A microstructure interference diffraction measurement device and structure restoration method thereof

Abstract

The present invention discloses an interference diffraction measuring device for microstructures and a method for restoring the structure thereof, comprising a coherent light source, wherein the light emitted by the coherent light source passes through a polarizing plate and a beam expansion and collimation system and is then divided into two paths of light by a first beam splitter prism, one path of light passing through an attenuation plate and then being reflected by a first reflector to form a reference light, and the other path of light reaching a microstructure generating device to form a diffracted light, the diffracted light passing through a second biconvex lens and then interfering with the reference light after beam combination by the second beam splitter prism, the image-side focal plane of the second biconvex lens being translated after passing through the second beam splitter prism, and the CCD photosensitive surface being placed on the translated image plane. The present invention uses an amplitude or phase modulator as a microstructure generating device and an interferometer as a microstructure interference diffraction measuring device, and can simply realize the controllable acquisition of complex microstructures and the recording and observation of interference diffraction phenomena, and only needs to perform an inverse Fourier transform on the ratio of the diffraction complex amplitude to the phase propagation factor to realize the rapid restoration of the microstructure to be measured.

Description

Technical Field

[0001] The present invention relates to an interference diffraction measuring device and a structural restoration method thereof, and in particular to an interference diffraction measuring device of a microstructure and a structural restoration method thereof. Background Art

[0002] Fourier transform holography is a lensless imaging technology widely used to restore complex two-dimensional or three-dimensional microstructures. Although this method can quickly restore complex microstructures by simply performing Fourier transform on the hologram, there are zero-order spots and conjugate images that cannot be eliminated. In 2014, Oren Raz et al. published a paper titled Direct phase retrieval in double blind Fourier holography in the journal Optics Express. They first reported the use of double-blind Fourier holography (DBFH) to restore complex two-dimensional structures. Subsequently, Ben Leshem et al. published an article titled Direct single-shot phase retrieval from the diffraction pattern of separated objects in the journal Nature Communications the following year. They used Fourier transform holography combined with the DBFH algorithm to achieve simultaneous restoration of the amplitude and phase of two tiny objects. Although the DBFH method can avoid the interference of zero-order spots and conjugate images, the algorithm implementation process is relatively complex and time-consuming. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a microstructure interference diffraction measurement device and a structure restoration method thereof. The device has a simple structure, strong operability, and a simple restoration method that is easy to implement.

[0004] Technical solution: The present invention includes a coherent light source, a polarizer, a beam expansion and collimation system, a first beam splitter prism, an attenuation plate, a first reflector, a microstructure generating device, a second biconvex lens, a second beam splitter prism and a CCD. The light emitted by the coherent light source passes through the polarizer and the beam expansion and collimation system, and then passes through the first beam splitter prism to be divided into two paths of light. One path passes through the attenuation plate and is reflected by the first reflector to form a reference light, and the other path reaches the microstructure generating device to form a diffracted light. After the diffracted light passes through the second biconvex lens, it interferes with the reference light after being combined with the second beam splitter prism. The second biconvex lens is translated after passing through the second beam splitter prism, and the CCD photosensitive surface is placed on the translated image plane.

[0005] The microstructure generating device adopts an amplitude or phase modulator, including a reflective amplitude or phase modulator and a transmissive amplitude or phase modulator.

[0006] When the microstructure generating device adopts a reflective amplitude or phase modulator, a third reflector and a second reflector are placed on the optical path in front of the microstructure generating device.

[0007] The second biconvex lens images the diffraction pattern on the image focal plane of the lens.

[0008] The second beam splitter prism causes the image plane of the diffraction pattern to shift, and the amount of shift Δl is related to the refractive index n and the thickness d of the second beam splitter prism, that is, Δl=d(1-1 / n).

[0009] The intensity of the reference light is reduced by adjusting the attenuation plate.

