components of the pattern that do not change even when rotated 180 ° around the optical axis of the interference measurement apparatus 10 are also deleted. As shown in FIG. 4B, components other than the first-order component (gradient component) of the refractive index distribution of the test object 15a have a difference Ψ.
It is not included in (X, Y).

That is, according to this angle setting, the primary component (inclined component) of the refractive index distribution can be easily obtained from the difference (difference). Then, in the difference obtained as a result of the angle setting and the difference calculation, the primary error component is reliably removed, and the primary component (tilt component) of the refractive index distribution is securely left. Therefore, this difference Ψ
(X, Y) can be regarded as indicating a gradient component of the refractive index distribution.

The difference Ψ (X, Y) is a discrete data because it is a difference between measured data.
Therefore, for this difference Ψ (X, Y), the function N
_{(X, Y) = T x} X + T y , etc. may the performed function fitting to Y. Then, conversion from the phase to the refractive index (multiplication of a constant according to the thickness d of the test object 15a and the light source wavelength λ) and normalization (multiplication of a constant according to a method of obtaining the difference)
By performing such processing, a gradient component can be obtained.

However, due to the deviation between the rotation axis in step S2 and the optical axis of the interference measuring device 10, the poor reproducibility of the measurement in steps S1 and S3 (the reproducibility of the moving pattern of the fringe scan), etc. There is a possibility that a slight error represented by the next component is superimposed on the difference Ψ (X, Y). Therefore, in order to make the calculation of the gradient component of the refractive index distribution highly accurate, in the present embodiment, the difference Ψ (X, Y)
From the primary component Ψ ₁ (X, Y).

That is, in the subsequent step S6, the refractive index distribution calculating unit 18b adds the function N ′ (X,
Y) = use a _{T x X + T y Y +} A. Then, using the values of the coefficients T _x and T _y obtained by the least square method or the like, the difference Ψ
The primary component Ψ ₁ (X, Y) of (X, Y) is represented by the following equation (4) (FIG. 4C).

Ψ ₁ (X, Y) = T _x X + T _y Y (4) Further, the obtained primary component Ψ ₁ (X, Y) is converted from a phase into a refractive index and normalized. By performing such a process, the gradient component Φ ₁ (X, Y) of the refractive index distribution of the test object 15a can be obtained as in the following equation (5) (step S7,
FIG. 4D). Φ ₁ (X, Y) = T _x 'X + T _y ' Y (5) As described above, in the present embodiment, steps S1,
By the two measurements in S3 and the difference calculation (step S5), unnecessary information (first-order error component) is reliably removed while leaving necessary information (gradient component of the refractive index distribution). The gradient component of the refractive index distribution 15a is determined with high accuracy.

[Second Embodiment] Next, a second embodiment of the present invention will be described with reference to FIGS. Here, only the differences from the first embodiment will be described, and the description of the other parts will be omitted.

(Configuration) FIG. 5 is a view for explaining the refractive index distribution measuring system 2 of the present embodiment. The refractive index distribution measurement system 2 is the same as the refractive index distribution measurement system 1 except that the information processing device 28 is provided instead of the information processing device 18. The information processing device 28 is an information processing device such as a computer provided with a CPU, a memory, a hard disk, and the like (not shown), like the information processing device 18.

However, the processing executed by the CPU of the information processing apparatus 28 is the same as the processing executed by the CPU of the information processing apparatus 18 except that the refractive index distribution calculating section 28b is inserted instead of the refractive index distribution calculating section 18b. equal. (Operation) FIG. 6 is an operation flowchart of the refractive index distribution measurement system 2 of the present embodiment.

In FIG. 6, steps that are the same as the steps shown in FIG. 3 are given the same reference numerals, and descriptions thereof will be omitted. Steps S1 to S3 in FIG. 6 are processing by the control unit 11, step S4 is processing by the phase distribution calculation unit 18a, and steps S25, S26, and S27.
Is a process by the refractive index distribution calculation unit 28b. The refractive index distribution calculation unit 28b of the present embodiment calculates the phase distribution data Ψ obtained in steps S1 to S4.
_{From each of Before} (X, Y) and Ψ _After (X, Y), the primary components Ψ1 _Before (X, Y), Ψ1 _After (X, Y)
Y) are extracted (step S25).

