JPH1090117A - Method and instrument for measuring refractive index distribution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the refractive index distribution on a phase object even when the quantity of transmitted wave face is large and the pitch of interference fringes is short. SOLUTION: Coherent light from the same light source 1 is split into a reference wave (a) which becomes a standard and a wave (b) to be inspected which is transmitted through an object O to be inspected and the wave (b) is further split into waves b11 and b12 through a light splitter 21. Then a shearing interference image is formed on a second detector by superimposing the wave b12 after a shear is given to the transmitted wave face of the wave b11 in the direction perpendicular to the optical axis. When the interference image is formed in such a way, the refractive index distribution on the object O can be measured even when the object transmits a large quantity of front waves and makes the pitch of shearing interference fringes shorter, because the shearing interference fringes become rougher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an optical element, a liquid,
Also, the present invention relates to an apparatus for measuring a phase object such as a gas, and more particularly to an apparatus suitable for measuring a refractive index distribution in a phase object by analyzing interference fringes.

[0002]

2. Description of the Related Art In recent years, plastics have been increasingly used as materials for optical lenses used in optical devices such as laser printers and cameras. Compared to a glass polished lens, a plastic molded lens has advantages in that it is superior in cost reduction and manufacturability of an aspherical lens, and is inexpensive.

[0003] On the other hand, however, the refractive index distribution is unstable in production as compared with a glass lens, and non-uniformity may occur inside the lens. Non-uniformity inside the lens has a great effect on optical characteristics, leading to deterioration of image quality and blurring. Therefore, it is necessary to measure the refractive index distribution inside the lens three-dimensionally with high accuracy and evaluate the homogeneity of the optical lens.

As a method of measuring the refractive index of an optical lens, a method of measuring a refractive angle by a V-block method or the like using a precision differential refractometer or the like to obtain a refractive index, or an interference method such as a Twyman-Green interferometer or the like. There is a method of measuring the refractive index from the interference fringes using an interferometer, and the method of measuring optical homogeneity is based on the analysis of interference fringe images using an interferometer such as a Fizeau interferometer or a Mach-Zehnder interferometer. There is known a method of measuring a transmitted wavefront and obtaining optical homogeneity from a refractive index distribution.

However, in any of the above methods, the test object must be processed into a predetermined shape, and the optical element to be measured must be destroyed. Also, the refractive index distribution obtained from the transmitted wavefront becomes an average value integrated in the optical path traveling direction, and the three-dimensional spatial refractive index distribution is measured to specify the non-uniform refractive index part three-dimensionally. Can not.

Accordingly, the applicant of the present invention has filed Japanese Patent Application No.
In -203502, a test object is immersed in a test solution and rotated about an axis orthogonal to the optical axis, interference fringes are analyzed at each of a plurality of rotation angle positions, and a transmitted wavefront is calculated from these interference fringes. A method of calculating the quantity, performing a first-order Fourier transform on the quantity, and further performing a two-dimensional inverse Fourier transform to obtain a three-dimensional refractive index distribution was proposed.

[0007]

According to the method and apparatus for measuring the refractive index distribution according to the above-mentioned application, there is an advantage that the measurement can be performed with high accuracy even if the refractive index difference from the sample solution is small. . However, when measuring a phase object having a large amount of transmitted wavefront, such as when the refractive index difference is large, the number of interference fringes increases, which may exceed the resolution of the detector.

The present invention has been conceived in view of the above facts, and it is an object of the present invention to provide a method and an apparatus for measuring a refractive index distribution capable of measuring a large amount of transmitted wavefront and a fine pitch of interference fringes. And

[0009]

In order to achieve the above object, a measuring method according to the present invention divides a test wave consisting of coherent light transmitted through a test object into two light beams, and forms a wavefront of one of the light beams. Are shifted in the direction perpendicular to the optical axis and then superimposed to form interference fringes due to sharing interference, and the interference fringes are analyzed to measure the refractive index distribution of the test object.

In addition, the test object is transmitted while rotating the test object about an axis perpendicular to the optical axis, a plurality of interference fringes are formed, each transmitted wavefront is measured, and reconstruction is performed using CT analysis. By doing so, it is also possible to measure the three-dimensional refractive index distribution of the test object.