[0010] A method for restoring a structure of a microstructure interference diffraction measurement device comprises the following steps:

[0011] S1, using CCD to collect diffraction patterns of a standard microstructure A0 (x1, y1) with known size and a complex microstructure A (x1, y1) to be measured, as well as interference patterns of diffracted light and reference light;

[0012] S2. Obtain the amplitude of the diffracted light from the diffraction pattern of the standard microstructure A0 (x1, y1)

[0013] S3. Obtaining the phase of diffracted light from the interference pattern of a standard microstructure

[0014] S4, calculate the Fourier transform FT{A0(x1, y1)} of the standard microstructure;

[0015] S5. Calculate the exponential phase factor C(x, y);

[0016] S6. Obtain the amplitude of the diffracted light from the diffraction pattern of the microstructure A(x1, y1) to be measured

[0017] S7. Obtain the phase of the diffracted light from the microstructure to be measured from the interference pattern

[0018] S8. Ratio of the diffraction complex amplitude to the exponential phase factor of the microstructure to be measured / C(x, y) performs inverse Fourier transform to restore the microstructure to be measured.

[0019] The microstructure image used in the calculation process of S4 has the same resolution as the interference or diffraction pattern, and the Fourier transform result of the microstructure and the registration error of the diffraction pattern in the horizontal and vertical directions are both less than 1 pixel, so as to obtain the Fourier transform of the standard microstructure corresponding to the diffraction or interference pattern collected by the CCD.

[0020] The exponential phase factor / FT{A0(x1, y1)}, where λ is the laser wavelength and f is the focal length of the biconvex lens.

[0021] The diffracted light phase of the standard microstructure is obtained as follows: the interference pattern of the standard microstructure is inversely Fourier transformed to obtain the autocorrelation function of the spatially separated standard microstructure and the reference light and the cross-correlation function of the two. or right Fourier transform gives , whose phase is the phase difference between the two light paths When the reference light is incident vertically on the CCD photosensitive surface, its phase is approximately constant. At this time, the phase of the diffracted light from the standard microstructure is The phase of the diffracted light of the microstructure A(x1, y1) to be measured

[0022] Beneficial effects: The present invention uses an amplitude or phase modulator as a complex microstructure generating device and an interferometer as an interference diffraction measuring device for the microstructure, which can simply realize the controllable collection of complex microstructures and the recording and observation of interference diffraction phenomena; by placing a double convex lens in front of the CCD and placing the CCD photosensitive surface on its focal plane to collect the diffraction pattern of the microstructure, the high-frequency information of the microstructure to be measured can be retained, and the process of obtaining the complex amplitude of the diffracted light by applying Fourier holography can be simplified. Moreover, only the ratio of the diffraction complex amplitude to the phase propagation factor needs to be subjected to a two-dimensional inverse Fourier transform to realize the rapid recovery of the microstructure to be measured, and the interference of the zero-order image and the conjugate image can be eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the measuring device of the present invention, (a) the microstructure generating device is a transmission-type amplitude or phase modulator, (b) the microstructure generating device is a reflection-type amplitude or phase modulator;

[0024] Figure 2 is a flow chart of the recovery method of the present invention;

[0025] Figure 3 (a) a standard microstructure and (b) a microstructure to be tested loaded on the DMD of the present invention;

[0026] Figure 4Images collected in the experiment of the present invention: (a) is a Fraunhofer diffraction pattern of a standard microstructure collected in the experiment, (b) is an interference pattern of a standard microstructure collected in the experiment, (c) is a Fraunhofer diffraction pattern of a complex microstructure to be tested collected in the experiment, and (d) is an interference pattern of a complex microstructure to be tested collected in the experiment;

[0027] Figure 5 This is the complex microstructure restored by the algorithm of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings.

[0029] like Figure 1 and Figure 2 As shown, the measuring device of the present invention includes a coherent light source 1, a polarizer 2, a beam expansion and collimation system, a first beam splitting prism 5, an attenuation plate 6, a first reflector 7, a microstructure generating device 9, a second biconvex lens 10, a second beam splitting prism 11 and a CCD 12, wherein the beam expansion and collimation system includes a biconcave lens 3 and a first biconvex lens 4.

[0030] The coherent light emitted by the coherent light source 1 passes through the polarizer 2 and the beam expansion and collimation system, and then passes through the first beam splitter prism 5 to be divided into two paths of light. One path passes through the attenuation plate 6 and is reflected by the first reflector 7 to form a reference light, and the other path reaches the microstructure generating device 9 to form a diffracted light. After the diffracted light passes through the second biconvex lens 10, it interferes with the reference light after being combined with the second beam splitter prism 11, as shown in FIG. Figure 1 (a) is shown. The image-side focal plane of the second biconvex lens 10 is shifted after passing through the second beam splitting prism 11, and the photosensitive surface of CCD12 is placed on the shifted image plane to collect the diffraction patterns of the standard microstructure and the complex microstructure to be measured, as well as the interference pattern of the diffracted light and the reference light loaded on the microstructure generating device 9. The intensity of the diffracted light is relatively weak. In order to improve the visibility of the interference fringes, the intensity of the reference light needs to be reduced by adjusting the attenuation plate 6.

