JP2003294412A - Holography apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance functionality and general-purpose properties with respect to the measurement of the reproduction of an image or the surface shape of an object to be measured due to holography. <P>SOLUTION: Complex amplitude data comprising the phase data and amplitude data of the reflected light of the object to be measured at a plurality of positions in an optical axis direction is calculated on the basis of interference fringe data obtained by picking up the image of an interference fringe between the reflected light of the object to be measured and reference light. Then, the amplitude data is converted to the real image or virtual image of the object to be measured. At the time of conversion, the center of the image of zero-order diffraction light in the complex amplitude data is adjusted so as to become a predetermined position on a reproduced image (step S21). The distance on the reproduced image of the center of the image of the zero-order diffraction light in the complex amplitude data after adjustment and the center of the real image or virtual image in the complex amplitude data is calculated (step S22), and the real image or virtual image is magnified or contracted on the basis of the center of the real image or virtual image in the complex amplitude data to correct the difference between the position and size of the real image or virtual image, after conversion accompanied by the difference of the position in the optical axis direction (step S23). <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a holographic device.

[0002]

2. Description of the Related Art In digital holography, reflected light when an object is irradiated with light and reference light for interfering with the light are made incident on an image pickup device such as a CCD (Charge Coupled Device) to reflect the reflected light and the reference light. This is a technique for recording the interference fringes generated by the interference with the image sensor, and calculating the complex amplitude of the reflected light by a numerical calculation based on the interference fringe data.

[0003]

The amplitude and phase of a light wave are collectively referred to as complex amplitude. The complex amplitude data of the reflected light at any position in the optical axis direction of the interference optical system, that is, the amplitude data and the phase data can be obtained by calculation.For example, the complex amplitude of the reflected light at the position where the object originally existed can be calculated. When obtained, a two-dimensional object image (amplitude data or intensity data obtained by squaring the amplitude data) and a height (phase data) of the object that are substantially in focus are reproduced.

In the holography, the reference light is diffracted by the hologram that acts as a diffraction grating at the time of reproduction to behave as reflected light, so that the reflected light is reproduced, but the diffracted light by the hologram is mainly the 0th order diffracted light. , +
First-order diffracted light and -1st-order diffracted light are generated. Therefore, in digital holography, an image by the 0th-order diffracted light, an image by the + 1st-order diffracted light, that is, a real image and an image by the -1st-order diffracted light,
That is, the three images of the virtual image are reproduced.
What you want to acquire as an object image is either a real image or a virtual image. When the reference light and the reflected light are coaxial, the three images are reproduced by overlapping. Therefore, in off-axis digital holography, a tilt is given to both axes and a carrier frequency is generated in the interference fringes. Record at. As a result, the 0th-order light, the real image, and the virtual image are reproduced separately, so that the real image or the virtual image can be extracted.

The reproduction operation in off-axis digital holography is generally Fresnel conversion with the reproduction distance (distance from the digital light receiving element in the optical axis direction of the optical system to the image reproduction position) as a parameter. For the Fresnel transform, refer to “Naoki Aoki“ Numerical Two-Dimensional Fresnel Transform Method ”, IEICE Transactions, '74 / 8 Vol.57-B No.8 (197).
4) ”, when the distance from the aperture plane (corresponding to a hologram here) to the image reproduction position is short,
That is,

[Equation 2] When the condition of is satisfied, the FFT operation can be executed twice.
On the contrary, when the distance is long, that is,

[Equation 3] Under the condition of, the FFT operation can be performed once. In the equations (1) and (2), d is the reproduction distance, L is the size of the image pickup surface in one direction of the light-receiving digital element (for example, the X direction of the XY coordinate system), λ is the wavelength of the light source,
M represents the number of pixels (the number of data) in one direction of the digital light receiving element.

According to one FFT calculation, the reproduction image becomes smaller as the reproduction distance d becomes larger, and the reproduction position of the image shifts in the plane perpendicular to the optical axis of the optical system. FIG. 1 shows an outline of the situation. In FIG. 1, reference numeral 1 is a real image in the reproduced image, reference numeral 2 is an image by 0th order light, reference numeral 3 is a virtual image, and in off-axis digital holography, 0th order light Since it is necessary to make d large in order to separate the image from the real image and the virtual image, the position and size of the reproduced image change with the reproduction distance. That is,
In FIG. 1, the reproduction distance d increases and the reproduced image decreases in the order of (a) to (c).

In this case, for example, steps 4 to 6 as shown in FIG.
Record a three-dimensional object with a step structure consisting of
When trying to reproduce by focusing on the surface of, the image when focusing on step 4, the image when focusing on step 5, and the image when focusing on step 6, Position of,
The size will be different. In digital holography, focusing by numerical calculation is possible, and its function can be applied to various applications such as generation of an omnifocal image that is in focus in the entire field of view. If the size changes, the application of the omnifocal image becomes difficult, such as the difficulty in generating the omnifocal image.

The object of the present invention is to correct the above-mentioned difference in the position and size of the real image and virtual image due to the difference in the position of the interference optical system in the optical axis direction, thereby performing image reproduction by holography and the surface shape of the object to be measured. Is to improve functionality and versatility.

[0009]

According to a first aspect of the present invention, there is provided interference fringe data which is image data of an interference fringe obtained by imaging an interference fringe between a reflected light on an object to be measured and a predetermined reference light. Based on the optical data detection means to obtain the complex amplitude data consisting of the phase data indicating the phase of the reflected light of the measured object at a plurality of positions in the optical axis direction of the reflected light and the amplitude data indicating the amplitude by Fresnel analysis calculation, Image reproduction means for determining a focus state in the amplitude data and converting the amplitude data into an image of a real image or a virtual image of the object to be measured, wherein the image reproduction means is a zero-order diffracted light in the complex amplitude data. Is adjusted so that the center of the image becomes a predetermined position on the reproduced image, and the center of the image of the 0th-order diffracted light in the adjusted complex amplitude data and the real image or the imaginary image in the complex amplitude data are adjusted. The distance from the center of the reproduced image on the reproduced image is obtained, and the conversion according to the position difference in the optical axis direction is performed by enlarging or reducing the real image or the virtual image with the center of the real image or the virtual image in the complex amplitude data as a reference. It is a holographic device that corrects the difference in the position and size of a real image or a virtual image afterwards.

