TWI871125B - Shearing interference measurement method and shearing interference measurement device - Google Patents

Abstract

[Topic] In order to efficiently measure the aberration of optical elements, the interference wavefront measurement that was previously performed multiple times can be performed once during the shearing interferometer measurement. [Solution] In a shearing interferometer that splits a beam between a light source and a measurement object lens and irradiates the split beam to the measurement object lens to cause interference, the split beam is split by an aperture plate disposed between the light source and the measurement object lens; the aperture plate is provided with three or more apertures that are not in a straight line.

Description

Shearing interference measurement method and shearing interference measurement device

The present invention relates to a shearing interferometer measurement method and a shearing interferometer measurement device. More specifically, the present invention relates to a shearing interferometer measurement method and a shearing interferometer measurement device that can obtain a shearing interferometer point pattern containing information in two or more directions at one time by irradiating a light beam from a light source with three or more apertures to a measurement object lens.

Currently, the miniaturization and high-precision of optical components used in smartphones and cameras continue to advance.

Therefore, there is an increasing demand for efficient and high-precision measurement of aberrations (wavefront shapes from optical elements when light is irradiated thereon) of optical elements such as lenses and mirrors.

Conventionally, such aberrations have been measured using, for example, a Shack-Hartmann sensor or an interferometer.

For example, the Shack-Hartmann sensor, as described in Japanese Unexamined Patent Application Publication No. 2013-246016 (Patent Document 1), analyzes the image of output light that has passed through a microlens array to obtain aberrations.

The interferometer includes, for example, a Michaelson interferometer and a Fizeau interferometer as described in JP-A-2011-504234 (Patent Document 2), or a shearing interferometer as described in JP-A-2005-183415 (Patent Document 3).

Among them, the McArthur interferometer uses a beam splitter to split the light beam into two, and then recombines the two beams to interfere. In the Fizeau interferometer, the incident laser beam passes through a diverging lens, a beam splitter, and a collimating lens to become parallel light and reach a high-precision reference plate (flat glass plate).

Among interferometers, a shearing interferometer uses an amplitude splitting element (beam splitter, optical plate, diffraction grating, etc.) to split a wavefront, with the same wavefront shape, to create two (generally multiple) parallel light beams whose optical axes are offset in the vertical direction. The wavefront shape of the original light beam is determined from the fringe information formed by the interference of the two light beams after passing through the specimen.

Next, in shearing interferometers, there are also methods that use a method of splitting the light beam after passing through the object to be tested and interfering. [Prior art literature] [Patent literature]

[Patent Document 1] Japanese Patent Publication No. 2013-246016 [Patent Document 2] Japanese Patent Publication No. 2011-504234 [Patent Document 3] Japanese Patent Publication No. 2005-183415 [Non-patent Document]

[Non-patent document 1] F. Ricci, W. Loffler, and M.P. van Exter: Instability of higher-order optical vortices analyzed with a multi-pinhole interferometer, 24 September 2012/ Vol. 20, No. 20/OPTICS EXPRESS 22961 [Non-patent document 2] Samuel A. Eastwood, Alexis I. Bishop, Timothy C. Petersen, David M. Paganin, and Michael J. Morgan: Phase measurement using an optical vortex lattice produced with a three-beam interferometer, 18 June 2012/Vol. 20, No. 13/OPTICS EXPRESS 13947 [Non-patent document 3] J. H. Brunning et al.: Digital wavefront measuring interferometer for testing optical surfaces and lenses, Appl. Opt., 13, 2693/2703 (1974). [Non-patent document 4] Junichi Kato: Real-time interference pattern analysis and its application, Journal of the Society for Precision Engineering, 64(9), 1289/1293 (1998). [Non-patent document 5] M. Takeda, H. Ina, and S. Kobayashi: Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry, J. Opt. Soc. Am., 72, 156/160 (1982). [Non-patent document 6] S. Toyooka and M. Tominaga: Spatial fringe scanning for optical phase measurement, Opt. Commun. , 51, 68/70 (1984). [Non-patent document 7] K. H. Womack: Interferometric phase measurement using spatial synchronous detection, Opt. Eng., 23, 391/395 (1984). [Non-patent document 8] J. Kato et al.: Video-rate fringe analyzer based on phase-shifting electronic moire patterns, Appl. Opt., 36, 8403/8412 (1997). [Non-patent document 9] M. Sugiyama, H. Ogawa, K. Kitagawa and K. Suzuki: Single-shot surface profiling by local model fitting, Appl. Opt., 45, 7999/8005 (2006). [Non-patent document 10] Masaru Sugiyama, Takuya Matsuzaka, Eimitsu Ogawa, Katsuichi Kitagawa, Kazuyoshi Suzuki: One-shot shape measurement method for surfaces with steep step differences, Proceedings of the 2007 Spring Meeting of the Society for Precision Engineering, 585/586 (2007). [Non-patent document 11] Fengzhao Dai, Feng Tang, Xiangzhao Wang, Osami Sasaki, and Peng Feng, "Modal wavefront reconstruction based on Zernike polynomials for lateral shearing interferometry: comparisons of existing algorithms," Appl. Opt. 51, 5028-5037 (2012)

[The problem the invention is trying to solve]

However, the above device has problems such as accuracy, inefficiency of adjustment, and cost of the device, as will be discussed later.

For example, in a Shack-Hartmann sensor, since the light is observed with the aberration of the lens array itself, the accuracy of the lens array directly affects the measurement accuracy. The aberration measurement accuracy of general commercial devices is about 30mλ to 100mλ.

Furthermore, conventional interferometers generally have the problem of requiring a complicated optical system in order to obtain reference light.

In the case of conventional shearing interferometers, although the deviation from a "plane wave or spherical wave" is measured in principle, there is a problem that non-plane waves with large aberrations cannot be measured because the reflected light does not return. As with the other interferometers mentioned above, there is also the problem of overlapping aberrations of optical elements such as mirrors and beam splitters.

In the shearing interferometer, the difference between the two wavefronts, i.e., the shear aberration, is observed. Therefore, in order to obtain the original wavefront of the two wavefronts (original wavefront), it is necessary to observe and analyze the shear direction (the deviation direction of the light split into two) in at least two directions.

However, in the observation of such interference wavefronts in multiple shear directions, errors occur in the observed quantity due to minute vibrations of the device or changes in the optical axis adjustment of the optical element at each observation, making high-precision measurement difficult.

Therefore, the present invention is completed to solve the above-mentioned problem, and its purpose is to provide a shearing interferometry measurement method and a shearing interferometry measurement device that can perform a single measurement of interference wavefronts that were previously performed multiple times in order to efficiently measure the aberration of an optical element. [Means for solving the problem]

In order to solve the above-mentioned problem, the present invention provides a shearing interference measurement method, in which a light beam is split between a light source and a measurement object, and the split light beam is irradiated onto the measurement object to cause interference in a shearing interferometer, and the splitting is performed by an aperture plate arranged between the light source and the measurement object; in the aperture plate, three or more apertures that are not in a straight line are set.