[0031] The microstructure generating device 9 uses an amplitude or phase modulator, which is a complex microstructure generating device, and can modulate the amplitude or phase of the microstructure by coding. When a reflective amplitude or phase modulator is used, such as Figure 1As shown in (b), it is necessary to place an additional second reflector 8 and a third reflector 13 on the optical path in front of it to ensure that the zero-order diffraction light of the microstructure is perpendicular to the second beam splitter prism 11. After the light is irradiated on the microstructure and diffracted, it reaches CCD12 after passing through the second biconvex lens 10 and the second beam splitter prism 11. This path of light is diffracted light. The second biconvex lens 10 images the infinitely far and infinitely large diffraction pattern within a limited range on the focal plane of the lens image side, thereby reducing the size of the interferometer and the photosensitive surface of CCD12. The second beam splitter prism 11 causes the image plane of the diffraction pattern to shift. The amount of shift Δl is related to the refractive index n and d of the beam splitter prism and its thickness, that is, Δl=d(1-1 / n). The photosensitive surface of CCD12 is placed on the image plane after the shift. The other path of light of the interferometer is the reference light. The light reaches CCD12 after passing through the attenuation plate 6 and the second beam splitter prism 11. The light intensity of the reference light can be reduced by adjusting the attenuation plate 6, so that the interference pattern has a higher fringe contrast.

[0032] like Figure 2 As shown, the restoration method of the complex microstructure to be tested of the present invention comprises the following steps:

[0033] S1, using CCD to collect diffraction patterns of a standard microstructure A0 (x1, y1) with known size and a complex microstructure A (x1, y1) to be measured, as well as interference patterns of diffracted light and reference light;

[0034] S2. Obtain the amplitude of the diffracted light from the diffraction pattern of the standard microstructure A0 (x1, y1)

[0035] S3. Obtaining the phase of diffracted light from the interference pattern of a standard microstructure

[0036] S4. Calculate the Fourier transform FT{A0(x1, y1)} of the standard microstructure. In order to obtain the Fourier transform of the standard microstructure corresponding to the diffraction or interference pattern collected by the CCD, the microstructure image used in the calculation process must have the same resolution as the interference or diffraction pattern, and ensure that the registration error between the Fourier transform result of the microstructure and the diffraction pattern in the horizontal and vertical directions is less than 1 pixel.

[0037] S5. Calculate the exponential phase factor C(x, y); exponential phase factor / FT{A0(x1, y1)}, where λ is the laser wavelength and f is the focal length of the biconvex lens. The exponential phase factor is only related to the experimental system and has nothing to do with the microstructure;

[0038] S6. Obtain the amplitude of the diffracted light from the diffraction pattern of the microstructure A(x1, y1) to be measured

[0039] S7. Obtain the phase of the diffracted light from the microstructure to be measured from the interference pattern

[0040] S8. Ratio of the diffraction complex amplitude to the exponential phase factor of the microstructure to be measured / C(x, y) performs inverse Fourier transform to restore the microstructure to be measured:

[0041]

[0042] Here, IFT{·} represents a two-dimensional inverse Fourier transform.

[0043] The method for obtaining the diffracted light phase of the standard microstructure and the microstructure to be measured in S3 and S7 is as follows: Taking the standard microstructure A0 (x1, y1) as an example, the interference pattern is inverse Fourier transformed to obtain the autocorrelation function of the spatially separated standard microstructure and reference light and the cross-correlation function of the two. or right Fourier transform gives Its phase is the phase difference between the two lights When the reference light is incident vertically on the CCD photosensitive surface, its phase is approximately constant. At this time, the phase of the diffracted light from the standard microstructure is Similarly, the phase of the diffracted light of the microstructure A(x1, y1) to be measured can be obtained