Therefore, it is possible to improve the functionality and versatility of image reproduction by holography by correcting the difference in the position and size of the real image or the virtual image due to the difference in the position of the reflected light of the object to be measured in the optical axis direction. it can.

According to a second aspect of the present invention, the reflected light is based on the interference fringe data which is image data of the interference fringe obtained by imaging the interference fringe between the reflected light on the object to be measured and a predetermined reference light. Optical data detecting means for obtaining complex amplitude data consisting of phase data indicating the phase of the reflected light of the object to be measured and amplitude data indicating the amplitude at a plurality of positions in the optical axis direction by Fresnel analysis calculation, and focusing on the amplitude data. Shape data creating means for determining a state and converting the amplitude data into shape data of the surface of the object to be measured, wherein the shape data creating means is such that the center of the image of the 0th-order diffracted light in the complex amplitude data is The image is adjusted to a predetermined position on the reproduced image, and the center of the image of the 0th-order diffracted light in the adjusted complex amplitude data and the real or virtual image in the complex amplitude data are adjusted. Obtaining the distance on the reproduced image from the center, by enlarging or reducing the real image or virtual image with the center of the real image or virtual image in the complex amplitude data as a reference, after the conversion due to the difference in the position in the optical axis direction. Is a holographic device that corrects the difference in the position and size of the real image or the virtual image.

Therefore, the function of measuring the surface shape of the measured object using holography is corrected by correcting the difference in the position and size of the real image or the virtual image due to the difference in the position of the reflected light of the measured object in the optical axis direction. The versatility can be improved.

According to a third aspect of the present invention, the reflected light is based on the interference fringe data which is image data of the interference fringe obtained by imaging the interference fringe between the reflected light on the object to be measured and a predetermined reference light. Optical data detecting means for obtaining complex amplitude data consisting of phase data indicating the phase of reflected light of the object to be measured at a plurality of positions in the optical axis direction and amplitude data indicating the amplitude by Fresnel analysis calculation, and using the amplitude data First surface shape data creating means for determining a focused state and obtaining first surface shape data which is surface shape data of the object to be measured, and surface shape data of the object to be measured using the phase data. The second to obtain the second surface shape data
Surface shape data creating means, and the synthesizing means for synthesizing the first surface shape data and the second surface shape data to obtain the third surface shape data which is the surface shape data of the object to be measured. And the adjusting means adjusts the center of the image of the 0th-order diffracted light in the complex amplitude data to a predetermined position on the reproduced image, and adjusts the 0th-order diffracted light in the adjusted complex amplitude data. Obtaining the distance on the reproduced image of the center of the image and the center of the real image or the virtual image in the complex amplitude data, by enlarging or reducing the real image or the virtual image with the center of the real image or the virtual image in the complex amplitude data as a reference, It is a holography device that corrects a difference in position and size of the combined real image or virtual image due to a difference in position in the optical axis direction.

Therefore, by correcting the difference in the position and size of the real image or virtual image due to the difference in the position of the reflected light of the measured object in the optical axis direction, the functionality of measuring the surface shape of the measured object using holography is corrected. The versatility can be improved.

The invention described in claim 4 is the same as claim 1
In the holographic device according to any one of 1 to 3,
A light source that emits light for irradiating the object to be measured, an interference optical system that generates interference fringes between the reflected light of the light and the predetermined reference light on the object to be measured, and the interference fringes by imaging the interference fringes. And an image sensor that outputs interference fringe data that is image data of the image.

Therefore, the interference fringe data of the object to be measured can be acquired.

According to a fifth aspect of the present invention, in the holographic device according to any one of the first to fourth aspects, the image reproducing means, the shape data creating means or the synthesizing means is used for image reproduction. When the position shift amount of the 0th-order light center at the reproduction distance z is represented by the following expression P (z),

[Equation 4] (Where L is the size of the image plane of the interference fringes, λ is the wavelength of the light source when the interference fringes are imaged, M is the number of pixels (the number of data) in one direction of the image pickup device which images the interference fringes) P ( The center of the image of the 0th-order diffracted light in the complex amplitude data is set to the center position on the reproduced image by shifting the position by 1/2 of z).

Therefore, the center of the image of the 0th-order diffracted light in the complex amplitude data is adjusted to a predetermined position on the reproduced image, and a real image or a real image due to the difference in the position of the reflected light of the object to be measured in the optical axis direction. Differences in the position and size of the virtual image can be corrected.

According to a sixth aspect of the present invention, in the holographic device according to any one of the first to fifth aspects, the image reproducing unit, the shape data creating unit or the synthesizing unit is configured to reproduce the real image or the virtual image. Since the center is displaced by the number of pixels corresponding to the carrier frequency of the interference fringes with respect to the center of the image of the 0th-order light, the center of the image of the 0th-order light and the center of the real image or the virtual image are reproduced. Find the distance at.

Therefore, the distance between the center of the image of the 0th-order light and the center of the real image or the virtual image on the reproduced image is obtained, and the real image or the virtual image due to the difference in the position of the reflected light of the measured object in the optical axis direction is obtained. Position and size differences can be corrected.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION [First Embodiment of the Invention] An embodiment of the present invention will be described.