Furthermore, the above-mentioned problem can be solved more effectively by the following method. The aperture plate has a diameter of apertures having the effect of a spatial filter relative to the number of openings of the measurement object facing the measurement object side and the wavelength of the light source. Alternatively, by defocusing the optical system from the light source to form a light-collecting surface, the above-mentioned three or more apertures are collected on the above-mentioned light-collecting surface, thereby evenly improving the illumination of the output light from the aperture plate. Alternatively, the aperture plate is formed of a metal film with a thickness of less than 200 μm, the interval w of the apertures is between more than 10 μm and less than 500 μm, and the diameter d of the apertures is less than 10 μm. Alternatively, the aforementioned apertures are three and are arranged at the vertices of an imaginary equilateral triangle, and the interval w of the aforementioned apertures, when the wavelength of the light source is set to λ, the number of openings of the output light is set to NA _out , and the number of points of the diameter of the circle obtained along the observation screen of the shearing interference point pattern obtained by the image sensor serving as the imaging device is set to n, is set to the size of Formula 2: Formula 2 w=nλ/NA _out (20＜n＜200).

Furthermore, the above-mentioned problem is solved more effectively by the following. The image intensity f(x,y) at the position (x,y) of the shearing interference point pattern image obtained by the above-mentioned interference is subjected to calculation processing to separate the unidirectional independent shearing interference pattern components caused by the combination of two pores constituting the above-mentioned three or more pores. Alternatively, the above-mentioned calculation processing is any one of the methods of 2D Fourier transform, morphological calculation, unidirectional image reduction and blurring, or curve fitting. Alternatively, the above-mentioned calculation processing is 2D Fourier transform, and the spectral distribution after the above-mentioned separation is obtained by formula 4: Formula 4　　G(X,Y)=DFT[f(x,y)].

Furthermore, the above problem can be solved more effectively by the following method. Based on the above-mentioned independent shearing interference pattern components in a single direction, calculation processing is performed to calculate the distribution of the complex extracted spectrum in each direction. Alternatively, when a part of the distribution of the spectrum G(X,Y) after the above-mentioned separation is extracted, the distribution of the extracted complex spectrum in each direction is calculated by formula 5: Formula 5 .

Furthermore, the above problem can be solved more effectively by the following method. In order to analyze the shear aberration distribution, the aberration distribution is calculated based on the extracted complex spectra in each direction by calculation. Alternatively, the calculation is any one of the phase conversion method, Fourier conversion method, spatial phase synchronization method, and local model fitting method. Alternatively, the aberration distribution is calculated by equation 6: .

Furthermore, the above problem can be solved more effectively by the following method. The aberration distribution φ _i (x, y) obtained by the above formula 6 is expanded with a finite Zernike coefficient, and the coefficient is used as an index of the aberration amount of the vector. Alternatively, the shear amount caused by the light from the three apertures and the original aberration coefficient are simultaneously calculated from the Zernike coefficient of the shear aberration obtained by the above index (shear aberration coefficient) by formula 8: Formula 8 .

Furthermore, the above problem can be solved more effectively by the following method. Based on the shear aberration coefficient obtained by the above index, the aberration coefficient (original aberration coefficient) with respect to the outgoing wavefront of the light from the three apertures is calculated based on the relationship of Formula 9: Formula 9 .

Furthermore, the above-mentioned problem is solved more effectively by: Based on the shear aberration coefficient or the original aberration coefficient measured by the above-mentioned interference, it is determined whether the optical axis of the above-mentioned measurement object is tilted from the center of the optical axis and the vertical axis of the above-mentioned aperture plate, and the position and posture of the above-mentioned measurement object are adjusted.

In order to solve the above-mentioned problem, the present invention provides a shearing interference measurement device, which is a shearing interferometer that performs wave splitting of a light beam between a light source and a measurement object lens, and irradiates the aforementioned wave split light beam to the aforementioned measurement object lens to cause interference. The aforementioned wave splitting is performed by an aperture plate arranged between the aforementioned light source and the aforementioned measurement object lens; in the aforementioned aperture plate, more than three apertures that are not in a straight line are set.

Furthermore, the above-mentioned problem can be solved more effectively by the following method. The aperture plate has a diameter of apertures having the effect of a spatial filter relative to the number of openings of the measurement object facing the measurement object side and the wavelength of the light source. Alternatively, by defocusing the optical system from the light source to form a light-collecting surface, the above-mentioned three or more apertures are collected on the above-mentioned light-collecting surface, thereby evenly improving the illumination of the output light from the aperture plate. Alternatively, the aperture plate is formed of a metal film with a thickness of less than 200 μm, the interval w of the apertures is between more than 10 μm and less than 500 μm, and the diameter d of the apertures is less than 10 μm. Alternatively, the diameter d of the aperture is set to the magnitude of Formula 1 when the number of incident openings from the aperture plate to the measurement object is set to NA _in : Formula 1 d[μm]=αλ/ .

Furthermore, the above-mentioned problem can be solved more effectively as follows. The aforementioned apertures are three in number and are provided at the vertices of an imaginary equilateral triangle. The interval w of the aforementioned apertures is set to be the size of Formula 2 when the wavelength of the light source is set to λ, the number of apertures of the output light is set to NA _out , and the number of lines of the image obtained by the image sensor of the camera device (the number of points on the diameter of the circle obtained as the observation screen of the shearing interference point pattern) is set to n: Formula 2 w=nλ/NA _out (50＜n＜100).

Furthermore, the above-mentioned problem can be solved more effectively by the following method. The image intensity f(x, y) at the position (x, y) of the shearing interference dot pattern image obtained by the aforementioned interference is subjected to calculation processing to separate the independent shearing interference fringe components in a single direction caused by the combination of two pores constituting the aforementioned three or more pores. Alternatively, calculation processing is performed based on the aforementioned independent shearing interference fringe components in a single direction to calculate the distribution of the complex extracted spectra in each direction. Alternatively, based on the shearing aberration coefficient or the original aberration coefficient measured by the aforementioned interference, it is determined whether the optical axis of the aforementioned measurement object is tilted from the center of the optical axis and the vertical axis of the aforementioned aperture plate, and the position and posture of the aforementioned measurement object are adjusted. Alternatively, the aforementioned pores are provided at the vertices of an imaginary equilateral triangle, the vertices of an imaginary right triangle, or any of the vertices of an imaginary equilateral triangle. [Effect of the invention]

According to the present invention having the above structure, by splitting the light beam from the light source into three or more apertures and irradiating the measurement object lens, multi-directional shear aberration can be analyzed with a single shot. Therefore, multiple observations required by the previous shearing interferometry method are not required, and errors caused by vibration of the optical system and optical axis adjustment can be reduced.

Furthermore, a new optical system such as an imaging system or a conversion lens for converting a wavefront into a plane wave, which is required in conventional interferometers, is not required. Furthermore, in the present invention, by providing a shear amount evaluation step, observation can be performed even if the optical axes of the two interfering wavefronts are not parallel.

Therefore, the present invention can analyze aberrations with high precision, high efficiency (adjustment, analysis and high speed), and low cost.