Incidentally, this extraction is based on the phase distribution data Ψ
_{For each of Before} (X, Y) and Ψ _After (X, Y), the function fitting to a polynomial function consisting of terms of each order such as 0th, 1st, 2nd, 3rd,. Is to be applied. Hereinafter, each of the obtained primary components is represented by Ψ
1 _Before (X, Y) and Ψ1 _After (X, Y). Here, from the operation of converting the interference fringe data into the phase distribution data (step S4), the phase distribution data Ψ (X, Y) is function-fitted to a polynomial function (step S2).
The calculation up to 5) is a well-known calculation applied to the conventional method of measuring the refractive index distribution, and software for executing the calculation is also existing.

Therefore, existing software can be used for these steps. Next, the refractive index distribution calculation unit 28b calculates the extracted primary component Ψ1
_Before (X, Y), Ψ1 Difference between _After (X, Y) Ψ ₁
(X, Y) is obtained (step S26). Further, if the difference Ψ ₁ (X, Y) is subjected to processing such as conversion from phase to refractive index and normalization as in step S7 of FIG. 3, the gradient of the refractive index distribution of the test object 15a is obtained. The component Φ ₁ (X,
Y) can be obtained (step S27).

As described above, in the present embodiment, the procedure of extracting the primary component (step S25) is executed before the procedure of the difference calculation (step S26), so that existing software can be used. However, since the object of the function fitting in the extraction procedure (step S25) is the data before the extra information is removed, the extraction accuracy is slightly reduced, and the finally obtained gradient component Φ of the refractive index distribution is obtained. ₁ The calculation accuracy of (X, Y) is slightly reduced as compared with the first embodiment.

That is, the present embodiment is a refractive index distribution measuring system for inexpensively measuring the gradient component of the refractive index distribution of the test object 15a. [Third Embodiment] Next, a third embodiment of the present invention will be described with reference to FIGS. 7, 8, 9, and 10. FIG.

Here, only the differences from the first embodiment will be described, and the description of the other parts will be omitted. (Configuration) FIG. 7 is a view for explaining the refractive index distribution measurement system 3 of the present embodiment.

The refractive index distribution measuring system 3 includes an interference measuring device 30 and an information processing device 38. The interference measuring device 30 is different from the interference measuring device 10 of the first embodiment in that two wedge plates 35a and 35b for adjusting the tilt angle of the optical axis are provided between the measuring cell 15 and the folding mirror 192. The optical axis tilting cell 35 (see FIG. 8) is inserted and these wedge plates 35a, 35b are inserted.
Are equivalent to those provided with rotation mechanisms 36a and 36b for respectively rotating and the control unit 31 instead of the control unit 11. The rotation mechanisms 36a and 36b are driven by the control unit 31.

As shown in FIG. 8, when the wedge plates 35a and 35b in the optical axis tilting cell 35 are respectively rotated around the optical axis, the light emission angle from the wedge plate 35a and the wedge The emission angle of light from the plate 35b is
Each changes. Utilizing this principle, the optical axis tilting cell 35 is configured such that the optical axis tilt angle (TL _X , It has a function of freely changing the TL _y).

The optical axis tilting cell 35 and its rotating mechanisms 36a and 36b are common to the folding mirror 192 and the tilting mechanism 13 in that the tilt angle of the optical axis can be adjusted. Note that the rotation mechanism 36a includes a wedge plate 35a.
Is supported by the periphery thereof, and is configured by a holder rotatable around the optical axis of the interference measurement device 30, a motor that applies a rotational force to the holder, and the like.
The wedge plate 35b is supported by a peripheral edge thereof, and is configured by a holder rotatable around the optical axis of the interference measurement device 30, a motor that applies a rotational force to the holder, and the like.
A part or all of these rotation mechanisms 36a and 36b may be attached to the optical axis tilt cell 35 or to the interference measurement device 30.

The optical axis tilting cell 35 and its rotating mechanisms 36a and 36b are arranged so that the angle change amounts (ΔTL _x , ΔTL _y ) given to the optical axis of the interferometer 30 are controlled by the controller 3.
1 in that it is detected by the folding mirror 192
And the tilt mechanism 13. That is, the rotation mechanism 36
For a and 36b, a motor such as a stepping motor that can control the rotation angle of the holder by the value of the drive signal is used, or a DC motor is used and a sensor that detects the rotation angle of the holder is used. Provided.