FIG. 4 is a conceptual diagram showing the overall device configuration of the hologram device according to the present embodiment. As shown in FIG. 4, this hologram device includes a He-Ne laser 11 that is a light source, an ND filter 12 for adjusting the intensity of the light emitted to an object, and a light emitted from the He-Ne laser 11. And a beam expander 13 that expands and also acts as a spatial filter.

The light expanded by the beam expander 13 and reflected by the half mirror 14 is applied to the object 15 to be measured. The light reflected by the DUT 15 passes through the half mirror 14 and reaches the CCD 16. On the other hand, the light expanded by the beam expander 13 and transmitted through the half mirror 14 passes through the ND filter 17 and is reflected by the mirror 18. Then, after passing through the ND filter 17 in the opposite direction, it is reflected by the half mirror 14 and reaches the CCD 16 which is the image pickup element. The half mirror 14, the mirror 18 and the like constitute an interference optical system.

The light reflected by the object to be measured 15 becomes reflected light, and the light reflected by the mirror 18 becomes reference light, which interfere with each other, and the interference fringes are picked up by the CCD 16, and the image is picked up via the frame grabber 19. It is transferred to the computer 20 and recorded in the memory of the computer 20.

The optical paths of the reference light and the reflected light after being split by the half mirror 14 are set to be equal to or less than the He-Ne coherence length of the light source. Also,
The intensity of irradiation light to the object to be measured 15 is adjusted by the ND filter 12 so that the reflected light from the object to be measured 15 has an intensity suitable for imaging by the CCD 16. Further, the reflected light from the object to be measured 15 is adjusted. The reference light intensity is adjusted by the ND filter 17 so that the contrast of the interference fringes generated by the interference with the reference light becomes high.

In this hologram device, the interference fringes are treated as holograms, the hologram interference fringes picked up by the CCD 16 are virtually irradiated with reference light, and the diffracted light waves reflect the reflected light of the object 15 (object 15 to be measured). Image) is reproduced.

When a single interference fringe data is imaged by the CCD 16 and the reflected light of the object to be measured 15 is reproduced, the 0th-order diffracted light passing through the hologram, the real image, and the virtual image are reproduced, so these 3 In order that the two can be reproduced separately, an appropriate inclination is given between the optical axis of the reflected light of the DUT 15 and the optical axis of the reference light so that the carrier frequency is placed on the interference fringes. In order to give an inclination to both the optical axes, the inclination of the mirror 18, the DUT 15, or the half mirror 14 may be adjusted, for example.

Next, the reflected light from the DUT 15 (DUT 1
A method of reproducing and calculating the complex amplitude of the image (5) will be described.

The intensity on the image pickup surface of the CCD 16 of the interference fringes generated by the interference between the reflected light of the DUT 15 and the reference light is given by the equation (3).

[Equation 5] Here, I is the intensity of the interference fringes, and x and y are the CCD 16
Represents the position in coordinates of the image pickup surface of. R represents the complex amplitude of the reference light, and A and φ represent the amplitude and phase of the reflected light of the DUT 15, respectively. In this specification, the amplitude and the phase are collectively referred to as a complex amplitude.

The interference fringes are picked up by the CCD 16 and stored in the computer 20 as hologram image data. In holography using a dry plate, when the dry plate (hologram) on which interference fringes are recorded is irradiated with reference light again, the reference light is diffracted by the interference fringes recorded on the hologram, and it behaves as reflected light at the time of recording. Therefore, the reflected light (object image) is reproduced. Here, it is assumed that the hologram is virtually irradiated with the reference light without actually irradiating the reference light, and the reflected light (object image) is reproduced from the hologram image recorded by the CCD 16 based on Fresnel approximation. Assuming that the hologram is irradiated with parallel light as reference light, diffracted light by the hologram, that is, reflected light, is expressed by equation (4).

[Equation 6] Where U is the complex amplitude of the reflected light wave at the image plane position separated by the reproduction distance d, and x ′ and y ′ are the coordinates at the image plane position,
C is a complex constant, and λ is a light source wavelength. Therefore, the complex amplitude of the reflected light at the reproduction distance d is reproduced by inputting the reproduction distance d and calculating the equation (4) using the recorded interference fringe data.

In the reproduced image, the light (0
Three images of a real image and a virtual image are included, and in order to obtain the shape of the DUT 15, attention is paid to the real image or the virtual image. When the optical axes of the reflected light and the reference light are nearly parallel during recording of the hologram image, these three images are reproduced in an overlapping manner, and as described above, the relative axes of the reflected light and the reference light are relative to each other. Give a nice inclination,
A hologram (interference fringe image) is created with the carrier frequency placed on the interference fringes, and by doing so, these three images can be reproduced at distant positions at the image plane position. Let the real part of the complex amplitude represented by equation (4) be Real {U
(X ', Y')}, and the imaginary part is Imaginary {U (X ',
Y ′)}, the amplitude A and the phase φ of the reflected light of the DUT 15 are given by the following equations (5) and (6), respectively. A calculated by the equation (5) and φ calculated by the equation (6) correspond to the amplitude data and the phase data, respectively.

[0032]

[Equation 7]

[0033]

[Equation 8]

As described above, according to the reproduction distance (d in the equation (4)), the real image reproduced when the image is reproduced,
The position and size of the virtual image change. In order to prevent such a change, the following first to third stages of calculation using the reproduction distance as a parameter may be performed.

(1) First Stage First, adjustment is made so that the center of the 0th-order light comes to the center of the screen regardless of the reproduction distance. Considering the aperture size on the Fresnel conversion surface, the size change rate S of the reproduced image depending on the reproduction distance
(D) is

[Equation 9] (In Expressions (7) and (8), L is the size of the imaging surface,
λ: wavelength of light source, M: number of data, z: reproduction distance),
The size of the reproduced image is obtained by multiplying S (d) by the original image size.

