JP7786705B2 - Object shape measuring device and object shape measuring method - Google Patents

Description

The present invention relates to single pixel imaging that realizes high-precision, high-resolution, and high-speed imaging, and to an object shape measuring device that realizes object shape measurement and imaging using an image processing method.

A method using holographic recording media has been proposed as an imaging technology for target objects. It is known that a complex amplitude distribution, including the amplitude and phase distributions of the object light, can be recorded by irradiating a recording medium such as a holographic recording medium with interference light produced by the interference of object light and reference light. Because the phase distribution reflects information that depends on the refractive index of the object, recording media capable of recording complex amplitude distributions have the advantage of being able to directly record shape information of the object. In this regard, there is a device that detects the phase distribution of a target object (see Patent Document 1). This device determines whether or not there is a correlation with the target object based on whether the light intensity emitted from the holographic recording medium and detected by a photodetector exceeds a threshold value. However, determining the threshold value requires prior preparation, such as experiments, and it is difficult to obtain detailed information about the phase and amplitude distributions of the target object simply by obtaining a correlation based on light intensity.

Another technology is single-pixel imaging (SPI), hereafter referred to as SPI. This is a method of imaging a target object using a single-pixel photodetector with a single-pixel light receiving section. In this method, an optical system applies pattern information to the target object to encode the target object, and the encoded light is acquired by a single-pixel photodetector, and a reconstruction calculation is performed on a computer to obtain an image of the target object. This method is described in Patent Document 2, and the acquisition of complex amplitude images is described in Non-Patent Document 1. However, SPI has the problem of taking a long time to reconstruct the image because the encoded light must be acquired multiple times.

Patent Publication No. 2009-237085 Patent Publication No. 2021-100186

L. Martinez-Leon, P. Clemente, Y. Mori, V. Climent, J. Lancis, and E. Tajahuerce, “Single-pixel digital holography with phase-encoded illumination,” Opt. Express 25(5), 4975-4984 (2017).

In conventional technologies, for example, methods using holographic recording media required prior preparation such as experiments to determine the threshold value of the light intensity obtained by the photodetector, and it was difficult to obtain detailed information about the phase distribution and amplitude distribution of the target object from correlations obtained using light intensity.

Another method is SPI, which acquires an image of the target object by capturing encoded light from the target object using a single-pixel photodetector and performing reconstruction calculations on a computer.However, this method has the drawback of taking a long time to reconstruct the image because the encoded light must be captured multiple times.

As a means of solving the above problem, an object shape measurement device that applies SPI to achieve high-precision, high-speed imaging can be created by configuring an SPI using a hologram recording medium on which interference fringes generated in advance using a two-dimensional spatial light modulator that modulates the amplitude and/or phase of light using multiple pixels are recorded as a hologram, and a spatial filter with an aperture approximately the size of one pixel of the two-dimensional spatial light modulator.

According to the present invention, by acquiring the optical correlation intensity of one pixel, it is possible to acquire a complex amplitude image of the target object or diffracted from the target object, thereby providing three-dimensional information of the target object and quantitative phase information such as refractive index and thickness. Furthermore, by applying an optical correlator to the above-mentioned holographic recording medium, it is possible to acquire the correlation between the phase modulation pattern and the target object at high speed, thereby enabling the provision of a high-speed reconstructed image of the target object.
Furthermore, unlike conventional two-dimensional imaging devices, the spatial resolution depends on the phase modulation pattern, so by increasing the number of pixels per unit length of the phase modulation pattern used, it is possible to provide a highly accurate reconstructed image.

For these reasons, there is a high possibility that this technology will be applicable to object shape measurement devices that achieve high-precision, high-speed imaging not only with visible light, but also with wavelengths outside the visible range, such as X-rays and ultraviolet light, which have high energy levels and are difficult to increase the output to achieve high image quality, as well as terahertz light and short-wavelength infrared light, for which it is difficult to put two-dimensional image sensors to practical use.As a result, in the future it will be possible to provide object shape measurement devices that can evaluate cells, bacteria, and semiconductor microstructures.