[0044] Example

[0045] This embodiment is an experimental example, and the device for generating the complex microstructure is a commonly used reflective amplitude modulator, a digital micromirror device DMD. Figure 1 (b) The experimental system is constructed. The coherent light source 1 is a helium-neon laser with a central wavelength of 632.8 nm. The coherent light emitted by the helium-neon laser passes through the polarizer 2 and the beam expansion and collimation system (double concave lens 3 and the first double convex lens 4), and then passes through the first beam splitter prism 5 to be divided into two paths of light. One path passes through the attenuation plate 6 and is reflected by the first reflector 7 to form a reference light, and the other path is reflected by the second reflector 8 and the third reflector 13 to reach the microstructure generating device 9 to form a diffracted light. After the diffracted light passes through the second double convex lens 10, it interferes with the reference light after being combined with the second beam splitter prism 11. The image-side focal plane of the second double convex lens 10 is shifted to a certain extent after passing through the second beam splitter prism 11. The photosensitive surface of CCD12 is placed on the image plane after the translation to collect the Fraunhofer diffraction pattern of the standard microstructure and the complex microstructure to be measured loaded on the DMD, as well as the interference pattern of the diffracted light and the reference light. The intensity of the diffracted light is relatively weak. In order to improve the visibility of the interference fringes, it is necessary to reduce the intensity of the reference light by adjusting the attenuation plate.

[0046] The parameters of other main instruments are as follows: the resolution of the DMD is 1920×1080, and the single-pixel size is 7.56μm×7.56μm; the focal length of the second double convex lens 10 is 100mm; the resolution of the CCD is 5496×3672, and the single-pixel size is 2.4μm×2.4μm. The standard microstructure and the microstructure to be measured loaded on the DMD are as Figure 3 shown, where the standard microstructure is a square hole of 60×60 pixels, and the complex microstructure to be measured is the Chinese character '中'.

[0047] The method for restoring the complex microstructure in this experiment is as follows:

[0048] S1. Collect Figure 3 the diffraction patterns and interference patterns of the standard microstructure and the microstructure to be measured shown as Figure 4 shown, and the size of the pictures is 400×400 pixels;

[0049] S2. Obtain the amplitude of the diffracted light of the standard microstructure from the diffraction pattern of the standard microstructure shown in Figure 4 (a);

[0050] S3. Obtain the phase of the diffracted light of the standard microstructure from the interference pattern of the standard microstructure shown in Figure 4 (b);

[0051] Perform an inverse Fourier transform on the interference pattern to obtain the autocorrelation function of the spatially separated standard microstructure and the reference light and the cross-correlation function of the two; or Perform a Fourier transform to obtain whose phase is the phase difference between the two beams of light; When the reference light is perpendicularly incident on the CCD photosensitive surface, its phase is approximately a constant; At this time, the phase of the diffracted light of the standard microstructure is

[0052] S4. Calculate Figure 3 the Fourier transform FT{A0(x1, y1)} of the standard microstructure shown in

[0053] In order to obtain the Fourier transform of the standard microstructure corresponding to the diffraction or interference pattern collected by the CCD, the picture containing the standard microstructure needs to be readjusted. While keeping the actual size of the standard microstructure unchanged, ensure that the microstructure picture used in the calculation process has the same resolution as the interference or diffraction pattern. In addition, translate the result after the Fourier transform of the microstructure to ensure that the registration error in the horizontal and vertical directions between it and the diffraction pattern is less than 1 pixel.

[0054] S5. According to the diffraction integral formula The exponential phase factor is calculated using the diffraction complex amplitude of the standard structure and the Fourier transform of the structure Where λ is the laser wavelength and f is the focal length of the biconvex lens. The exponential phase factor is only related to the experimental system and has nothing to do with the microstructure;

[0055] S6, from Figure 4 The amplitude of the diffracted light is obtained from the diffraction pattern of the microstructure A(x1, y1) to be measured shown in (c)

[0056] S7, from Figure 4 (d) The phase of the diffracted light of the structure is obtained from the interference pattern of the microstructure to be measured.

[0057] Perform inverse Fourier transform on the interference pattern to obtain the autocorrelation function and cross-correlation function of the spatially separated microstructure to be measured and reference light. or right Fourier transform gives Its phase is the phase difference between the two lights The phase of the reference beam is approximately constant Therefore, the phase of the diffracted light of the microstructure to be measured is

[0058] S8. According to the integral formula The ratio of the diffraction complex amplitude to the exponential phase factor of the microstructure to be measured Perform inverse Fourier transform to restore the microstructure to be measured:

[0059]

[0060] Here, IFT{·} represents a two-dimensional inverse Fourier transform.