Therefore, the positional deviation amount P of the 0th-order light center
(Z) is expressed by equation (8), and when the position of the reproduced image is shifted by 1/2 of P (d), the 0th-order light center is always at the center of the display image.

[0037]

[Equation 10]

(2) Consider the positional deviation of the real image with respect to the second stage 0th order light. That is, the distance on the reproduced image between the center of the 0th-order light image and the center of the real image or the virtual image is obtained. The reproduction calculation assumes a physical phenomenon that parallel light is incident on the hologram and diffracts it. Therefore, the 0th order light in the reproduced image is the transmitted light of the hologram (diffraction grating), the real image is the + 1st order diffracted light, and the virtual image is -1. It can be considered as the second-order diffracted light. Therefore, from the diffraction formula, the positional deviation D of the + 1st order diffracted light with respect to the transmitted light is

[Equation 11] Becomes

In the equation (9), t is the grating interval of the diffraction grating, which corresponds to the interval of the interference fringes in the hologram. Therefore, using the carrier frequency f of the interference fringe,

[Equation 12] Can be expressed as

Since the size change rate represented by the equation (7) is also applied to the size of the real image as in the case of the 0th order light, the positional deviation J (d) of the real image from the 0th order light is as follows.

[Equation 13] Becomes

From equation (11), it can be seen that the positional deviation J (d) of the real image with respect to the 0th order light is constant regardless of the reproduction distance and equal to the carrier frequency. The carrier frequency is obtained by, for example, extracting intensity distribution data of the X-direction cross section and the Y-direction cross section of the interference fringe image, performing Fourier transform on them, and obtaining a frequency component that becomes a peak when the low-frequency component is removed. be able to. Therefore, the center of the real image or the virtual image is at a position displaced by the number of pixels corresponding to the carrier frequency of the interference fringes with respect to the center of the image formed by the 0th-order light, regardless of the reproduction distance. 0 like that
Find the deviation of the real or virtual image from the image due to the next light. The carrier frequency is the cross section of the image in all X directions, and all Y directions.
It is also possible to obtain each of the directional cross sections and use the average value thereof.

(3) Third step Correct the change in size of the real image or virtual image due to the change in reproduction distance. As the method, the center of the real image or virtual image obtained as described above is used as the center for enlargement or reduction, and the size of the real image or virtual image is enlarged or reduced according to the reproduction distance. The reference image size for enlargement / reduction is, for example, when the size is the smallest of the real image or the virtual image obtained by a plurality of reproduction distances, and the enlargement / reduction ratio is d / d ′ ( d: playback distance,
d ': the reproduction distance when the size of the real image or the virtual image is the smallest). As a result, the position and size of the real image or virtual image in the reproduced image are constant regardless of the reproduction distance.

In digital holography, (4)
Focusing by numerical calculation can be performed by changing the reproduction distance d in the formula. By using this function, for example, an omnifocal image in which the entire field of view is in focus can be generated.

The concept of this omnifocal image generating means is shown in FIG.
Will be explained. FIG. 5 shows an object and a hologram surface (CC
5 shows the positional relationship between the image pickup position of D16) and the reproduced image. In FIG. 5, reference numeral 21 is an object, reference numeral 22 is a hologram surface, and reference numeral 23 is a reproduced image of the object 21. If the reproduction distance d is -x1 when the hologram surface is the origin,
When the real image of the surface at the position of x1 is reproduced in a focused state, and similarly, when the reproduction distance d is -x2, -x3, the real images of the surfaces at the positions of x2 and x3 are in a focused state, respectively. It indicates that it will be played.

In this case, for example, when "d = -x1" is set, the surfaces at x2 and x3 are out of focus. Therefore, while changing the reproduction distance d, the complex amplitude of the reflected light wave at each reproduction distance is obtained by the formula (4), the real image or virtual image of the amplitude data at the complex amplitude is obtained, and the in-focus area is two-dimensionally determined. If an image is generated by connecting to, it is possible to obtain an omnifocal image in focus in all observation fields of view.

In order to determine whether or not the focal point is in focus, a plurality of complex amplitudes are calculated by using the equation (4) while changing the reproduction distance d by a small amount, and the amplitude data at each reproduction distance is calculated as (5 ). Then, for each amplitude data, the contrast or intensity in an arbitrary small area in the real image or virtual image portion of the image pickup position of the CCD 16 is obtained.

The contrast represents the in-focus state of the texture on the surface to be measured of the object 15 to be measured, and there are various calculation methods. For example, the contrast can be obtained by calculating the variance of amplitude data in a small area. . The intensity can be obtained by calculating the total value or average value of the amplitude data in the small area. If the texture is clearly observed on the surface to be measured, contrast may be used.If no clear texture is observed on the surface of the mirror or glass, use intensity or image on the surface to be measured. It is also possible to project a different intensity pattern and utilize it as a texture. The calculation of those contrasts and intensities is for knowing the in-focus state of the area, and another calculation method for knowing the in-focus state may be used. Further, although the above description is made assuming that the amplitude data is used, intensity data obtained by squaring the amplitude data may be used. When the reproduction distance is changed, the contrast becomes the highest in the small area or the intensity becomes the strongest, which is the focusing distance in the small area.

FIG. 6 shows the change in contrast when the reproduction distance d is changed in an arbitrary small area of the image picked up by the CCD 16. The position D in FIG. 6 is the focusing distance. Therefore, if the focusing distance is obtained in all small areas in the real image or the virtual image and the amplitude data at the focusing distance is used as the image data of the real image or the virtual image, an omnifocal image having a focus in the entire visual field can be generated. You can

FIG. 7 is a flow chart showing a concrete flow when the computer 20 performs the arithmetic processing described above. First, as described above, the interference fringes of the reflected light reflected by the DUT 15 and the reference light are generated (step S
1), the hologram image of the interference fringe is picked up by the CCD 16 and the interference fringe data is recorded in the memory of the computer 20 (step S2).