In addition, in the technology disclosed in "Non-patent Document 1", although the generation of eddy waves is attempted by using a plurality of holes, it is not like the present invention, and the user of the plurality of holes aperture plate is proposed as a shearing interferometer, and the effect of the present invention cannot be obtained in the shearing interferometer. In addition, in the technology disclosed in "Non-patent Document 2", although the plurality of holes aperture plate is used for the measurement of the wavefront, it is arranged at the rear of the object and the wavefront is measured by focusing on the properties of the eddy waves, which is not like the present invention, and the user of the plurality of holes aperture plate is proposed as a shearing interferometer. Moreover, although the condition that the hole size is large is applied because the amount of light is necessary, it is not like the present invention, and the use of each hole to have the effect of the spatial filter described later is not used, and the effect of the present invention cannot be obtained in the shearing interferometer.

Hereinafter, the shearing interference measurement method and the shearing interference measurement device of the present invention will be described in more detail with reference to the drawings. In addition, some of the following drawings show the outline, and some details are omitted for easy understanding.

The shearing interferometry measuring device of the present invention has, for example, an optical system having a hardware structure schematically shown in FIG. 1 , and implements a unique shearing interferometry measuring method based thereon.

First, the overall outline of the present invention is described.

The present invention basically utilizes the principle of shearing interferometry.

In the present invention, three or more spherical waves that are free of visual aberration are irradiated onto a measurement object, and interference patterns formed by the three or more output lights obtained thereby are analyzed to measure aberration.

Three spherical waves without aberration are generated by irradiating a light source such as a laser to an aperture plate having three holes. At this time, the aperture diameter is determined by the relationship with the lens to be measured using the concept of spatial filters, and spherical waves without visual aberration can be obtained. At this time, in order to obtain spherical waves without visual aberration, it is desirable to reduce the aperture diameter, but since the output light intensity will decrease, it is necessary to collect the light irradiated from the light source to the aperture.

By making the three or more holes formed in the aperture plate not in a straight line, the imaging unit (e.g., image sensor) can obtain shearing interference patterns in two or more directions. Although interference fringes are used in the aberration analysis caused by general interferometry, the present invention does not analyze fringes, but analyzes shearing interference point patterns containing information in multiple directions. Therefore, the present invention can obtain shearing aberrations in multiple directions with one observation.

In order to analyze multi-directional shear aberration, a step is provided to separate the shear interference dot pattern into independent shear interference fringes in a single direction.

In the step of separating into unidirectional independent shearing interference fringes, an example of applying two-dimensional Fourier transform is shown, but the present invention is not limited to this, and the method described later without using two-dimensional Fourier transform can also perform separation.

Next, the shear aberration distribution is obtained from the shear interference pattern in one direction using the spatial Fourier transform method or the like. In addition, the shear aberration distribution is the distribution of the difference between the combinations of the wavefronts of two light waves selected from the three output light waves. In this embodiment, since there are three output light waves, the shear aberration distribution exists with respect to three types of combinations. The aberration of the output wavefront itself relative to the shear aberration is called the original aberration. The original aberration and the shear aberration become distributions on the pupil with units of length. The standard of the unit of length may be set to the wavelength λ or to micrometers or nanometers. The standard of the aberration is generally set to the difference relative to a perfect plane wave, a spherical wave or the ideal design value of the optical system.

In the field of optics, the Zenith coefficient, which is generally used to evaluate aberration distribution, is calculated from the aberration distribution.

From the shear aberration distribution, for example, the original wavefronts of the three respective output lights are reconstructed.

In this step, a shearing amount (amount of deviation of the optical axis center of each light) is necessary.

In the conventional shearing interferometry method, the shearing amount is known from information on design values such as the thickness of the plate causing shearing, but in this method, it is unknown because any optical system can be used as a measurement object.

Therefore, in the present invention, a step of identifying the shear amount from the shear aberration distribution is provided.

Next, a structural example of the shearing interference measuring device of the present invention will be described with reference to FIG. 1 and the like.

FIG. 1 shows an example of the hardware structure of the shearing interference measuring device of the present invention.

Basically, as shown in FIG. 1 , the device of the present invention comprises a light source 100, an aperture plate (also referred to as a photomask) 110 formed with a plurality of holes H (apertures) and held on a first stage 110S, a measurement object lens 130 held on a second stage 130S, an imaging device 150 held on a third stage 150S, and an analyzing unit 170 (not shown) connected to the imaging device 150.

The structure of the light source 100 is not particularly limited. For example, monochromatic light such as semiconductor laser is used, and the light beam from the light source 100 is collected to the aperture provided in the mask 110 .

In addition, the light beams are evenly irradiated with sufficient brightness to the plurality of holes H provided in the mask 110, so that the contrast of the interference image generated in the imaging device 150 is better improved.

Therefore, for example, when the radius of the circumscribed circle surrounding the three apertures is R3, effective light collection can be achieved by setting R3≈αλ/NA _o , where NA _o is the number of openings of the light beam from the light source to the aperture plate, and α is a constant of 1 to 2.

Furthermore, if the aperture plate is completely set at the focal plane, the light intensity at the center without holes will be the highest, wasting the energy of the largest part of the light. To improve this, the aperture plate is defocused as shown below, so that light can be efficiently irradiated to the holes.

Therefore, depending on the wavelength of the light source 100, the multiple holes H can be set in a manner such that they are within the Airy disk of the focal point, or such that a circular or elliptical ring of a high light intensity area formed when the optical system from the light source 100 is defocused is irradiated to the multiple holes H (for example, 3 holes) as shown in FIG. 2 .

FIG2 is an image of an example of focusing the light beam from the light source 100 at the positions of the three apertures as described above, showing an example of obtaining the illumination of the light mask surface by deviating (defocusing) the focal position of the light beam from the light source 100 as shown in FIG2(A), FIG2(B), and FIG2(C).

Therefore, as shown in FIG2(B), by defocusing the optical system from the light source 100, for example, forming a ring-shaped light-collecting surface, and placing three holes (A, B, and C in the figure) on the ring, the illumination of the light beams reaching each hole can be made equal (or sufficiently close to being equal) and improved.

In addition, when defocusing is performed, the defocused irradiation light does not necessarily have to form a completely ring-shaped intensity distribution. If the defocused light does not completely form a ring-shaped area, it is still possible to irradiate the light efficiently to a certain extent.

Furthermore, at this time, the relationship between the light source 100 and the light-collecting lens of the optical system for collecting light may be fixed in advance, and the light-collecting position may be adjusted by adjusting the stage 1 (first stage 110S).

Next, the photomask 110 is a plate (aperture plate) provided with a plurality of holes H (apertures).

In a general shearing interferometer, a diffraction grating and a beam splitter are provided to split the path of the light beam.

However, in the present invention, a mask 110 is disposed on the path from the light source 100 to the measurement object lens 130 to split the light beam, and a shearing interference point pattern containing information of multiple directional components is obtained through interference of the split light beams.

Therefore, the arrangement of the holes H should be such that components in various directions constituting the holes can be extracted from the shear interference point pattern and analyzed. As shown in FIG. 3 , the number of holes should be at least 3 or more, and they should not be in a straight line.

FIG3 is a diagram showing the outline of multiple pores H. FIG3(A) is an example of providing pores H at the vertices (A, B, C) of an imaginary equilateral triangle. FIG3(B) is an example of providing pores H at the vertices (D, E, F) of an imaginary right triangle. FIG3(C) is an example of providing pores H at the vertices (H, I, J) of an imaginary equilateral triangle and its centroid (G).