With this configuration, the control unit 31 detects the rotation angles (Δθa, Δθb) given to the respective wedge plates 35a, 35b via the rotation mechanisms 36a, 36b, and determines the angle of the optical axis from the rotation angles. Change amount (ΔTL _x , ΔTL _y )
Can be detected. The wedge plates 35a, 35
5b of the rotation angle (Δθa, Δθb) conversion of angle variation of the optical axis to (ΔTL _x, ΔTL _y), each wedge plate 35
This is performed by a predetermined conversion formula according to the inclination angle or the like previously given to the surfaces of a and 35b.

Here, the coordinates (ΔTL _x , ΔTL _y ) indicating the amount of change in the angle of the optical axis are set in the same direction as each data (phase distribution data Ψ (X, Y), etc.). It is represented by the arranged XY coordinates. The information processing device 3
Reference numeral 8 denotes an information processing apparatus such as a computer provided with a CPU, a memory, a hard disk, and the like (not shown), like the information processing apparatus 18.

However, the processing executed by the CPU of the information processing device 38 is the same as the processing executed by the CPU of the information processing device 18 except that the refractive index distribution calculating section 38b is inserted instead of the refractive index distribution calculating section 18b. equal. According to the wedge plate, the tilt angle of the optical axis can be freely changed by its rotation, so that fine adjustment of the tilt angle is easily realized, and based on the driving amount of the wedge plate, Since the amount of change in the tilt angle can be accurately detected, the correction calculation can be performed accurately.

(Operation) FIG. 9 is an operation flowchart of the refractive index distribution measuring system 3 of the present embodiment (and the refractive index distribution measuring system 4 of a fourth embodiment described later).

In FIG. 9, steps that are the same as the steps shown in FIG. 3 are given the same reference numerals, and descriptions thereof will be omitted. Steps S31, S1, S2, S33, S3
Is a process by the control unit 31, step S4 is a process by the phase distribution calculation unit 18a, and steps S5, S6, S37,
S7 is a process by the refractive index distribution calculation unit 38b. First, when the gradient component of the refractive index distribution of the test object 15a is large, as shown in FIG. 10A, the fringe density of the interference fringes generated in the interferometer 30 increases.

If the stripe density is too high, the phase distribution calculator 18
The conversion accuracy to the phase distribution data in a is deteriorated. If the stripe density is too high, the resolution of the image sensor 194 may be exceeded. Therefore, the control unit 31 of the present embodiment sets the interference fringe density to be sufficiently coarse (FIG. 10B) so that phase distribution data is reliably obtained.
The inclination angle of the optical axis is adjusted (Step S31).

Here, whether or not the fringe density has become sufficiently coarse is determined, for example, by performing a process of converting the interference fringe data taken in from the image sensor 194 into phase distribution data and obtaining the obtained phase distribution data. It can be recognized by distinguishing whether the value is significant or not. Also,
The adjustment in step S31 may be performed by driving the tilt mechanism 13, or may be performed by the rotation mechanism 36a,
36b may be driven.

Next, the control section 31 executes step S1 to acquire interference fringe data, and then executes step S2 to rotate the test object 15a by 180 ° around the optical axis. Even in the state after this rotation, there is a high possibility that the fringe density of the interference fringes will be high, so the control unit 31 proceeds to step S3.
1, the fringe density of the interference fringes is sufficiently coarse (FIG. 10).
(C)), to adjust the inclination angle of the optical axis (step S33).

As a result, the measurement in step S1 and the measurement in step S3 are both performed with high accuracy. However, the adjustment in step S33 is performed by the rotation mechanisms 36a and 36b.
This is performed by driving the (optical axis tilting cell 35), and the folding mirror 192 (tilting mechanism 13) is not driven at all. This is because it is necessary to detect the amount of change in the angle of the optical axis (ΔTL _x , ΔTL _y ) generated between the time of measurement in step S1 and the time of measurement in step S3.

That is, in step S33, the control unit 31 performs the adjustment and stores the angle change amount (ΔTL _x , ΔTL _y ) of the optical axis at that time. In the present embodiment, at the time of any of subsequent steps S4 to S7,
For example between steps S6 and S7, the preceding angle change amount stored in step S33 (ΔTL _x, ΔTL _y) correction operation in accordance with applied (step S37).