A measuring apparatus according to the present invention includes a light splitter for splitting a test wave composed of coherent light transmitted through a test object into two light beams, and is disposed in each of the light beams split by the light splitter. It is characterized by having a reflecting device and a sharing unit for shifting the wavefront of one light beam in a direction perpendicular to the optical axis.

Alternatively, an interferometer that divides coherent light from the same light source into a reference wave and a test wave, and forms an interference fringe by combining the test wave with the reference wave after passing through the test object; It is characterized by having a sharing interferometer that divides the detection into two light beams, and superimposes the wavefront of one of the light beams in a direction perpendicular to the optical axis to form interference fringes.

The sharing interferometer receives a test wave from the interferometer and divides the test wave into two light beams, and two light splitters placed in an optical path of each of the two split light beams. It is possible to adopt a configuration having a reflection device and a sharing unit that moves one of the reflection devices in a direction perpendicular to the optical axis.

Alternatively, the sharing interferometer receives a test wave from the interferometer and splits the test wave into two light beams, and a beam splitting / superimposing beam splitter; It has two placed corner cubes, and a sharing unit that moves one of the corner cubes in a direction perpendicular to the optical axis, and the light flux reflected from each corner cube is split by the light splitting / superimposing beam splitter. A configuration may be adopted in which the above-mentioned sharing interference fringes are formed by superimposition.

Further, the interferometer comprises a Mach-Zehnder interferometer, an optical splitter for splitting coherent light from the same light source into a reference wave and a test wave, and an optical superposition device for superposing the reference wave and the test wave. It is desirable to adopt a configuration using a polarizing beam splitter.

Alternatively, an interferometer that divides coherent light from the same light source into a reference wave and a test wave, and transmits or reflects the test wave and then weighs the reference wave, and two of the test waves And a sharing interferometer that forms an interference fringe by shifting the wavefront of one of the light beams in a direction perpendicular to the optical axis to form an interference fringe.The interferometer and the sharing interferometer share the same configuration. Configuration.

Also, a light source of the coherent light, a light splitter for splitting the coherent light into a reference wave and a test wave, a beam splitter disposed in an optical path of the reference wave, and a light transmitted through the beam splitter. A movable reflecting means arranged in the optical path of the reference wave and movable in the optical axis direction and the direction perpendicular to the optical axis by the driving means, and a fixed reflecting means arranged in the optical path of the test wave emitted from the optical splitter; A beam splitter within a test wave disposed in an optical path reflected by the fixed reflecting means, and a light superposition for superimposing and outputting a test wave from the beam splitter within the test wave and a reference wave from the movable reflecting means. A beam splitter for imaging, an imaging lens arranged in an optical path of the superimposed test wave and the reference wave, and forming an interference fringe, and a first detector arranged on the image plane thereof. The beam transmitted through the inner beam splitter The wave and the test wave reflected by the beam splitter in the test wave and passing through the beam splitter and the movable reflecting means are superposed by the beam superimposing beam splitter, and are arranged in an optical path which is emitted by causing interference and is shared. It is also possible to adopt a configuration having an imaging lens for forming an interference fringe and a second detector arranged on the imaging plane.

In the above, it is desirable to have a configuration having a turntable for rotating the test object about an axis perpendicular to the optical axis.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a view showing one embodiment of the refractive index distribution measuring device of the present invention. The apparatus shown in FIG. 1 is configured by a combination of a Mahachender interferometer A and a sharing interferometer B. The Mach-Zehnder interferometer A includes a light source 1 that emits laser light as coherent light, a beam expander 3, a light splitter 5 including a polarizing beam splitter,
Reflector 7 consisting of a mirror placed in the optical path of the reference wave
A reflection device / light splitter 9 including a beam splitter for splitting a test wave into two light beams; a polarization beam splitter as an optical superimposing device 11; an imaging lens 13; and an interference fringe detector 15 including a CCD or the like. , A polarizer 17.