1 is a diagram showing an example of an overall system configuration including an object shape measuring apparatus according to an embodiment; FIG. 2 is a software configuration diagram of the object shape measuring apparatus according to the embodiment. 1A and 1B are diagrams illustrating the principle of a measurement method that is a main technology of an object shape measurement apparatus according to an embodiment. 10A to 10C are diagrams showing a method for creating a hologram recording medium used in the object shape measuring apparatus according to the embodiment. 10A to 10C are diagrams showing a method of forming an object beam used in the object shape measuring apparatus according to the embodiment. 3A and 3B are diagrams showing an example of object light used in the object shape measuring apparatus according to the embodiment. 1A and 1B are diagrams showing an example of a Hadamard pattern used in an object shape measurement apparatus according to an embodiment. Flowchart for creating a hologram recording medium used in an object shape measuring apparatus according to an embodiment 4 is a flowchart of a measurement method of the object shape measurement apparatus according to the embodiment. 3 shows a specific recording optical system of the object shape measuring apparatus according to the embodiment. 1 shows a specific reproduction optical system of an object shape measuring apparatus according to an embodiment. FIG. 1 is a diagram showing the physical positions of specific optical system components of an object shape measurement apparatus according to an embodiment; 10 shows the amplitude distribution and phase distribution of a target object to be reconstructed to demonstrate the effectiveness of the object shape measurement apparatus according to the embodiment. 10 shows amplitude distribution and phase distribution of a reconstructed image for demonstrating the effectiveness of the object shape measurement apparatus according to the embodiment. FIG. 10 is a diagram showing a case where reconstruction processing is performed by hardware.

Embodiments of the present invention will be described below with reference to the drawings. Identical components throughout the drawings will be assigned the same reference numerals, and duplicate explanations will be omitted. In the following embodiments, an object shape measurement device according to the present invention will be used as an example for explanation.

Figure 1 is a diagram showing an example of the overall configuration including an object shape measurement apparatus 1 according to an embodiment of the present invention. In the object shape measurement apparatus 1 shown in Figure 1, the target object 4 is an example of a light-transmitting type, but this is not limited to this and a reflective type is also possible. This object shape measurement apparatus 1 is composed of two functional elements: an optical system 2 and a system control/processing function 10. Each function is described in detail below. In the optical system 2, light irradiated from a light source 3 emitting, for example, a single-wavelength green laser is incident on the target object 4. While a green laser is used in the above example, this is not limiting and a red or blue laser can also be used as long as it is a single wavelength. The light then passes through a first lens 5, a hologram recording medium 6, and a second lens 7, then passes through a spatial filter 8. The transmitted light is converted into an electrical signal by a photodetector 9 and input to a CPU 11. A detailed description of the functions, including the operation of the optical system 2, will be given later.

The system control and processing function 10 controls the operation of each of the above functions and performs calculation processing. It is composed of a CPU 11, ROM 12, RAM 13, external memory 14, and system bus 17. Other components include a drive unit 15 for driving the hologram recording medium 6 and a display unit 16 for displaying detailed images of the target object 4. The CPU 11 turns the power on and off for the light source 3 in the optical system 2, performs detailed control of the drive unit 15, sets various settings, controls the program for image processing calculations of the target object (described below), and sets various commands. The ROM 12 stores system software, processing calculation programs, and their initial values. The RAM 13 is a memory space for executing various software programs run by the CPU 11, or for recording data and settings temporarily recorded during calculations. The external memory 14 is a memory for retaining data that cannot be stored in the ROM 12 or RAM 13, as well as previous data. It can also be used to store software updates and new settings. Image data of the target object 4 processed and calculated by the CPU 11 (described below) is displayed on the display unit 16. These data are transmitted and received via the system bus 17. Although not shown in Fig. 1, the data may be transmitted and received externally via a network.
FIG. 2 is a diagram showing the software configuration of the object shape measuring device 1 of this embodiment, which is made up of a CPU 11, a ROM 12, a RAM 13, an external memory 14, and a system bus 17.

CPU 11 is a microprocessor unit that controls the entire object shape measurement device 1 according to a predetermined program. System bus 17 is a data communication path for sending and receiving data between CPU 11 and each part within the object shape measurement device 1.

ROM (Read Only Memory) 12 is memory that stores basic operating programs such as the operating system and other application programs. Rewritable ROM such as EEPROM (Electrically Erasable Programmable ROM) or flash ROM is used, and by updating the programs stored in ROM 12, it is possible to upgrade or expand the functionality of the basic operating programs and other application programs.