In step S37, for example,
6 primary component Ψ ₁ (X, Y) (= T _x X +
T _y Y) coefficients T _x of, with respect to T _y, correction calculation expressed by the following equation (6) is applied. Thus, the error superimposed on the primary component Ψ ₁ (X, Y) due to the adjustment in step S33 is reliably removed. _{T x = T x + ΔTL x} , T y = T y + ΔTL y ... (6) above, in this embodiment, even when the inclination component of the refractive index distribution of the object 15a is large, in step S33 Since the adjustment is performed so that the interference measurement can be performed, and the correction calculation process is executed according to the adjustment amount, the measurement of the tilt component can be performed with sufficiently high accuracy.

In the present embodiment, the information passed from the control unit 31 to the refractive index distribution calculation unit 38b is the amount of change in the optical axis angle (ΔTL _x , ΔTL _y ). If the information indicates the amount, the wedge plates 35a, 35
Rotation angle (Δθa, Δθb) given to each of 5b
Alternatively, the values (Sa, Sb) of the drive signals given to each of the rotation mechanisms 36a, 36b may be used. At this time, the angle variation of the optical axis (ΔTL _x, ΔTL _y) conversion to, the control unit 31 without causing the refractive index distribution calculating unit 38b.

In the present embodiment, the control unit 3 stores information on the amount of change in the angle of the optical axis (ΔTL _x , ΔTL _y ).
Although it is set to 1, the refractive index distribution calculator 38b may be used. In the present embodiment, steps S5, S6, S
Instead of step 7, steps S25, S26, and S27 described in the second embodiment may be inserted.

[Fourth Embodiment] Next, a fourth embodiment of the present invention will be described with reference to FIG. 9, FIG. 11, and FIG. Here, only the differences from the third embodiment will be described, and the description of the other parts will be omitted.

(Configuration) FIG. 11 is a view for explaining the refractive index distribution measuring system 4 of the present embodiment. The refractive index distribution measurement system 4 is the same as the refractive index distribution measurement system 3 except that the interference measurement device 30 is provided instead of the interference measurement device 30. The interference measurement device 40 includes the interference measurement device 30
, The optical axis tilting cell 35 and the rotating mechanisms 36a, 3
6b, an angle change detection optical system 45 for detecting an angle change amount of the return mirror 192 is provided, and the control unit 31
Instead of the control unit 41.

The angle change detecting optical system 45 is provided with a light source 45a for irradiating light to the emission system (the surface (back side) opposite to the reflection surface 192a of the reflection mirror 192), and inserted between the light source 45a and the reflection mirror 192. And a lens 45b) that enlarges the diameter of the light beam emitted from the light source 45a and the light reflected on the back side of the folding mirror 192.
Half mirror 45c that deflects in a direction different from the direction of a
And a detection system (a lens 45d for condensing the deflected light and a position sensor 45e disposed on the focal plane of the lens 45d). The position sensor 45e is for converting the light incident position into a signal. Further, it is preferable to provide a reflecting portion on the back surface of the folding mirror 192 so that the light from the light source 45a can be sufficiently reflected.

When the light source 45a is driven by the control unit 41, the light emitted from the light source 45a enters the back side of the folding mirror 192 via the lens 45b and the half mirror 45c, and is reflected by the folding mirror 192. Thereafter, the light is collected by the lens 45d and is
e. The output of the position sensor 45e is
Is input to

If the folding mirror 192 is inclined, the incident position of the light on the position sensor 45e also changes. Therefore, the control unit 41 obtains the change in the inclination angle of the folding mirror 192 from the output change of the position sensor 45e. Is possible. Therefore, according to the tilt mechanism 13 and the angle change detection optical system 45, the same function as the optical axis tilt cell 35 and the rotation mechanisms 36a and 36b in the third embodiment (the tilt of the optical axis of the interference measuring device 40 and the light Shaft angle change).

(Operation) FIG. 9 is an operation flowchart of the refractive index distribution measuring system 4 of the fourth embodiment. The control unit 41 of the present embodiment executes the same procedure as the control unit 31 of the third embodiment, but adjusts the tilt angle of the optical axis in step S33 by driving the tilt mechanism 13, and The control unit 31 is different from the control unit 31 in that the angle change amount of the optical axis is detected via the angle change detection optical system 45.