Then, the value k of a predetermined counter is initialized (= 0) (step S3), and the reproduction distance d is changed at a pitch of Δd from the initial value d0 (step S3).
4, S6), and the data of the complex amplitude at each reproduction distance (dk) is obtained as described above (step S5).
The required number K of data of this complex amplitude is obtained (step S7).

Next, for example, the contrast in a small area, which is a real image or a virtual image portion of the image pickup position of the CCD 16, is obtained as described above (step S8), and the focusing distance in the outer phase area is described above. 1 to 3 (step S9), and the amplitude data at the focus distance is replaced with the image data of the real image (or virtual image) as described above (step S10).
Is performed for all the small areas (step S11), and the omnifocal image is output (step S12).

Then, when the amplitude data at the focusing distance is replaced with the image data of the real image (or the virtual image) (step S10), at each position of the image, as shown in FIG.
The process of is executed. That is, the center of the 0th-order light is adjusted so as to come to the center of the screen regardless of the reproduction distance d (the above-mentioned first
Step processing) (step S21), the distance D on the reproduced image between the center of the 0th-order light image and the center of the real image or the virtual image is obtained (the above-described second step processing) (step S22), and the reproduction distance D Of the change in the size of the real image or the virtual image due to the change in the above (the above-mentioned third stage processing) (step S2).
3).

Therefore, according to this hologram device, even if the reproduction distance is changed, the position and size of the image are not changed, so that it is possible to compare the contrasts (or intensities) of minute areas, and the omnifocal image is obtained. Can be generated.

[Second Embodiment of the Invention] A hologram apparatus according to another embodiment will be described.

The hardware configuration of this hologram apparatus is the same as that of the first embodiment, and the same reference numerals are used and detailed description thereof is omitted.

The difference from the first embodiment is that the process of FIG. 9 is performed instead of the process of FIG. Also in the process of FIG. 9, steps S1 to S9 and 11 are common to the case of the first embodiment, and detailed description thereof will be omitted. In the second embodiment, step S13 is performed instead of step S10. That is, in the first embodiment, the focusing distance in the small area of the real image or the virtual image is obtained in the process of generating the omnifocal image. Since these indicate how far each small region of the real image or the virtual image is from the hologram (the image pickup surface of the CCD 16), the focus distance is used as the shape data of the DUT 15 (step S13), The shape of the DUT 15 is obtained by connecting the shape data in all the small areas (step S14). Then, in step S13, as in the case of the first embodiment, the processes of steps S21 to S23 are executed.

In this case as well, it is possible to compare the contrast and intensity of small areas by correcting the change in the position and size of the image due to the difference in the reproduction distance, and it is possible to perform accurate shape measurement.

[Third Embodiment of the Invention] A hologram apparatus according to another embodiment will be described.

FIG. 10 is a conceptual diagram showing the overall configuration of the hologram device according to this embodiment. As shown in FIG. 10, this hologram device includes a He—Ne laser 24 that is a light source, an ND filter 25 for adjusting the intensity of irradiation light to the DUT 15, and a light from the He—Ne laser 24. A beam expander 26 that expands and also functions as a spatial filter is provided.

The light expanded by the beam expander 26 is reflected by the mirror 27 and enters the beam splitter 28. The light reflected by the beam splitter 28 passes through a lens 29 for converting the light into a spherical wave, is reflected by a mirror 30, and is an ND filter 3 for adjusting the light intensity.
1. CCD which is an image sensor passing through the half mirror 32
Reach 33. This light serves as reference light for interfering with the reflected light of the DUT 15.

On the other hand, the light transmitted through the beam splitter 28 is reflected by the mirror 34, converted into a spherical wave by the lens 35, transmitted through the half mirror 32, converted into substantially parallel light by the objective lens 36, and is converted into a substantially parallel light. The measurement object 15 is irradiated with light. The light reflected by the DUT 15 passes through the objective lens 36, is reflected by the half mirror 32, reaches the CCD 33 as reflected light, and interferes with the reference light to generate interference fringes. The mirrors 27, 30, 34, 32, the beam splitter 28, the lenses 29, 35, 36, etc. constitute an interference optical system.

The interference fringes are picked up by the CCD 33 and transferred to the computer 39 via the frame grabber 38.
It is recorded in the memory of the computer 39. The optical paths of the reference light and the reflected light after being split by the beam splitter 28 are set to be equal to or less than the He-Ne coherence length of the light source. In addition, N is adjusted so that the reflected light of the DUT 15 has an intensity suitable for imaging with the CCD 33.
The intensity of the irradiation light to the DUT 25 is adjusted by the D filter 25, and the ND filter 31 is used to increase the contrast of the interference fringes generated by the interference between the reflected light of the DUT 15 and the reference light. The reference light intensity is adjusted. The objective lens 36 acts so as to convert the reflected light of the DUT 15 into a spherical wave, and as a result, the complex amplitude data of the reflected light of the DUT 15 (image of the DUT 15) will be described later.
When reproduced, the image is enlarged and observed. Lens 3
The positional relationship between 5 and the objective lens 36 is adjusted so that the object to be measured 15 is irradiated with substantially parallel light. Lens 29
Acts so as to convert the reference light into a spherical wave, so that the curvature of the reflected light of the DUT 15 converted into the spherical wave by the objective lens 36 and the curvature of the reference light substantially match on the CCD surface. The position has been adjusted. If the image of the DUT 15 is not magnified, the objective lens 36 becomes unnecessary,
Accordingly, the lens 29 and the lens 35 are also unnecessary.