For example, when the aperture H is arranged as shown in FIG3(A), interference patterns are formed between the apertures A and B, interference patterns are formed between the apertures B and C, and interference patterns are formed between the apertures A and C. For example, from the relationship between the two apertures, the shearing deviation of the light beam in two directions as shown in FIG4(A) can be observed. FIG4(A) is an example of a two-direction deviation; FIG4(B) is an example of a three-direction deviation. In the same FIG4, RF2 represents the repeated area in the case of a two-direction deviation; RF3 represents the repeated area in the case of a two-direction deviation. In the present invention, as shown in FIG4(B) or FIG1(B), the light beams deflected in three directions are synthesized, and in the imaging device 150, a shearing interference point pattern can be obtained in the area of RF3.

Such a plurality of pores can be formed, for example, by forming a photoresist (metal evaporation film (metal film)) on a glass plate using a photolithography technique such as sputtering as shown in FIG3(D). Then, when the pores are formed on the glass plate in this way, the glass plate side is arranged toward the light source 100 side. However, it is also possible to form pores in a metal film by perforating without using such a glass plate by etching or the like.

Metal films can utilize gold, chromium, silver, copper, etc.

The thickness of the metal film is preferably 0.1 μm or more and 200 μm or less. When making pores by micro-photoetching technology, a thinner metal film is better from the perspective of sputtering cost and etching process. However, if the thickness of the film is too thin, light will pass through, that is, there is a problem that the light cannot be completely blocked. The thicker the film, the more difficult it is to accurately form a hole of the order of 1 μm in diameter.

When a metal film having multiple holes on a glass plate is used as an aperture plate, the glass plate is arranged on the light source side to prevent the aberration of the glass from being mixed in, and the metal film is arranged on the output light side, and the aberration of the glass is eliminated by the effect of the spatial filter of the aperture. In addition, the aperture diameter d [μm] of the aperture of such multiple holes is determined by the following formula 1 based on the view of a spatial filter (spatial frequency filter) that clears the wavefront, and is related to the measurement object lens 130 arranged on the side of the camera device 150 from the mask, as shown in FIG. 5 (A). (Refer to "Note A" below) Formula 1: Aperture diameter d = αλf/D = αλ/NA _in .

The symbols in Formula 1, as shown in FIG5(A), represent the following respectively: λ = oscillation wavelength of laser (μm) f = distance from the measurement object lens 130 (mm) D = diameter of the measurement object lens 130 (mm) α = a constant between 1.0 and 2.0, and NA _in is the number of openings on the incident side of the object to be measured.

In addition, regarding the aperture number (NA), the optical system of the present invention has three, as shown in FIG5(B), the aperture number of the light beam from the light source to the aperture plate is set to _NA0 , the incident aperture number from the aperture plate to the measurement object is set to _NAin , and the output light aperture number from the measurement object to the camera (imaging device) is _NAout .

Based on Formula 1, if the NA _in of a general imaging lens is about 0.05 to 0.5, then d is in the practical range of 0.5 μm or more and 50 μm or less.

Here, α is the diameter of the Airy ring, which is 1.27. As α is smaller, light with less aberration can be generated, and as α is increased, the amount of light can be increased.

Next, the distance between the apertures of this diameter is determined by the degree to which 20 to 200 lines (or synthetic dot patterns) are generated on the image sensor of the imaging device 150. The resolution is reduced if there are less than 20 lines, and it takes time to analyze and calculate if there are more than 200 lines.

Therefore, for example, assuming that the wavelength of the light source 100 is λ, the number of apertures for output light is NA _out , and the interval between the apertures is w, the number of lines (or the number of points along the diameter of the circular image obtained as a shearing interference point pattern) n is expressed by the following formula 2. Formula 2

For example, when the number of lines is set to 50, NA _out = 0.1, and the wavelength is 0.66μm, the interval between holes becomes the secondary formula. =50*0.66/0.1=330

Compared with general optical systems such as smartphone camera lenses, the interval between holes is selected from 10μm to 500μm to obtain an appropriate number of lines. In addition, the aperture number NA _out of the output light is the ratio of the focal length seen from the image on the image sensor to the radius of the pupil image on the image sensor.

In this way, the photomask 110 provided with the plurality of holes H is held by the first stage 110S, and the position and posture of the photomask 110 are controlled by the first stage 110S.

That is, the first stage 110S is basically formed of the same structure as the second stage and the third stage described later, and for example, the position and posture can be adjusted using an angle measuring stage.

Next, the angle measuring stage is a support stage with 6-axis degrees of freedom, which can move in the positive/negative direction of each axis of x, y, and z, and rotate in the clockwise and counterclockwise directions of each axis (tilt adjustment) within a predetermined range.

Furthermore, the adjustment of the first to third stages may be performed manually while observing the image obtained by the imaging unit 155 of the imaging device 150 and the analyzed image. For example, as shown in FIG. 6 , the control device 165 connected to the imaging device 150 and the analyzing unit 170 may be used to perform adjustments based on the image of the display device 160 connected to the control device 165.

Among them, FIG6 is a block diagram showing an analysis unit 170 of the measuring device of the present invention. In the present invention, as shown by the solid line in FIG6, the image acquired by the camera 150 is processed by the analysis unit 170 of the control device 165, and the data processed by the analysis unit 170 is output by the display device 160, and all of these are controlled by the control device 165. Therefore, the user can observe the output image of the display device 160 and adjust and configure each stage manually.

Furthermore, if necessary, as shown by dotted lines in FIG. 6 , a driving unit (113, 133, 153) is provided on each of the first to third carriers, and each driving unit is controlled by a control device 165. The control from the control device 165 side in conjunction with the analysis results is also possible.

Next, the measurement object lens 130 is a measurement object lens of aberration, and is disposed between the above-mentioned mask 110 and the imaging device 150. Next, in the shearing interferometer of the present invention, since no redundant optical system is provided between the mask 110 and the measurement object lens 130, or between the measurement object lens 130 and the imaging device 150, errors caused by redundant optical systems do not overlap, and the aberration of the measurement object lens 130 can be measured with high efficiency and high precision.

Furthermore, the measurement object lens 130 is held by a second stage 130S having six-axis degrees of freedom, and the position and posture of the measurement object lens 130 can be adjusted by the second stage 130S.

Next, the distance between the measurement object lens 130 and the mask 110 is adjusted by the second stage 130S based on the concept of the above-mentioned "Note A".

Furthermore, the adjustment of the optical axis (position and posture) of the measurement object lens 130 and the mask is also performed by the second stage 130S. However, as described later, no detailed adjustment is performed from the initial measurement. The shear aberration can be calculated from the point pattern obtained by the imaging unit 155, and the position and posture of the optical axis can be calculated based on the result, thereby adjusting the optical axis to the optimal position to obtain the aberration result.

That is, in the present invention, the image information formed by the camera 150 is measured by the analysis unit 170 through the light beam from the light source 100, the mask 110 and the measurement object lens 130, and the optical axis of the measurement object lens 130 and the mask is adjusted according to the result, so that only the aberration when the optical axis is optimal can be adopted as the result.