However, as described above, since the tilting mechanism 13 and the angle change detecting optical system 45 have the same functions as the optical axis tilting cell 35 and the rotating mechanisms 36a and 36b,
As in the third embodiment, even when the gradient component of the refractive index distribution of the test object 15a is large, the measurement of the gradient component can be performed with sufficiently high accuracy. In addition, in the refractive index distribution measurement system 4 of the present embodiment, an angle change detection optical system 55 as shown in FIG.

The angle change detection optical system 55 utilizes the principle of interference, and a part of the light emitted from the light source 55a is
The light is guided to the back side of the return mirror 192 via the lens 55b, the polarization beam splitter 55c, and the Fizeau member 55d. The light reflected on the back side is
The light is deflected in a direction different from that of the light source 55a via the Fizeau member 55d and the polarizing beam splitter 55c,
The light reaches the image sensor 55f via 5e. The light reflected by the Fizeau member 55 d is
b, the light reaches the image sensor 55f via the polarization beam splitter 55c and the lens 55e, and generates interference fringes together with the light reflected on the back side of the return mirror 192.

If the folding mirror 192 is inclined, the interference fringes change. Therefore, the control unit 41 determines from the output change of the image sensor 55f that the folding mirror 192
Can be determined. [Others] Note that some or all of the processing by the control unit, the phase distribution calculation unit, and the refractive index distribution calculation unit in each of the above embodiments may be manually executed. When each part is manually executed, a man-machine interface is provided for a part that must be driven by an operator. For example, as the operation unit, the rotating mechanism 14 and the rotating mechanism 36a,
An operation knob or the like for remotely controlling the holder 36b is provided, and a scale for displaying the rotation angle of the holder, a monitor for displaying interference fringes, and the like are provided as the display unit.

In each of the above embodiments, the rotation angle of the test object 15a is set to 180 ° in order to simplify the calculation. However, if the calculation is allowed to be complicated,
The angle may be set to a predetermined angle other than 180 °. in this case,
In order to remove extra information, the two acquired phase distribution data are compared to separate the component of the pattern that follows the rotation of the test object 15a from the component of the pattern that does not follow, and follow that. Only the primary components need to be extracted from the components of the pattern. This primary component is a gradient component of the refractive index distribution.

The order of the separation and the extraction may be reversed. That is, 1 is obtained from each of the two phase distribution data.
The next component is extracted, and the primary components are compared with each other to separate the component of the pattern that follows the rotation of the test object 15a from the component of the pattern that does not follow, and obtain the component of the pattern that follows the rotation. Just do it. This component is the gradient component of the refractive index distribution.

In each of the above embodiments, the Fizeau interferometer has been described as an interferometer to be mounted on the interferometer. It is. Incidentally, when the Twyman-Green interferometer is applied to the third embodiment, the insertion position of the optical axis tilting cell 35 may be a measurement arm as shown in FIG. 13 or a reference arm as shown in FIG. do it.

When the Mach-Zehnder interferometer is applied to the third embodiment, the insertion position of the optical axis tilting cell 35 is determined by using a measuring arm as shown in FIG. 15 or a reference as shown in FIG. Arms are good. When a Twyman-Green interferometer or a Mach-Zehnder interferometer is applied to the fourth embodiment, the arrangement positions of the angle change detection optical system 45 (55) are as shown in FIGS. Location. Incidentally, in the Mach-Zehnder interferometer shown in FIG.
c becomes unnecessary.

Each of the above embodiments can also be applied to the manufacture of an optical system such as a projection optical system. For example, the gradient component of the refractive index distribution of the optical member to be used for the projection lens is measured by any one of the above embodiments, and the optical member is polished or processed according to the measured gradient component. Adjust the posture and arrangement of the camera. If you do this,
Since the adverse effect of the gradient component of the refractive index distribution on the imaging performance of the projection lens can be suppressed, a high-performance projection optical system can be manufactured.

[0093]

As described above, according to the present invention,
Even if a first-order error component occurs in the measuring instrument, the first-order component (gradient component) of the refractive index distribution can be reliably obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a refractive index distribution measurement system 1 according to a first embodiment.

FIG. 2 is a diagram illustrating a measurement cell 15;

FIG. 3 is an operation flowchart of the refractive index distribution measurement system 1 of the first embodiment.