As described above, in the off-axis digital holography, since the three images of the 0th-order diffracted light, the real image, and the virtual image are reproduced, the reflection of the object 15 to be measured so that these three can be reproduced separately. An appropriate inclination is given between the optical axis of the light and the optical axis of the reference light so that the carrier frequency lies on the interference fringes. In order to give an inclination to both the optical axes, the inclination of the mirror 30, the DUT 15, or the half mirror 32 may be adjusted. The complex amplitude of the reflected light at an arbitrary reproduction distance can be obtained by calculating the equation (4) using the interference fringe data captured by the CCD. Using the complex amplitude, the amplitude data and the phase data of the reflected light can be obtained by the equations (5) and (6).

When the image of the object to be measured 15 is not enlarged, the distance between the image pickup surface of the CCD 33 and the surface of the object to be measured 15 may be input as the reproduction distance d. When the image of the object to be measured 15 is magnified as in the apparatus shown in FIG. 10, the distance between the magnified image plane of the object to be measured 15 by the objective lens and the imaging surface of the CCD 33 is input as the reproduction distance d.

FIG. 11 shows the object 15 to be measured, the objective lens 36, and the hologram surface (imaging surface of the CCD 33) shown in FIG.
3A and 3B show the positional relationship between the magnified images of the object 15 to be measured by the objective lens 36.

In FIG. 11, reference numeral 40 is the DUT 1.
5, reference numeral 41 is an objective lens, reference numeral 42 is a hologram, 4
3 is an enlarged image plane of the object 15 to be measured by the objective lens 41. The reproduction distance is represented by d ′ in FIG. 11, which is input into the equation (4) to reproduce and calculate the image of the DUT 15. Since s and s ′ have the relationship of the lens imaging formula (12), s ′ can be obtained by knowing the focal length f of the objective lens and the object distance s in advance.

[0067]

[Equation 14]

The surface shape of the DUT 15 is obtained with an accuracy of not more than the wavelength of the light source by converting the phase φ obtained by the equation (6) into a unit of length and unwrapping it if there is a phase jump. However, if there is a discontinuous area on the surface of the DUT 15, the phase continuity is interrupted in that area. Therefore, the difference in relative depth (height) at each position of the surface shape of the DUT 15 becomes unclear.

In the present embodiment, the amplitude data of the complex amplitude data acquired by observing the object to be measured 15 is used to obtain the difference in depth between the surfaces sandwiching such a discontinuous area. The shape of the surface to be measured is measured. When the measurement resolution in that case is smaller than λ / 2, the shape (depth) data obtained by using the amplitude data and the shape data obtained by the phase data are combined to generate the object to be measured 15 based on the phase. It is possible to eliminate the uncertainty associated with the light source wavelength in the shape data of each surface position of.

That is, for the shape measurement using the amplitude data, the means described in the first and second embodiments may be used, and the shape data Sij (i: in the X direction of the image) for all the pixels forming the real image or the virtual image. Coordinates, j: coordinates in the Y direction of the image) are obtained.

When obtaining the contrast or the intensity in a small area, the complex of the reflected light of the DUT 15 at a plurality of positions in the approximate optical axis direction of the reflected light of the DUT 15 is gradually changed while changing the reproduction distance d little by little. The amplitude data is obtained by calculation. In that case, the interval (pitch) of the change in the reproduction distance is 1 of the wavelength of the light output from the laser 24, which is the light source.
It is better to be less than / 2. However, the focus distance may be obtained by approximating a plot of a plurality of focus measures to a function such as a Gaussian function and obtaining the vertices of the function. In that case, the interval of the above-mentioned reproduction distance change is strictly the light source. Wavelength 1
It does not have to be less than / 2.

Here, the measurement sensitivity γ in the vertical direction of the measurement using the amplitude data is calculated by using the constant k and the magnification β of the optical system.

[Equation 15] The measurement sensitivity increases in inverse proportion to the square of the magnification of the optical system.

On the other hand, the difference in the depth of the surface shape in the region sandwiching the discontinuous region is measured by a method using amplitude data,
When trying to combine with the shape measured by the phase data,
Measurement resolution of less than half the source wavelength is required for methods that use amplitude data. Since the wavelength of light is several hundreds of nm in the case of visible light, the measurement resolution of measurement using amplitude data must be on the order of nm.
Considering that, it is considered difficult to satisfy the requirement of the measurement resolution using the amplitude data without enlarging the image of the DUT 15, and therefore, in the configuration of FIG.
The device configuration is such that an image of the object 15 to be measured is magnified and measured using a lens.

However, when the wavelength of the light source is increased to the order of μm or mm, the measurement resolution requirement of the measurement using the amplitude data can be satisfied without enlarging the image of the DUT 15, and the measurement can be performed. It will be possible.

Next, a method of obtaining the surface shape using the phase data calculated by the equation (6) will be described.

For that purpose, the phase calculated by the equation (6) may be converted into a unit of length to obtain the surface shape of the DUT 15. In this case as well, in all the pixels forming a real image or a virtual image, The shape data Tij of the surface of the object 15 to be measured (i: coordinates in the X direction of the image, j: coordinates in the Y direction of the image) are obtained.

The reproduction distance when the phase data is obtained is as follows. The reproduction distance is the focusing distance obtained by the measurement using the amplitude data in each small area, and Fresnel conversion is performed for each small area. Although the phase data may be obtained, the calculation time is long because the Fresnel transform is executed many times.

Therefore, for example, a reference distance (for example, the initial value d0 of the reproduction distance described above) is set, and Fresnel conversion is executed using this as the reproduction distance, and the phase data obtained by this is used for each small region. Alternatively, the Fresnel transform is performed with the average value of the focusing distances used in all the small areas in the shape measurement using the amplitude data as the reproduction distance,
The phase data obtained thereby may be used in each small area. In these cases, the Fresnel transform for obtaining the phase data only needs to be executed once.