The laser beam emitted from the light source 1 is expanded in beam diameter by the beam expander 3, and is refracted at right angles by the beam splitter 5 to become a reference beam a. The laser beam is split into another laser beam which becomes a test wave b passing through the phase object as O. The reference wave a and the test wave b are set to be approximately 1: 3.

The reflection device 7 is supported by an electric-displacement conversion element 19 such as a piezo element, and is arranged so that the optical path length of the reference wave a can be changed in the order of wavelength in order to perform interference fringe analysis by the phase shift method. Have been.

The reference wave a is reflected by the reflection device 7 and reaches the optical superimposer 11, while the other test wave b transmits through the test object O and a part b2 is reflected by the reflection device / light splitter 9, Although the light reaches the optical superimposer 11 and overlaps with the reference wave a, the optical path length between the reference wave a and the test wave b is n
It is adjusted so as to have a phase difference of π / 2.

The reference wave a and the test wave b2 are superimposed, emitted from the optical superimposer 11, incident on the imaging lens 13, and form interference fringes on the imaging surface of the interference fringe detector 15. A linear CC arranged in a direction perpendicular to the interference fringes
D or an array sensor is used.

On the other hand, the light beam b1 transmitted through the reflection device / light splitter 9 enters the sharing interferometer B. The sharing interferometer B converts the incident test wave b1 into two light beams b1.
1. A light splitter 21 composed of a beam splitter for splitting into two beams, b12, reflection devices 23 and 25 composed of mirrors arranged in each of these two light fluxes, an optical superposition device 27 using a beam splitter, and an imaging lens 29 and the second detector 31
And

As the second detector 31, an area image sensor such as a CCD or a line sensor arranged in a direction orthogonal to the interference fringes is used. Also, the reflection device 25
Has a sharing unit 33 and can move the wavefront of the test wave b11 in a direction perpendicular to the optical axis. This has a configuration using a piezo element or the like, like the electric-displacement conversion element 19.

The test wave b1 transmitted through the test object O and further transmitted through the reflection device / light splitter 9 is re-transmitted by the light splitter 21 to b.
11 and b12.
After being reflected at 25, the light is superimposed again by the optical superimposing device 27. At this time, the sharing unit 33 gives a shear (lateral displacement) to the reflection device 25 and shifts the wavefront of the test wave in a direction perpendicular to the optical axis, so that this portion causes sharing interference.

With the above configuration, the apparatus shown in FIG. 1 can perform both the measurement of the interference fringes by the Mach-Zehnder interferometer A and the measurement of the interference fringes by the sharing interferometer B. Therefore, when measuring a phase object having a small transmitted wavefront amount (approximately several λ or less), the fringe analysis of the interference fringe of the Mach-Zehnder interferometer A is performed by the first detector 15 by the phase shift method.

When measuring a phase object having a large amount of transmitted wavefront, the number of interference fringes is large and the pitch of the fringes is small, so that the resolution of the first detector 15 may be exceeded. On the other hand, since the sharing interference is interference between the test waves, there is an effect of lowering the sensitivity. That is, the transmitted wavefront on the first detector 31 is reduced, and the first detector 15 can measure even a phase object whose fringe cannot be analyzed.

Therefore, the amount of transmitted wavefront is large and the first detector 1
In the case where the resolution exceeds 5, the interference fringes are not measured by the Mach-Zehnder interferometer A.
The wavefront ΔW (y) obtained by the above is integrated in the length direction y of the line sensor of the second detector 31 to analyze the wavefront by the following equation (1). W (y) = (1 / S) ∫ΔW (y) dy (1)

FIG. 2 shows a measuring apparatus according to a second embodiment of the present invention. In the sharing interferometer, a sharing interferometer B2 is formed by using two corner cubes 41 and 43. One corner cube 43 is provided with a sharing unit 33.

The test wave b transmitted through the reflection device / light splitter 9
1 is a beam splitter 45 for light division and superposition again b1
The light is divided into two light beams 1 and b12, reflected by the corner cubes 41 and 43 placed in the respective optical paths, returned, superimposed by the light splitting / superimposing beam splitter 45, and passed through the imaging lens 29 for the second detection. It is taken into the vessel 31. At this time, sharing interference is caused by giving a share to one corner cube 43 by the sharing unit 33. The measurement according to the invention is the same as the device of FIG.