FIG. 4 is a diagram illustrating the operation of the first embodiment.

FIG. 5 is a diagram illustrating a refractive index distribution measurement system 2 according to a second embodiment.

FIG. 6 is an operation flowchart of the refractive index distribution measurement system 2 of the second embodiment.

FIG. 7 is a diagram illustrating a refractive index distribution measurement system 3 according to a third embodiment.

FIG. 8 is a diagram illustrating an optical axis tilting cell 35;

FIG. 9 is an operation flowchart of the refractive index distribution measurement system 3 of the third embodiment and the refractive index distribution measurement system 4 of the fourth embodiment.

FIG. 10 is a diagram illustrating interference fringes.

FIG. 11 is a diagram illustrating a refractive index distribution measurement system 4 according to a fourth embodiment.

FIG. 12 is a diagram illustrating an angle change detection optical system 55.

FIG. 13 is a diagram showing an example of applying a Twyman Green interferometer to a third embodiment.

FIG. 14 is a diagram showing an application example of a Twyman Green interferometer to a third embodiment.

FIG. 15 is a diagram showing an application example of the Mach-Zehnder interferometer to the third embodiment.

FIG. 16 is a diagram illustrating an application example of a Mach-Zehnder interferometer to a third embodiment.

FIG. 17 is a diagram showing an example of applying a Twyman Green interferometer to a fourth embodiment.

FIG. 18 is a diagram illustrating an application example of a Mach-Zehnder interferometer to a fourth embodiment.

FIG. 19 is a diagram illustrating a conventional method for measuring a refractive index distribution.

[Explanation of symbols]

 1, 2, 3, 4 Refractive index distribution measuring system 10, 20, 30, 40 Interference measuring device 18, 28, 38 Information processing device 11, 21, 31, 41 Controller 12 Moving mechanism 14 Rotating mechanism 13 Tilt mechanism 15 , 1910 measuring cell 15a, 1910a test object 15b, 1910b reference glass 35 optical axis tilting cell 36a, 36b rotating mechanism 45, 55 angle change detecting optical system 45a, 55a light source 45b, 45d, 55b, 55e lens 45c, 61 half Mirror 45e Position sensor 55c Polarizing beam splitter 55d, 191 Fizeau member 60 Mirror 191a Fizeau surface 192a Reflection surface 192 Folding mirror 193 Light source 194 Image sensor 195 Beam splitter 196 Light beam diameter conversion optical system 197 Observation optical system

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (20)