As in the apparatus shown in FIG. 10, when the image of the object 15 to be measured is magnified using a lens, if the curvature of the reflected light of the object 15 to be measured and the curvature of the reference light do not match, The measured value of the phase includes concentric defocus aberration due to the difference in curvature as shown in FIG. Therefore, in order to accurately obtain the shape, it must be removed. To this end, in the device configuration of FIG. 10, when the positions of the lenses 26, 29, 35 and the like are adjusted so that the curvature of the reflected light of the DUT 15 and the curvature of the reference light are substantially the same, the difference between the two curvatures is obtained. Therefore, the defocus aberration is not included in the phase data.

Next, the shape Sij obtained from the amplitude data
And means for synthesizing the shape Tij obtained from the phase data will be described. A shape that is not affected by the discontinuous area,
That is, the composite shape Zij is expressed as in equation (14).

[0081]

[Equation 16]

In the equation (14), Zij is a composite shape,
mij is the order, λ is the light source wavelength, and Tij is the shape obtained from the phase data. The subscript i in equation (14) is the X of the image.
Represents the coordinate in the direction, and j represents the coordinate in the Y direction of the image. In the measurement using only the phase data, the order mij becomes unclear between the surfaces sandwiching the discontinuity region. However, by specifying the order mij in equation (14), the above unclearness is resolved. can do. Therefore, the shape Sij obtained from the amplitude data is used, and the integer of the quotient when Sij is divided by the wavelength λ is the order mij. Therefore, if the mij is substituted into the equation (14), the combined shape Zij
Is obtained.

FIG. 3 shows a micromirror ray 9 as an example of the object to be measured 15. In FIG. 3, reference numerals 7a to 7d are mirrors as the surface to be measured, and a gray area around the mirrors is an unnecessary invalid area. Therefore, the respective mirror surfaces are discontinuous with each other, and the relative difference in depth (height) between the surfaces of the mirrors 7a to 7d is unclear. A micromirror ray is an element that mainly modulates the angle and position of reflected light by changing the angle and position of each constituent mirror independently, and is used in image modulation devices for display and optical equalizers. To be Each constituent mirror moves independently and often requires high-speed operation.

In the measurement when the object to be measured 15 is the micromirror ray 9, since the phase data in each of the independent mirrors 7a to 7d is continuous, the composite shape is obtained in a partial area of each mirror surface. The combined shape Zij can be obtained over the entire surface to be measured by performing the phase unwrapping by comparing the adjacent pixels with respect to the combined shape.

Specific processing performed by the computer 39 will be described with reference to the flowchart of FIG.
As shown in FIG. 13, the processes of steps S1 to S11 are the same as those in the first embodiment, and thus detailed description thereof will be omitted. Through the processing of steps S1 to S11, the shape Sij is obtained (step S31), and the shape Sij is calculated.
Is divided by the wavelength to obtain the order mij (step S3
2). Next, as described above, the shape Tij is obtained from the phase data at the reproduction distance d0 (step S33).
Then, as described above, the composite shape Zij is calculated (step S34), and the composite shape Zij is output (step S35).

Then, when the composite shape Zij is calculated (step S34), as in the first and second embodiments, FIG.
The process of is executed. That is, the center of the 0th-order light is adjusted so as to come to the center of the screen regardless of the reproduction distance d (the above-mentioned first
Step processing) (step S21), the distance D on the reproduced image between the center of the 0th-order light image and the center of the real image or the virtual image is obtained (the above-described second step processing) (step S22), and the reproduction distance D The change in the size of the real image (or virtual image) due to the change in (the above-mentioned third stage processing) (step S2).
3).

According to the hologram device described above, C
For an object that moves at a speed sufficiently slower than the imaging time of the CD 33, it is possible to measure the dynamic shape of the moving moment. However, when the movement of the object becomes faster and becomes faster than the image pickup time of the CCD 33, the object to be measured 15 is picked up during the image pickup.
Since the intensity and phase of the reflected light changes, the complex amplitude of the reflected light cannot be accurately obtained. In such a case, if the pulsed light is irradiated to the measured object 15 in a sufficiently short time with respect to the moving speed of the measured object 15 and the reflected light is received, the measured object is irradiated during the light irradiation. Since the object 15 can be regarded as being apparently stationary, the reflected light of the object 15 to be measured is stable, its complex amplitude can be accurately determined, and accurate dynamic shape measurement of the object becomes possible.

In the first to third embodiments, a solid-state laser that outputs pulsed light such as a ruby laser or a YAG laser may be used as a light source for irradiating the DUT 15 with pulsed light. A semiconductor laser that outputs light may be used, or a semiconductor laser that outputs CW light may be pulse-modulated to generate pulsed light. He-Ne
CW light from a laser or an argon laser may be pulsed and used using a rotary chopper.

Further, instead of irradiating the object to be measured 15 with pulsed light, if the CCDs 16 and 33 are replaced with a high-speed camera capable of high-speed imaging, the same effect as pulsed light source can be obtained.

[0090]

INDUSTRIAL APPLICABILITY The present invention corrects the difference in the position and size of the real image or the virtual image due to the difference in the position of the reflected light in the optical axis direction of the object to be measured, and reproduces the image by holography or the object to be measured using holography. The functionality and versatility of the measurement of the surface shape can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram illustrating a problem of the present invention.

FIG. 2 is an explanatory diagram illustrating a problem of the present invention.

FIG. 3 is an explanatory diagram of a micromirror ray which is an example of an object to be measured.

FIG. 4 is a conceptual diagram showing a schematic configuration of a hologram device that is Embodiment 1 of the present invention.

FIG. 5 is a conceptual diagram of a means for generating an omnifocal image.