FIG. 3 shows a measuring apparatus according to a third embodiment of the present invention.
This is an example in which the interferometer A2 also serves as a part of the sharing interferometer B3 using a polarizing beam splitter to reduce the size of the apparatus. In FIG. 3, the reflection device / light splitter 9 of the Mach-Zehnder interferometer A2 also plays the role of the light splitter 21 in FIG. The reflection device 23 in FIG. 1 is also used by the optical superposition device 11. Further, a １ ／ wavelength plate 61 is provided between the reflection device / light splitter 9 and the optical superposition device 11.

Referring to FIG. 4, explanation will be given on the Mahach-Zehnder interference in the apparatus shown in FIG. The laser light from the light source 1 is expanded by the beam expander 3, and the reference light a
And the test wave b. The test wave b passes through the test object O and reaches the reflection device / light splitter 9, where it is split into a test wave b1 transmitted and a test wave b2 reflected. The reflected test wave b2 passes through the quarter-wave plate 61 and reaches the optical superimposer 11. The optical superimposer 11 is a polarization beam splitter, and the test wave b2 is transmitted through the quarter-wave plate 61 and is circularly polarized. Therefore, one linearly polarized light component is transmitted and becomes the test wave b21, and the other is orthogonal. The reflected linearly polarized light component becomes the test wave b22.

The reference wave a emitted from the light splitter 5 is reflected by the reflecting device 7, is totally reflected by the optical superimposing device 11 composed of a polarizing beam splitter, is superimposed on the test wave b21, and forms an image from the polarizer 17. The light reaches the first detector 15 via the lens 13. The electric-displacement conversion element 19 of the reflection device 7 adjusts the optical path length of the reference wave a so that there is a phase difference of nπ / 2. Thereby, interference fringes are formed on the first detector 15.

The sharing interference will be described with reference to FIG. The test wave b transmitted through the test object O is split into a test wave b1 transmitted by the reflection device / optical splitter 9 and a test wave b2 reflected. The reflected test wave b2 passes through the 波長 wavelength plate 61 and reaches the optical superimposer 11 as described with reference to FIG.
The test wave b22 is reflected. The test wave b22 reaches the optical superimposer 65, where the test wave b reflected by the reflection device 63
Superimposed on 1. The sharing unit 33 gives the reflection device 25 a shear (lateral displacement) to cause sharing interference.

According to the above configuration, in the sharing interferometer, the distance from the test object O to the second detector 31 can be reduced, so that the imaging magnification can be easily increased. Further, the use of the polarization plane of the polarization beam splitter BS has an isolating effect, so that crosstalk does not occur.

FIG. 6 shows a fourth embodiment of the present invention, in which a Mach-Zehnder interferometer and a sharing interferometer are combined so as to overlap. This device includes a laser light source 1, a beam expander 3, a light splitter 5 composed of a polarization beam splitter, a polarization beam splitter 71 placed in an optical path of a reference wave a, and an optical path transmitted therethrough. , A fixed reflecting means 82 fixed in the optical path of the test wave b, and a beam splitter 7 in the test wave placed in the optical path of the test wave b reflected by the reflecting device.
3 and a beam splitter 77 for light superimposition comprising a polarizing beam splitter for superimposing a light beam from the beam splitter 73 within the test wave and a light beam from the movable reflecting means 81.
A 波長 wavelength plate 75 disposed between the beam splitter 73 within the test wave and the beam splitter 77 for optical superposition,
It comprises polarizers 17 and 67, imaging lenses 13 and 29, a first detector 15 and a second detector 31.

The laser light emitted from the light source 1 is expanded by the beam expander 3 and split by the light splitter 5 such that the ratio between the reference wave a and the test wave b becomes approximately 1: 3. The transmitted light becomes the reference wave a, and the reflected light becomes the test wave b passing through (the test object O).