[Claims] 1. A method for measuring a refractive index distribution using a measuring device for measuring a wavefront shape of transmitted light of a test object, wherein a posture of the test object in the measuring device is determined by an optical axis of the measuring device. The first measurement data and the second measurement data output by the measuring instrument before and after the change to a state rotated around by a predetermined angle, and the first measurement data and the second measurement data are acquired. 2. A method of measuring a refractive index distribution, wherein a difference from the measurement data of No. 2 is obtained as information indicating a primary component of the refractive index distribution of the test object. 2. The method for measuring a refractive index distribution according to claim 1, wherein the predetermined angle is set to 180 °. 3. The method of measuring a refractive index distribution according to claim 2, wherein a difference between the first measurement data and the second measurement data is obtained, and a first-order component of the obtained difference is used as the first component. A method for measuring a refractive index distribution, comprising extracting as information indicating a primary component of a refractive index distribution of a specimen. 4. The method of measuring a refractive index distribution according to claim 2, wherein a primary component of the first measurement data and a primary component of the second measurement data are extracted and extracted. A method for measuring a refractive index distribution, wherein a difference between the primary components of the test object is obtained as information indicating a primary component of the refractive index distribution of the test object. 5. The method for measuring a refractive index distribution according to claim 1, wherein the measuring device has a predetermined wavefront shape with the measuring light transmitted through the test object. An interference optical system that interferes with light and detects interference fringes generated by the interference as information indicating the wavefront shape of the measurement light, and an inclination angle of an optical axis of the measurement light and / or an optical axis of the reference light. Using an interference measuring device having an optical axis tilting mechanism that changes the tilt angle, when the attitude is changed, by driving the optical axis tilting mechanism, the interference generated before and after the change, respectively. The fringe density of the fringes is kept coarse enough to be detectable, and according to the amount of change given to the tilt angle of the optical axis by driving the optical axis tilting mechanism, for the process of obtaining the information or the result obtained, Performing correction operation Method of measuring the refractive index profile, wherein. 6. The method of measuring a refractive index distribution according to claim 5, wherein a wedge plate inserted into a measurement arm and / or a reference arm of the interference optical system is used as the optical axis tilting mechanism. Of measuring the refractive index distribution. 7. The method for measuring a refractive index distribution according to claim 5, wherein, as the optical axis tilting mechanism, a reflecting surface that deflects the measuring light and / or the reference light of the interference optical system, and the reflecting surface is tilted. A method for measuring a refractive index distribution, characterized by using a mechanism for causing a refractive index distribution. 8. The apparatus according to claim 1, wherein the test object is provided between two reference glasses via a liquid.
The method for measuring a refractive index distribution according to any one of claims 1 to 7. 9. The method according to claim 8, wherein the refractive index of the reference glass and the refractive index of the liquid are substantially the same as the average refractive index of the test object. 10. A measuring device for measuring a wavefront shape of transmitted light of a test object, a control unit for driving and controlling each unit of the measuring device, and an operation unit for performing an operation on measurement data output by the measuring device A measuring device for measuring the refractive index distribution, comprising: a posture changing mechanism for changing a posture of the test object to a state rotated by a predetermined angle around an optical axis of the measuring device. The control unit changes the posture of the test object by driving the posture changing mechanism, and outputs first measurement data and second measurement data output by the measuring device before and after the change. Data, and the arithmetic unit obtains a difference between the first measurement data and the second measurement data as information indicating a primary component of a refractive index distribution of the test object. For measuring refractive index distribution. 11. The apparatus for measuring a refractive index distribution according to claim 10, wherein the predetermined angle is set to 180 °. 12. The apparatus for measuring a refractive index distribution according to claim 11, wherein the arithmetic unit calculates a difference between the first measurement data and the second measurement data, and calculates a first order of the calculated difference. An apparatus for measuring a refractive index distribution, wherein a component is extracted as information indicating a primary component of a refractive index distribution of the test object. 13. The apparatus for measuring a refractive index distribution according to claim 11, wherein the arithmetic unit extracts a primary component of the first measurement data and a primary component of the second measurement data. And measuring a difference between the extracted primary components as information indicating a primary component of the refractive index distribution of the test object. 14. The apparatus for measuring a refractive index distribution according to claim 10, wherein the measuring device has a predetermined wavefront shape with the measuring light transmitted through the test object. An interference optical system that interferes with light and detects interference fringes generated by the interference as information indicating the wavefront shape of the measurement light; and an inclination angle of an optical axis of the measurement light and / or an optical axis of the reference light. An optical axis tilting mechanism that changes the tilt angle; and a detecting unit that detects an amount of change in the tilt angle generated in the optical axis by driving the optical axis tilting mechanism. By driving the optical axis tilting mechanism, each of the fringe densities of the interference fringes before and after the change is maintained at a predetermined value or less, and the calculation unit responds to a change amount detected by the detection unit. And said To result process or determined seek distribution, the refractive index distribution, characterized in that applying correction calculation measurement device. 15. The apparatus for measuring a refractive index distribution according to claim 14, wherein the optical axis tilting mechanism comprises a wedge plate inserted into a measuring arm and / or a reference arm of the interference optical system. For measuring refractive index distribution. 16. The apparatus for measuring a refractive index distribution according to claim 14, wherein the optical axis tilting mechanism is configured to deflect the measuring light and / or the reference light of the interference optical system, and to tilt the reflecting surface. A refractive index distribution measuring device, comprising: 17. The refractive index distribution according to claim 10, wherein the specimen is provided between two reference glasses via a liquid. Measuring device. 18. The apparatus according to claim 17, wherein the refractive index of the reference glass and the refractive index of the liquid are substantially the same as the average refractive index of the test object. 19. The method according to claim 1, wherein a first-order component of the refractive index distribution of the optical member constituting the optical system is measured by the method for measuring a refractive index distribution. And adjusting or processing the optical system according to the primary component of the refractive index distribution. 20. An optical member having a primary component of a refractive index distribution measured in advance by the method for measuring a refractive index distribution according to claim 1, wherein the optical member has An optical system having a shape and / or arrangement corresponding to a primary component.