FIG. 6 is a graph showing a change in contrast when a reproduction distance d is changed in an arbitrary small area of an image picked up by a CCD.

FIG. 7 is a flowchart of processing performed by the hologram device.

FIG. 8 is a flowchart of processing performed by the hologram device.

FIG. 9 is a flowchart of processing performed by the hologram device according to the second embodiment of the present invention.

FIG. 10 is a conceptual diagram showing a schematic configuration of a hologram device that is Embodiment 3 of the present invention.

FIG. 11 is an explanatory diagram illustrating the positional relationship between the measured object, the objective lens, the hologram surface, and the magnified image of the measured object by the objective lens.

FIG. 12 is an explanatory diagram illustrating concentric defocus aberrations.

FIG. 13 is a flowchart of processing performed by the hologram device.

[Explanation of symbols]

11 light source 14 Interference optical system 16 Image sensor 18 Interference optical system 27 Interference optical system 30 Interference optical system 34 Interference optical system 32 Interferometric optical system 28 Interference optical system 29 Interference optical system 33 Image sensor 35 Interference optical system 36 Interference optical system

Claims (6)

[Claims] 1. A plurality of positions in the optical axis direction of the reflected light based on interference fringe data, which is image data of the interference fringe obtained by imaging the interference fringe between the reflected light on the object to be measured and a predetermined reference light. In optical data detection means for obtaining complex amplitude data consisting of phase data indicating the phase of the reflected light of the object to be measured and amplitude data indicating the amplitude by Fresnel analysis calculation, and determining the focus state in the amplitude data, the amplitude Image reproducing means for converting the data into an image of a real image or a virtual image of the object to be measured, wherein the image reproducing means is such that the center of the 0th-order diffracted light image in the complex amplitude data is at a predetermined position on the reproduced image. And the distance on the reproduced image between the center of the image of the 0th-order diffracted light in the complex amplitude data after the adjustment and the center of the real image or the virtual image in the complex amplitude data, The difference in the position and size of the converted real image or virtual image due to the difference in position in the optical axis direction is corrected by enlarging or reducing the real image or virtual image with reference to the center of the real image or virtual image in the complex amplitude data. A holographic device. 2. A plurality of positions in the optical axis direction of the reflected light based on interference fringe data which is image data of the interference fringe obtained by imaging the interference fringe between the reflected light on the object to be measured and a predetermined reference light. In optical data detection means for obtaining complex amplitude data consisting of phase data indicating the phase of the reflected light of the object to be measured and amplitude data indicating the amplitude by Fresnel analysis calculation, and determining the focus state in the amplitude data, the amplitude Shape data creating means for converting data into shape data of the surface of the object to be measured, wherein the shape data creating means is such that the center of the 0th-order diffracted light image in the complex amplitude data is at a predetermined position on the reproduced image. On the reproduced image of the center of the image of the 0th-order diffracted light in the complex amplitude data and the center of the real image or the virtual image in the complex amplitude data after the adjustment. The distance required,
By expanding or reducing the real image or the virtual image with the center of the real image or the virtual image in the complex amplitude data as a reference, the difference in the position and size of the converted real image or the virtual image due to the difference in the position in the optical axis direction is corrected. A holographic device. 3. A plurality of positions in the optical axis direction of the reflected light based on interference fringe data which is image data of the interference fringe obtained by imaging the interference fringe between the reflected light on the object to be measured and a predetermined reference light. In the optical data detection means for obtaining complex amplitude data consisting of phase data indicating the phase of the reflected light of the object to be measured and amplitude data indicating the amplitude by Fresnel analysis calculation, and determining the focus state using the amplitude data, First surface shape data creating means for obtaining first surface shape data which is data of the surface shape of the object to be measured, and second surface shape which is data of the surface shape of the object to be measured using the phase data. A second surface shape data creating means for obtaining data, a third surface which is data of the surface shape of the object to be measured by synthesizing the first surface shape data and the second surface shape data. A synthesizing unit for obtaining shape data, wherein the synthesizing unit adjusts the center of the image of the 0th-order diffracted light in the complex amplitude data to a predetermined position on the reproduced image, and adjusts the complex amplitude. The distance on the reproduced image between the center of the image of the 0th-order diffracted light in the data and the center of the real image or the virtual image in the complex amplitude data is obtained, and the real image or the virtual image is enlarged with the center of the real image or the virtual image in the complex amplitude data as a reference. A holography device that corrects a difference in position and size of the combined real image or virtual image due to a difference in position in the optical axis direction by reducing the size. 4. A light source that emits light for irradiating an object to be measured, an interference optical system that generates interference fringes between the light reflected by the object to be measured and a predetermined reference light, and an image of the interference fringes. The holographic device according to claim 1, further comprising: an image sensor that outputs interference fringe data that is image data of the interference fringe. 5. The image reproducing means, the shape data creating means, or the synthesizing means represents the amount of positional deviation of the 0th-order light center when the reproduction distance is z at the time of image reproduction, by the following formula P (z). When, (Where L is the size of the image plane of the interference fringes, λ is the wavelength of the light source when the interference fringes are imaged, M is the number of pixels (the number of data) in one direction of the image pickup device which images the interference fringes) P ( 5. The position of the image of the 0th-order diffracted light in the complex amplitude data is set to the center position on the reproduced image by shifting the position by 1/2 of z). Holographic device. 6. The image reproducing means, the shape data creating means or the synthesizing means is arranged such that the center of the real image or the virtual image is the number of pixels corresponding to the carrier frequency of the interference fringes with respect to the center of the image of the 0th order light. The holographic device according to any one of claims 1 to 5, wherein a distance between a center of an image of 0th-order light and a center of a real image or a virtual image on a reproduced image is obtained because the position is deviated.