Referring to FIG. 7, the description will be made of the Mahach-Zehnder interference. The test wave b transmitted through the test object O is fixed reflection means 8
2 and the transmitted light b1: reflected light b2 is split into 2: 1 by the beam splitter 73 in the test wave. The test wave b1 transmitted through the beam splitter 73 in the test wave is circularly polarized by the quarter-wave plate 75, and a component b12 oscillating in the direction perpendicular to the paper is reflected by the beam splitter 77 for superimposing light, and is orthogonal to this. The component b11 is transmitted. On the other hand, the reference wave a transmitted through the light splitter 5 and the polarization beam splitter 71 and reflected by the movable reflecting means 81 reaches the light superimposing beam splitter 77, where it is superimposed on the test wave b12, and the polarizer 17 is connected. After passing through the image lens 13, the light reaches the first detector 15. The movable reflecting means 81 includes a driving means 83 capable of moving the movable reflecting means 81 in the optical axis direction in the order of wavelength using a piezo element or the like. And the first detector 1
An interference fringe is imaged on 5.

The sharing interference will be described with reference to FIG. First, the test wave b is divided into b1 that passes through the beam splitter 73 within the test wave and b2 that is reflected. The reflected test wave b2 is the polarized beam splitter 7
1 and the movable reflection means 81, reach the beam splitter 77 for optical superimposition, where it is reflected toward the second detector 31.

The test wave b1 transmitted through the beam splitter 73 in the test wave is circularly polarized by the quarter-wave plate 75, reaches the beam splitter 77 for optical superposition, and the test wave b12 is reflected as described above, A test wave b1 having a component orthogonal to the detection wave
1 is transmitted and superimposed on the test wave b2.

The driving means 83 is capable of moving the movable reflecting means 81 in a direction perpendicular to the optical axis, and imparts a shear to the wavefront of the test wave b2, thereby forming a sharing interferometer.
The second detector 31 can measure sharing interference fringes.

In the apparatus shown in FIG. 6, one phase modulator is used by two interferometers, so that one mechanical movable part is reduced and the stability of the whole apparatus is increased. Further, a normal beam splitter may be used instead of the polarization beam splitters 5, 71, 77, but the polarization beam splitter has an isolation effect and can prevent crosstalk.

In each of the above embodiments, it is possible to three-dimensionally reconstruct the refractive index of the test object using CT (computer tomography) analysis. Here, an apparatus capable of performing CT analysis using the configuration of FIG. 9 will be described. This is a diversion of the device of FIG.

The test object 0 is in a container 91 immersed in a test solution S having a refractive index substantially equal to that of the test object, and an optical flat 97 having good surface precision is provided on an entrance window 93 and an exit window 95 of a light beam. , 99 are used. The test object O is installed on a turntable 101 having a rotation axis P perpendicular to the optical axis, and the container 91 has a structure in which the test object 0 can rotate around the axis P in a fixed state. ing.

The transmitted wavefront is measured without setting the test object O in advance, and a steady error component of the apparatus itself is eliminated. Next, the test object O is set on the turntable 101 and the transmitted wavefront is measured. At this time, if the refractive index of the test object O is completely uniform and equal to the refractive index of the test solution S, the fringe analysis result becomes zero. However, when the test object O is slightly deviated from the refractive index of the test solution S, the following relational expression holds.

Φ (y) = (2π / λ) ∫Δn (x, y) dx (3) where φ (y): transmitted wavefront (rad) Δn (x, y): sample O and sample B Λ: wavelength of laser light

A light source 1 is applied to an object O having a non-uniform refractive index distribution.
Of the first detector 15 or the second detector 3
The refractive index distribution can be obtained from the obtained transmitted wavefront by taking in the interference fringes generated on 1 and performing fringe analysis.

However, the result obtained by one measurement is the transmitted wavefront integrated in the thickness direction (x direction) of the test object O. Therefore, in order to determine the spatial position of the non-uniform portion, it is necessary to rotate the test object and perform the same fringe analysis a plurality of times. That is, the test object is rotated around the (relative) z-axis with respect to the optical axis of the interferometer, measured over a range of 180 degrees (or 360 degrees) in the incident direction, and re-combined on a computer. The three-dimensional refractive index distribution of the specimen can be measured. X-ray CT (Computed Tomography) is a processing method on a computer.
y) Use an analysis technique. FIG. 10 shows the calculation procedure, and FIG. 11 shows the concept of Fourier transform.