Next, the imaging device 150 is a device having an imaging unit 155 composed of an image sensor, etc., and is a device that uses the light beam from the light source 100 to capture the shearing interference dot pattern formed by the mask 110 and the measurement object lens 130.

Next, the imaging device 150 is supported by the third stage 150S having six-axis degrees of freedom.

Therefore, the imaging device 150 is adjusted by the third stage 150S based on the position of the measuring lens as described above, in such a manner that the plane formed by the imaging unit such as the image sensor is parallel to the plane perpendicular to the principal point of the measuring object lens 130, and in such a manner that the optical axis of the measuring object lens 130 passes through the center of the imaging unit 155.

Next, the distance between the imaging unit 155 and the measuring object lens 130 is adjusted so that the outer edge of the shearing interference dot pattern formed by three images created by the light beam from the exit pupil of the measuring object lens is within the imaging element such as the image sensor constituting the imaging unit.

Furthermore, the camera 150 is connected to an analysis unit 170 (not shown). The analysis unit 170 is connected to a display unit (display device) 160 as shown in FIG. 6 , and analyzes the shearing interference point pattern photographed by the camera 150 .

Therefore, the analysis unit 170, as described later, has at least a calculation structure capable of processing the extraction step of information of each unidirectional shearing pattern, the shearing interference pattern analysis step, the Zernike coefficient calculation step, the original aberration reconstruction step, and the like.

Furthermore, in order to further improve the accuracy, a structure capable of handling a shear amount identification step and an optical axis position and posture calculation step is also suitably incorporated.

Next, the analysis process according to the present invention and the specific analysis method performed by the analysis unit 170 are described.

FIG. 7 is a flow chart showing an example of the flow of analysis.

In the present invention, the relative relationship between the mask 110 and the camera (imaging element 155) is first calibrated in advance (step S1). Then, the mask 110 and the camera are adjusted in a state where the measurement object lens 130 is removed from the device in such a way that the plane formed by the mask 110 and the plane formed by the imaging element become parallel.

Fig. 8 is an example of a shear pattern observed in the state where the measuring object lens 130 is removed from the present device. In the present invention, the shear aberration in the state without the measuring object lens 130 is analyzed in this way, and the positional relationship between the mask and the image sensor is constructed based on the shear aberration.

Next, the position/posture of the object lens is adjusted (step S2). In the present invention, since the shear aberration changes according to the position/posture, it is necessary to master it. The position and posture mastery, as described above, does not necessarily have to be correct from the beginning of measurement. In the present invention, the result is calculated from the shear aberration feedback caused by the later step S8 and adjusted.

Next, the light source 100 irradiates the light mask 110, and the image sensor 150 observes the output light from the measurement object lens 130 (step S3). In the present invention, the output light forms a shearing interference point pattern, and the observed output light becomes, for example, as shown in FIG. 9 or FIG. 10. Among them, FIG. 9 shows that the measurement object lens 130 is a plano-convex lens, and FIG. 10 shows an example of a lens for a camera for a smartphone.

Next, after obtaining the clipping interference point pattern, a two-dimensional analysis area is extracted from the observed image (step S4). The two-dimensional analysis area is extracted, for example, as shown in the repeated area RF3 of FIG. 4(B), and a portion including information from each hole portion provided in the mask is selected.

After the analysis area is extracted, the shear interference pattern in each single direction is separated (step S5), and the interference patterns in each of the three directions are analyzed to calculate the wavefront (phase) from the interference patterns (step S6).

Next, the calculated three-directional shear aberrations are expanded using Zenkie polynomials to calculate Zenkie coefficients (step S7).

Furthermore, the posture, position, etc. of the object are calculated from the shearing aberration calculated as described above (step S8), and the shearing amount is calculated from the shearing aberration (step S9).

Next, a procedure of calculating the original aberration from the shearing aberration and the shearing amount (step S10) is performed. However, steps S5 to S10 will be described in detail below with reference to an analysis example.

Analysis Example Figure 11 is an example of a flow chart for obtaining the original aberration coefficient Co from the cut point pattern image using the observed simulated image of the spherical lens shown in Figure 12.

First, set the image intensity of each point position x,y of the cut point pattern image to the following formula 3. Formula 3　　f(x,y)

The diameter of the ball lens is 8 mm, the light source 100 is set at a position 10 mm away from the center of the ball lens, and the camera is adjusted to be 30 mm away from the light source 100. Also, assume that three apertures are arranged in an equilateral triangle.

As shown in the flowchart of FIG11 , the shear spectrum in each single direction is first extracted (step (a)).

Specifically, in order to separate the shear interference fringes in three directions into three directions, for example, the 2D Fourier transform of Equation 4 is applied. Equation 4　　G(X,Y)=DFT[f(x,y)]

Among them, X, Y are the spatial frequencies in the image space after Fourier transformation. The distribution of the spectrum G(X,Y) after Fourier transformation of the observed image is shown in Figure 13. In addition, although the spectrum is complex, its absolute value intensity is shown in the figure.

The calculation of spectral distribution can be applied using DFT Discrete Fourier Transform, Discrete Cosine Transform or FFT Fast Fourier Transform.

From the figure, it is possible to identify the characteristic pattern that appears in every 60-degree direction. The pattern in each direction is extracted with a window width of 32Hz, with the position far away from the center position at 35Hz as the center. The unit Hz represents the wave number 35 waves relative to the observation aperture diameter.

The window width is determined by how high the spatial frequency is included in the aberration distribution. In the case of optical elements such as ordinary lenses, the distribution of the emitted light waves when irradiated with spherical waves is smooth, so even with a high window width of about 50 Hz, wavefront information can be extracted.

In order to extract the distribution of the absolute values of the extracted complex spectra G_i(X,Y) in the directions of -90 degrees, 30 degrees, and 150 degrees, the calculation of the following formula 5 is performed to obtain each extracted complex spectrum. The extraction result is shown in the extracted spectrum image of Figure 14. Formula 5 .

The added character i indicates the corresponding three shearing directions. For example, if it is the shearing between beam 1 and beam 2, i=(12), if it is the shearing between beam 2 and beam 3, i=(23), and if it is the shearing between beam 3 and beam 1, i=(31). _Xi , _Yi represent the center of each shearing spectrum pattern. is a window function with a value of 0 or 1. Here, a square window with a window width of 32 Hz (relative to the wave number of the observation aperture diameter 32) is applied.

In addition, although the above description is about the method of separating into independent shearing interference fringe components in a single direction using Fourier transform, as exemplified in the following (1) to (3), there are other methods of separating into several independent shearing interference fringe components in a single direction.

(1) "Morphological calculation-based separation method": A morphological calculation-based expansion process is applied in the direction perpendicular to the three shear directions of interest. This process combines the shear direction of interest with the points in the perpendicular direction. After this process, a contraction process is applied to obtain a texture pattern. By performing this process independently for each shear direction, it is possible to separate the shear interference pattern components into independent unidirectional components.