[0061] According to the above steps, we get Figure 3 (b) The restoration results of the microstructure, such as Figure 5 As shown. It can be found that the restoration result not only reproduces the original microstructure well in terms of size and structure, but also eliminates the existence of zero-order spots and conjugate images. The restoration result was evaluated by using the structural similarity index SSIM, and the SSIM of the experimental result and the original structure reached more than 90%. Therefore, the application of the experimental system and restoration method in the present invention can realize the measurement of complex microstructure interference diffraction phenomenon and rapid and high-precision restoration.

Claims

1. A structural restoration method, characterized in that: The structure restoration method adopts a microstructure interference diffraction measurement device, which includes a coherent light source, a polarizer, a beam expansion and collimation system, a first beam splitter prism, an attenuation plate, a first reflector, a microstructure generating device, a second biconvex lens, a second beam splitter prism and a CCD. The light emitted by the coherent light source passes through the polarizer and the beam expansion and collimation system, and then passes through the first beam splitter prism to be divided into two paths of light. One path passes through the attenuation plate and is reflected by the first reflector to form a reference light, and the other path reaches the microstructure generating device to form a diffracted light. After the diffracted light passes through the second biconvex lens, it interferes with the reference light after being combined with the second beam splitter prism. The image side focal plane of the second biconvex lens is translated after passing through the second beam splitter prism, and the CCD photosensitive surface is placed on the translated image plane. The structure restoration method includes the following steps: S1. Use CCD to collect diffraction patterns of a standard microstructure A0 (x1, y1) with known size and a complex microstructure A (x1, y1) to be measured, as well as interference patterns of diffracted light and reference light; S2. Obtain the amplitude of the diffracted light from the diffraction pattern of the standard microstructure A0(x1,y1) S3. Obtaining the phase of diffracted light from the interference pattern of a standard microstructure S4, calculate the Fourier transform FT{A0(x1,y1)} of the standard microstructure; S5. Calculate the exponential phase factor C(x,y); S6. Obtain the amplitude of the diffracted light from the diffraction pattern of the microstructure A(x1,y1) to be measured S7. Obtain the phase of the diffracted light from the interference pattern of the microstructure to be measured S8. Ratio of the diffraction complex amplitude to the exponential phase factor of the microstructure to be measured Perform inverse Fourier transform to restore the microstructure to be measured.

2. The structural restoration method according to claim 1, characterized in that: The microstructure generating device adopts an amplitude or phase modulator, including a reflective amplitude or phase modulator and a transmissive amplitude or phase modulator.

3. The structural restoration method according to claim 2, characterized in that: When the microstructure generating device adopts a reflective amplitude or phase modulator, a third reflector and a second reflector are placed on the optical path in front of the microstructure generating device.

4. The structural restoration method according to claim 1, characterized in that: The second biconvex lens images the diffraction pattern on the image focal plane of the lens.

5. The structural restoration method according to claim 4, characterized in that: The second beam splitter prism causes the image plane of the diffraction pattern to shift, and the amount of shift Δl is related to the refractive index n and the thickness d of the second beam splitter prism, that is, Δl=d(1-1 / n).

6. The structural restoration method according to claim 1, characterized in that: The intensity of the reference light is reduced by adjusting the attenuation plate.

7. The structural restoration method according to claim 1, characterized in that: The microstructure image used in the calculation process of S4 has the same resolution as the interference or diffraction pattern, and the registration error between the Fourier transform result of the microstructure and the diffraction pattern in the horizontal and vertical directions is less than 1 pixel.

8. The structural restoration method according to claim 1, characterized in that: The exponential phase factor Where λ is the laser wavelength and f is the focal length of the biconvex lens.

9. The structural restoration method according to claim 1, characterized in that: The diffracted light phase of the standard microstructure is obtained as follows: the interference pattern of the standard microstructure is inversely Fourier transformed to obtain the autocorrelation function of the spatially separated standard microstructure and the reference light and the cross-correlation function of the two. or right Fourier transform gives Its phase is the phase difference between the two lights When the reference light is incident vertically on the CCD photosensitive surface, its phase is approximately constant. At this time, the phase of the diffracted light from the standard microstructure is The phase of the diffracted light of the microstructure A(x1,y1) to be measured

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