In FIGS. 10 and 11, the transmitted wavefront data P (y, φ) incident from the direction of the angle φ is subjected to one-dimensional Fourier transform. After transforming the Fourier-transformed polar coordinate data of each section into orthogonal coordinates, a two-dimensional inverse Fourier transform is performed, whereby the two-dimensional refractive index distribution of the test object can be reconstructed. The refractive index distribution of the test object O can be measured by outputting the reconstructed two-dimensional refractive index distribution on a display or the like and displaying it, or by using an appropriate output means.

In this measuring apparatus, simultaneous measurement can be performed by using a Mahachenda interferometer and a sharing interferometer (first and second detectors). When the number of interference fringes is small, the first detector 15 measures the number of interference fringes based on the phase shift. When the number of interference fringes is large and exceeds the resolution of the first detector 15, analysis is performed by using the second detector 31 by sharing interference. 2
By combining two interferometers, an object having a large difference in refractive index can be measured with high resolution. Alternatively, a three-dimensional refractive index can be measured by placing the test object on a turntable without rotating the test solution S, and forming and measuring interference fringes while rotating.

[0052]

As described above, according to the present invention, even in the case where the number of fringes exceeds the resolution due to the large number of fringes in the ordinary interference fringe measuring method, the measurement can be performed by sharing interference. be able to. Also, when measuring while rotating the test object around the rotation axis perpendicular to the optical axis,
The three-dimensional refractive index of the test object can be measured by the CT analysis.

Further, if an apparatus capable of measuring both the Mach-Zehnder interference and the shearing interference is used, the measurement can be performed arbitrarily with one apparatus, and a variety of specimens can be measured. Further, both interferences can be measured at the same time, and higher resolution and higher dynamic range measurement can be performed.

By using the corner cube, it is possible to set the share amount independently of the piezo drive. Another feature is that the share amount can be easily determined. When the interferometer and the sharing interferometer are partially overlapped, the size of the device can be reduced. Therefore, the distance from the test object to the detector can be shortened, so that the imaging magnification can be easily increased. Performing the phase modulation of the Mach-Zehnder interferometer and the sharing interferometer by one phase modulator increases the safety of the device and lowers the cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of an apparatus for measuring a refractive index distribution according to the present invention.

FIG. 2 is a diagram showing the configuration of a second embodiment of the apparatus for measuring the refractive index distribution of the present invention.

FIG. 3 is a diagram showing a configuration of a third embodiment of the apparatus for measuring a refractive index distribution according to the present invention.

FIG. 4 is a diagram illustrating a method for measuring interference fringes with the apparatus of FIG. 3;

FIG. 5 is a diagram illustrating a method for measuring a shearing interference fringe with the apparatus of FIG. 3;

FIG. 6 is a diagram showing the configuration of a fourth embodiment of the apparatus for measuring a refractive index distribution according to the present invention.

FIG. 7 is a diagram illustrating a method for measuring interference fringes with the apparatus of FIG. 6;

FIG. 8 is a diagram illustrating a method for measuring a shearing interference fringe with the apparatus of FIG. 3;

FIG. 9 is a diagram showing a configuration of a first embodiment of an apparatus for measuring a refractive index distribution according to the present invention.

FIG. 10 is a flowchart showing a method of CT analysis.

FIG. 11 is a diagram illustrating the principle of CT analysis.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light source 5 light splitter 11 light superimposing device 15 first detector 17 imaging lens 21 light splitter 23, 25 reflecting device 29 imaging lens 33 sharing unit 41, 43 corner cube 45 beam splitter 71 beam splitter 73 test wave Inner beam splitter 77 Beam splitter for superimposing light 81 Movable reflecting means 82 Fixed reflecting means 83 Driving means 101 Turntable A Interferometer B, B2, B3 Sharing interferometer O Test object a Reference wave b Test wave

Claims (10)