(2) "Image separation by unidirectional reduction and blur processing": When an observation image of a shearing interference dot pattern as shown in FIG. 16(A) is obtained, the entire observation image is reduced in a direction perpendicular to the shearing direction of interest by image processing, for example, as shown in FIG. 16(B). Then, by applying blur processing, independent dots can be combined to form a pattern. By performing this processing independently of the shearing direction, it is possible to separate the shearing interference pattern components in a single direction.

(3) "Method by curve fitting": As shown in FIG16(C), the peak coordinates of the dot pattern are fitted with a smooth parametric curve. The curve obtained by fitting itself becomes the texture pattern. Although polynomial functions are representative of parametric curves, any function that can be used for regression curves can be used.

Next, the shear aberration distribution is calculated by the interference pattern analysis method (step (b)). Specifically, by using equation 6, each extracted complex spectrum is subjected to an inverse Fourier transform IDFT in real space to calculate the phase angle of the complex amplitude. The calculated distribution of shear aberration in the 90-degree direction is shown in Figure 15. Equation 6 .

In the case of large aberrations, since the phase angle calculated above exceeds the range of [-π　π], the phase unwrapping method is applied to obtain a gapless continuous phase distribution.

Next, the series expansion coefficient (Zehnike coefficient) is calculated (step (c)).

In the field of optics, the aberration distribution is expressed by the Zenkir polynomial, which is very compatible with optical systems with round pupils such as lenses. That is, the aberration distribution φ _i (x, y) obtained by the above formula 6 is expanded with a finite Zenkir coefficient, and the coefficient vector is used as an index of the aberration amount. In addition, the additional characters i=12,23,31 are additional characters representing the three shearing directions. In the following, the additional characters are omitted because the same processing is performed in each direction.

Since the aberration distribution φ(x,y) is data obtained discretely at each pixel about x,y, the coefficients can be obtained by the least square method using the basis vector sampled at the pixel position corresponding to the basis function of the Zernike polynomial. That is, the least square solution of the equation of equation 7 can be obtained by linear calculation. Equation 7　　{φ}=[Z]{c}

Among them, {φ} is a vector of the aberration obtained by discrete distribution arranged in the longitudinal direction, and [Z] is a Zenith basis matrix in which the terms of the discretely sampled Zenith basis column vector are arranged in the column direction. {c} is a Zenith coefficient vector. In this analysis example, 16 terms of the Zenith coefficient of the stripe arrangement are calculated. The obtained Zenith coefficient of the shear aberration (shear aberration coefficient) is shown in Figures 17(A) and (B). In addition, Figure 17(B) is an enlarged version of a portion of Figure 17(A). In addition, the initial constant term _Z0 of the Zenith coefficient is not shown in the figure.

Next, the position/orientation is calculated (step (d)), and based on the result, the position and orientation of the lens to be measured are adjusted.

That is, in the above step (c), after calculating the shear aberration coefficient cs _, the aberration of the wavefront of the light from the three holes is obtained, and the center of the optical axis can be calculated by searching for the position where the coma component or astigmatism component from the three holes of _cs becomes the minimum. In addition, the slope of the optical axis can be calculated from the difference between the three defocus components.

The slope of the optical axis is the slope of the axis of the lens to be measured with the normal direction of the aperture plate as a reference.

Next, the shear amount is determined (step (e)).

The amount of deviation between the three image sensors of the emitted light is called shearing. Shearing is necessary information to obtain the original aberration.

Generally speaking, if the design value and measurement conditions of the optical element are obtained, for example, as shown in Figure 18, the light source 100 (not shown), the image sensor 150, the position and posture of the optical element 130, etc. are used to implement light tracking simulation. Although the shear amount can be calculated numerically, the shear amount is calculated by other methods because this is not possible in the present invention.

Therefore, it is also a feature of the present invention to identify the shear amount from the shear aberration.

The simplest method is to calculate the shearing amount from the deviation of the edge of the opening of the optical element as shown by the highlighted arrows in Figure 19. In this case, the shearing amount is extracted from the aperture edge of the shearing pattern image. More specifically, the shearing amount can be calculated by measuring the width of the portion between the front ends of the two arrows in Figure 19 and comparing it with the "outer circumference of the pupil" obtained from the image.

On the other hand, although the method described in the above shear amount identification step is simple, the obtained image may have unclear edges and thus cause errors.

Therefore, in order to identify higher shear amounts, there is a method of constructing an observation equation that uses the original wavefront and shear amount as design variables to make the inappropriate problem appropriate for analysis.

In the following analysis example, the shearing amount is identified from the shearing aberration coefficient. That is, the shearing amount _si and the original aberration coefficient co are used as design variables to regress the optimization problem of minimizing the evaluation function of equation 8, and the shearing amount and the original aberration coefficient are calculated simultaneously. .

Wherein, c _skl represents the shear aberration coefficient between beams k and l. Also, [Z] is a Zenith basis matrix that arranges the terms of the discretely sampled Zenith basis column vectors in the column direction. The Zernike basis matrix is obtained by parallel translation of the pupil unit circle using the shear vector as the parallel translation amount. Formula 8 is an example of a target function that minimizes the shear aberration, the original aberration, and the squared residual of the shearing amount. However, if the L1 standard is used in addition to the square standard, there is also a target function that evaluates the residual through a monotonic function such as a logarithmic function, and the same result is obtained.

In addition, since the residual terms on the right side of equation 8 contain mutually dependent residual terms, it is also possible to solve the simultaneous equations by omitting the dependent residual terms. In addition, since this optimization problem is a bad condition, it is better to apply the adaptation method commonly used in inverse analysis in order to explore s_i, c_o. For example, the weighted residual method, the unknown number reduction method, Tikhonov's adaptation method, the MAP method, etc. can be applied to achieve the stabilization of the solution.

Next, the original aberration is reconstructed to calculate the aberration of each light (hereinafter referred to as the original aberration) from the shear aberration. (Step (f)) In the analysis of the original aberration, the shear amount (the deviation amount of the two wavefronts) is necessary, and it can be known in advance from the thickness and refractive index of the plate that generates the shear light from the previous method. In this method, since the shear amount is unknown due to the influence of the measured object, the shear amount is calculated using the method shown in the above step e.

The analysis of the original aberration is specifically performed as follows.

Based on the shear aberration coefficient obtained in step c above, the aberration coefficient (original aberration coefficient) for the outgoing wavefront of the light from each aperture is calculated. Let the shear vector be s_i, then the shear aberration coefficient _cs and the original aberration coefficient co are related by equation 9: .

In the above formula, [Z] is the Zenkirche basis matrix that arranges the terms of the discretely sampled Zenkirche basis column vectors in the column direction. The shear matrix is obtained by parallel translation of the pupil unit circle using the shear vector as the parallel translation amount. Here, (k, l) = (1, 2), (2, 3), (3, 1). For the calculation of the shear matrix, refer to "Non-patent Document 11" and the like. In the above formula, because and The quantities of are known, and the original aberration coefficient c _o can be obtained by solving the equation by the least square method or the weighted least square method. In addition, since the simultaneous equations in equation 9 include mutually dependent equations, it is also possible to solve the simultaneous equations by omitting the dependent equations as appropriate.

Therefore, through the above calculation processing, for example, the original aberration coefficient shown in Figure 20 can be obtained.

In addition, the order of each step in the flowchart of FIG. 11 is not limited to this, unless the result of the previous step is used. Therefore, for example, the position/attitude calculation step (step (d)) is appropriately fed back to step (a), and the position/attitude is adjusted based on the result. Furthermore, in the original aberration reconstruction step (step (f)) based on the shear aberration coefficient, the shear amount is determined from the shear amount determination step (step (e)), and the original aberration is reconstructed.

Therefore, through the above steps, according to the shearing interferometer measurement method and shearing interferometer measurement device of the present invention, the original aberration, etc. can be obtained.

Therefore, according to the shearing interferometry measurement method and shearing interferometry measurement device of the present invention, the aberration of the optical element to be measured can be efficiently measured, and when measuring shearing interferometry, the interference wavefront measurement that was previously performed multiple times can be performed in one measurement.

In addition, the above-described example is an example of the measuring method/device of the present invention, and the scope of the intent of the present invention can also adopt different methods.

For example, in the step (step (b)) of calculating the shear aberration distribution by the interference pattern analysis method shown in Figure 11, the phase conversion method (non-patent document 3, non-patent document 4), the Fourier transformation method (non-patent document 5), the spatial phase synchronization method (non-patent documents 6 to 8), and the local model fitting method (Local Model Fitting method; LMF method) (non-patent documents 9, 10) are applied to analyze the wavefront from the interference pattern image.

Next, other specific analysis examples are described.

Analysis Example 1 (Aberration measurement without a test object) In order to verify the accuracy of this method, aberration measurement without a test object was performed. The distance between the light source and the camera was set to 33 mm and five measurements were performed. One of the observed images is shown in Figure 21 (A). Figure 21 (B) is an enlarged view of the square frame portion of Figure 21 (A) as in Figure 21. In addition, Figures 22 (A) to (C) show the aberration analysis results. Each figure represents the aberration of light from the aperture in the directions of 150 degrees, 30 degrees, and 270 degrees as a Zenkir coefficient. In addition, the first constant term (stopper component) called z0 among the 16 Zenkir coefficients is omitted. Since the theoretical value can be calculated in the case without a test object, the theoretical value is also shown for comparison of accuracy. It is found that the marks of the 5 measured values overlap with the theoretical values.

Because the defocus component Z3 is large, only the items Z4 to Z16 are expanded on the vertical axis and shown in Figures 23(A) to (C). It is found that the marks of the five measured values overlap with the theoretical values.

The difference from the theoretical value is shown in Figure 24 (A) to (C). The standard deviation for 5 measurements is 0.799mλ, which makes it possible to achieve accuracy that was previously unattainable with low-cost hardware and efficient optical axis adjustment in a short time.

Analysis Example 2 (Measurement of aberration of a plano-convex lens) In order to verify the accuracy of this method, aberration of a plano-convex lens was measured.

The distance between the light source and the camera was set to 33 mm and five measurements were performed.

The plano-convex lens used is SLB-10-80P manufactured by SIGMA Koki Co., Ltd.

One of the observed images is shown in Fig. 25(A). Fig. 25(B) is an enlarged view of the quadrangular frame portion of Fig. 25(A) as in Fig. 25.

The aberration analysis results are shown in Figures 26 (A) to (C). Each figure shows the aberration of light from the apertures in the directions of 150 degrees, 30 degrees, and 270 degrees in the form of Zenick coefficients. In addition, the first constant term (plug component) called z0 among the 16 Zenick coefficients is omitted. It is found that the marks of the five measured values overlap with good reproducibility.

Because the defocus component Z3 is large, only the items Z4 to Z16 are expanded on the vertical axis and shown in Figures 27 (A) to (C). In the expanded graphs, it can be seen that the marks of the five measurement values overlap with good reproducibility.

The difference from the first measurement is shown in Figure 28 (A) to (C). The standard deviation is 0.625 mλ for 5 measurements.

100: Light source 110: Aperture plate (mask) 110S: 1st stage 113: 1st drive unit 130: Measurement target lens 130S: 2nd stage 133: 2nd drive unit 150: Imaging device 150S: 3rd stage 153: 3rd drive unit 155: Imaging unit 160: Display device 165: Control device 170: Analysis unit H: Aperture (hole) d: Aperture diameter w: Aperture interval (distance between apertures) λ: Laser oscillation wavelength f: Distance between measurement target lens and mask D: Diameter of measurement target lens cs: shear aberration coefficient s: shear amount s_i: shear vector Co: original aberration coefficient

[Figure 1] A side view showing an overview of the hardware of the optical system of the example of the present invention. In addition, the repeated circles on the right side are front views schematically showing a light beam offset in three directions. [Figure 2] An image showing an example of focusing the light beam from the light source at the positions of three apertures; Figures 2(A) to 2(C) show the state of sequential defocusing. [Figure 3] A front view showing an example of apertures with multiple holes. [Figure 4] A front view showing an example of shear offset of the light beam; Figure 4(A) shows an example of offset in two directions; Figure 4(B) shows an example of offset in three directions. [Figure 5] Figure 5(A) is a side view showing an example of a spatial filter of the example of the present invention; Figure 5(B) is a side view showing the number of openings of the example of the present invention along the example of Figure 1. [Fig. 6] is a block diagram showing an analysis unit of a measuring device according to the present invention. [Fig. 7] is a flowchart showing an example of the analysis process. [Fig. 8] is an image showing an example of a shearing pattern observed without a test object. [Fig. 9] is an image showing an example of a shearing pattern observed (plano-convex lens). [Fig. 10] is a front view of an image showing an example of a shearing pattern observed (smartphone camera lens). [Fig. 11] is a flowchart showing the sequence from the distribution of interference fringe intensity to the acquisition of the original aberration coefficient. [Fig. 12] is an example of a simulated image observed with a spherical lens. [Figure 13] The full spectrum image obtained by Fourier transforming the observed simulation image of the ball lens, with the horizontal and vertical axes representing the spatial frequency 1/(pixcel). [Figure 14] The extracted spectrum images in each direction of the wavefront information extracted with a window width of about 50 Hz. [Figure 15] The image showing the shear aberration distribution in the 90-degree direction. [Figure 16] The extracted images of various unidirectional fringe images are shown. [Figure 17] The diagram showing the shear amount of the dot pattern of the interference image. [Figure 18] The oblique view showing an example of the shear amount identified by the ray tracing method. [Figure 19] The diagram showing the measurement part of the case where the shear amount is identified based on the shear interference dot pattern. [Figure 20] The diagram showing the original aberration coefficient. [Figure 21] An example of an observed image when no object to be tested (measurement target) is set. [Figure 22] A diagram showing the aberration analysis results of the situation in Figure 21. [Figure 23] An enlarged diagram of Z4 to Z16 in Figure 22. [Figure 24] A diagram showing the difference from the theoretical value. [Figure 25] An example of an observed image when a plano-convex lens is set as the measurement target. [Figure 26] A diagram showing the aberration analysis results of the situation in Figure 25. [Figure 27] An enlarged diagram of Z4 to Z16 in Figure 26. [Figure 28] A diagram showing the difference from the theoretical value.