[Claims] 1. A test wave comprising coherent light transmitted through a test object is divided into two light beams, and the wavefront of one of the light beams is shifted in a direction perpendicular to the optical axis and then superimposed, and then superimposed to cause interference fringes due to sharing interference. And measuring the refractive index distribution of the test object by analyzing the interference fringes. 2. A test wave is transmitted while rotating the test object about an axis perpendicular to the optical axis, a plurality of interference fringes are formed, each transmitted wavefront is measured, and reconstruction is performed using CT analysis. The method of measuring a refractive index distribution according to claim 1, wherein the three-dimensional refractive index distribution of the test object is measured by performing the measurement. 3. A light splitter for splitting a test wave composed of coherent light transmitted through a test object into two light beams, and a reflecting device disposed in each light beam split by the light splitter. A sharing unit that shifts the wavefront of the luminous flux in a direction perpendicular to the optical axis;
An apparatus for measuring a refractive index distribution, comprising: 4. An interferometer that divides coherent light from the same light source into a reference wave and a test wave, and that the test wave passes through the test object and weighs with the reference wave to form interference fringes. An apparatus for measuring a refractive index distribution, comprising: a sharing interferometer that divides detection into two light beams, and superimposes the wavefront of one of the light beams in a direction perpendicular to the optical axis to form interference fringes. 5. The sharing interferometer receives a test wave from the interferometer and splits the test wave into two light beams, and is placed in an optical path of each of the two split light beams. 2
The refractive index distribution measuring device according to claim 4, further comprising: one reflecting device; and a sharing unit that moves one of the reflecting devices in a direction perpendicular to the optical axis. 6. A beam splitter for splitting and superposing a beam splitter for receiving a test wave from the interferometer and splitting the test wave into two light beams, wherein the sharing interferometer is provided in an optical path of each of the two light beams. It has two placed corner cubes, and a sharing unit that moves one of the corner cubes in a direction perpendicular to the optical axis, and the light flux reflected from each corner cube is split by the light splitting / superimposing beam splitter. 4. An apparatus according to claim 3, wherein said shearing interference fringes are formed by superimposition. 7. An optical splitter for splitting coherent light from the same light source into a reference wave and a test wave, an optical splitter for superposing the reference wave and the test wave, wherein the interferometer comprises a Mach-Zehnder interferometer. 7. The apparatus according to claim 4, wherein a polarization beam splitter is used. 8. An interferometer that divides coherent light from the same light source into a reference wave and a test wave, and transmits or reflects the test wave to the test object and then weighs the reference wave. And a sharing interferometer that forms an interference fringe by shifting the wavefront of one of the light beams in a direction perpendicular to the optical axis to form an interference fringe.The interferometer and the sharing interferometer share the same configuration. An apparatus for measuring a refractive index distribution. 9. A light source for coherent light, a light splitter for splitting the coherent light into a reference wave and a test wave, a beam splitter disposed in an optical path of the reference wave, and a light transmitted through the beam splitter. A movable reflecting means arranged in the optical path of the reference wave and movable in the optical axis direction and the direction perpendicular to the optical axis by the driving means, and a fixed reflecting means arranged in the optical path of the test wave emitted from the optical splitter; A beam splitter within a test wave disposed in an optical path reflected by the fixed reflecting means, and a light superposition for superimposing and outputting a test wave from the beam splitter within the test wave and a reference wave from the movable reflecting means. A beam splitter for imaging, an imaging lens arranged in an optical path of the superimposed test wave and the reference wave, and forming an interference fringe, and a first detector arranged on the image plane thereof. The test wave transmitted through the inner beam splitter The test wave reflected by the beam splitter within the test wave and passing through the beam splitter and the movable reflecting means is superimposed by the light superimposing beam splitter, and is arranged in an optical path which is emitted by causing shearing interference and is emitted by a sharing interference fringe. A measuring apparatus for a refractive index distribution, comprising: an image forming lens for forming an image; and a second detector arranged on the image forming surface of the image forming lens. 10. The apparatus according to claim 3, further comprising a turntable for rotating the test object around an axis perpendicular to the optical axis.
The measurement device for refractive index distribution according to any one of the above.