100: Light source

110: Aperture plate (light mask)

110S: The first carrier

130: Measurement object lens

130S: The second carrier

150: Camera device

150S: The third carrier

Claims (27)

A shearing interferometer measurement method is to split a light beam between a light source and a measurement object, and irradiate the split light beam to the measurement object to cause interference in a shearing interferometer. The splitting is performed by an aperture plate disposed between the light source and the measurement object; Three or more apertures that are not in a straight line are provided in the aperture plate. A shearing interference measurement method as recited in claim 1, wherein the aperture plate has a diameter of apertures having a spatial filter effect relative to the number of openings of the measurement object facing the measurement object side and the wavelength of the light source. A shearing interference measurement method as described in claim 1, wherein the optical system from the aforementioned light source is defocused to form a light-collecting surface so that the aforementioned three or more apertures are placed on the aforementioned light-collecting surface, thereby evenly improving the illumination of the output light from the aforementioned aperture plate. A shear interference measurement method as described in claim 1, wherein the aperture plate is formed of a metal film having a thickness of less than 200 μm, the interval w of the apertures is between 10 μm and 500 μm, and the diameter d of the apertures is less than 10 μm. A shearing interference measurement method as described in claim 1, wherein the aforementioned apertures are three and are arranged at the vertices of an imaginary equilateral triangle, and the interval w of the aforementioned apertures, when the wavelength of the light source is set to λ, the number of openings of the output light is set to NA _out , and the number of points of the diameter of the circle obtained along the observation screen of the shearing interference point pattern obtained by the image sensor serving as the photographic device is set to n, is set to the size of Formula 2: Formula 2 w=nλ/NA _out (20＜n＜200). A shearing interference measurement method as described in claim 1, wherein the image intensity f(x, y) at the position (x, y) of the shearing interference point pattern image obtained by the aforementioned interference is calculated and processed to separate it into unidirectional independent shearing interference pattern components caused by the combination of two pores constituting the aforementioned three or more pores. A shearing interference measurement method as recited in claim 6, wherein the aforementioned calculation processing is any one of a 2D Fourier transform, a separation method due to morphological calculation, a separation method due to unidirectional image reduction and blurring processing, or a method due to curve fitting. As described in claim 6, the shearing interference measurement method, wherein the aforementioned calculation process is a two-dimensional Fourier transform, and the spectral distribution after the aforementioned separation is obtained by equation 4: Equation 4　　G(X,Y)=DFT[f(x,y)]. A shearing interference measurement method as recited in claim 6, wherein calculation processing is performed based on the independent shearing interference fringe components in the aforementioned single direction to calculate the distribution of the complex extracted spectra in each direction. In the shearing interferometry method of claim 8, when a part of the distribution of the separated spectrum G(X,Y) is extracted, the distribution of the extracted complex spectrum in each direction is calculated by equation 5: A shearing interferometry measurement method as recited in claim 9, wherein, in order to analyze the shear aberration distribution, the aberration distribution is calculated based on the extracted complex spectra in the aforementioned directions through calculation processing. A shearing interferometry measurement method as recited in claim 11, wherein the calculation processing is any one of a phase conversion method, a Fourier conversion method, a spatial phase synchronization method, and a local model fitting method. The shearing interferometry method as recited in claim 11, wherein the aberration distribution is calculated by equation 6: . The shearing interferometry measurement method as recited in claim 13 is characterized in that the aberration distribution φ _i (x, y) obtained by the above-mentioned equation 6 is expanded using finite Zernike coefficients, and the coefficients are used as indices of the aberration amount of the vector. The shearing interferometry method as recited in claim 14, wherein the shearing amount and the original aberration coefficient due to light from three apertures are simultaneously calculated from the shearing aberration coefficient (shearing aberration coefficient) obtained by the aforementioned index by equation 8: . The shearing interferometry measurement method as recited in claim 14, wherein, based on the shearing aberration coefficient obtained by the aforementioned index, the aberration coefficient (raw aberration coefficient) relative to the outgoing wavefront of the light from the three apertures is calculated based on the relationship of equation 9: . A shearing interferometry measurement method as described in any one of claims 1 to 15, wherein, based on the shear aberration coefficient or the original aberration coefficient measured by the aforementioned interference, it is determined whether the optical axis of the aforementioned measurement object is tilted from the center of the optical axis and the vertical axis of the aforementioned aperture plate, and the position and posture of the aforementioned measurement object are adjusted. A shearing interferometer measuring device is a shearing interferometer that splits a light beam between a light source and a measurement object lens, and irradiates the split light beam to the measurement object lens to cause interference. The splitting is performed by an aperture plate disposed between the light source and the measurement object lens; Three or more apertures that are not in a straight line are provided in the aperture plate. A shearing interferometer measuring device as recited in claim 18, wherein the aperture plate has a diameter of apertures having the effect of a spatial filter relative to the number of openings of the measurement object facing the measurement object side and the wavelength of the light source. As described in claim 18, the shearing interference measuring device is configured such that the optical system from the light source is defocused to form a light-collecting surface, so that the three or more apertures are placed on the light-collecting surface, thereby evenly improving the illumination of the output light from the aperture plate. A shear interference measuring device as described in claim 18, wherein the aforementioned aperture plate is formed by a metal film having a thickness of less than 200 μm, the interval w of the aforementioned apertures is between greater than 10 μm and less than 500 μm, and the diameter d of the aforementioned apertures is less than 10 μm. A shearing interferometer measuring device as recited in claim 18, wherein the diameter d of the aperture is set to the magnitude of Formula 1 when the number of incident openings from the aperture plate to the measurement object is set to NA _in : Formula 1 d[μm]=αλ/NA _in . A shearing interference measuring device as described in claim 18, wherein the aforementioned apertures are three and are arranged at the vertices of an imaginary equilateral triangle, and the interval w of the aforementioned apertures, when the wavelength of the light source is set to λ, the number of openings of the output light is set to NA _out , and the number of lines of the image obtained by the image sensor of the imaging device (the number of points on the diameter of the circle obtained as the observation screen of the shearing interference point pattern) is set to n, is set to the size of Formula 2: Formula 2 w=nλ/NA _out (50＜n＜100). A shearing interference measuring device as recited in claim 18, wherein an image intensity f(x, y) at a position (x, y) of a shearing interference dot pattern image obtained by the aforementioned interference is subjected to calculation processing to separate into unidirectional independent shearing interference pattern components caused by a combination of two pores constituting the aforementioned three or more pores. A shearing interference measuring device as recited in claim 24, wherein calculation processing is performed based on the independent shearing interference pattern components in the aforementioned single direction to calculate the distribution of the complex extracted spectra in each direction. A shearing interferometer measuring device as recited in claim 18, wherein, based on the shear aberration coefficient or the original aberration coefficient measured by the aforementioned interference, it is determined whether the optical axis of the aforementioned measurement object is tilted from the center of the optical axis and the vertical axis of the aforementioned aperture plate, and the position and posture of the aforementioned measurement object are adjusted. A shear interference measuring device as recited in any one of claims 18 to 26, wherein the aforementioned pores are located at the vertices of an imaginary equilateral triangle, the vertices of an imaginary right triangle, or any one of the vertices of an imaginary equilateral triangle.

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