RAM (Random Access Memory) 13 serves as a work area when the basic operation program and other application programs are executed. Specifically, for example, basic operation program 12a stored in ROM 12 is expanded into RAM 13, and CPU 11 then executes the expanded basic operation program to form basic operation execution unit 13a. For simplicity's sake, the following description will be given assuming that the basic operation execution unit 13a controls each unit, as opposed to the process in which CPU 11 expands basic operation program 12a stored in ROM 12 into RAM 13 and executes it to control each unit. Similar descriptions will be used for other application programs.

The image processing execution unit 13b performs various software processes on the electrical signals converted from light intensity by the photodetector 9 to correct brightness and color, which are expressed as electrical signal levels, as well as edge processing, image quality improvement processing, and noise removal processing to make the electrically converted image clearer. The reconstruction calculation execution unit 13c will be described in more detail below. The setting value execution unit 13d for various components controls various setting values and sets initial values for the light source 3, the drive device 15 that drives the hologram recording medium 6, the photodetector 9, and the display unit 16. The image display execution unit 13e performs processing to display a detailed image of the target object 4 on the display unit 16 using the data calculated by the reconstruction calculation execution unit 13c, which will be described later. The temporary storage area 13f is an area for temporarily storing data during each of the above processes.

As shown in FIG. 2, the operation of the object shape measurement device 1 of this embodiment is controlled by the image processing execution unit 13b, reconstruction calculation execution unit 13c, various component setting value execution unit 13d, and image display execution unit 13e, which are executed by the CPU 11, after the image processing program 14b, reconstruction calculation execution unit 14c, various component setting value execution unit 13d, and image display execution unit 13e are mainly stored in the external memory 14. The various information/data storage area 14a is an area for storing the initial values of various functions, etc. The image processing execution unit 13b, reconstruction calculation execution unit 13c, various component setting value execution unit 13d, and image display execution unit 13e may be performed in part or in whole by hardware blocks that realize the operations of the image processing execution unit 13b, reconstruction calculation execution unit 13c, various component setting value execution unit 13d, and image display execution unit 13e.

ROM 12 and RAM 13 may be integrated with CPU 11. ROM 12 may also use a portion of the storage area within external memory 14, rather than being an independent configuration as shown in Figure 2. RAM 13 also has a temporary storage area for temporarily storing data as needed when various application programs are executed.

The external memory 14 may temporarily store information detected by the photodetector 9. It may also store various operational setting values for the object shape measuring device 1, positional information and various other information for the object shape measuring device 1, some or all of the data such as images and information captured by the object shape measuring device 1, and other programs.

A portion of the external memory 14 may replace all or part of the functions of the ROM 12. Furthermore, the external memory 14 needs to retain the stored information even when power is not supplied to the object shape measurement device 1. Therefore, devices such as flash ROM, SSD (Solid State Drive), and HDD (Hard Disc Drive) are used.

Next, we will explain the basic technology of this invention using mathematical formulas.

The optical system 2, including its operation, will be explained using Figure 3. The optical system 2 is composed of a light source 3 emitting a single wavelength, a target object 4, a first lens 5, a hologram recording medium 6 on which the intensity of the interference between the phase modulation pattern and the reference light (a hologram) is recorded, a second lens 7, a spatial filter 8, and a photodetector 9. This configuration is essentially the same as optical correlation single-pixel imaging (SPI). Hereinafter, the optical system 2 will be referred to as optical correlation SPI. As shown in Figure 3, the target object 4, hologram recording medium 6, spatial filter 8, and photodetector 9 are positioned at the focal length f of the first lens 5 and the second lens 7, respectively, forming a 4f optical system. The flow of the optical system 2 (optical correlation SPI) in the object shape measurement device 1 of Figure 1 will be explained using Figure 3. The single-wavelength light emitted from the light source 3, which irradiates light of a single wavelength such as a laser, is phase-modulated depending on the refractive index distribution of the target object 4 as it passes through the target object 4. By passing this phase-modulated single-wavelength light through a hologram recording medium 6 on which a hologram is recorded, diffracted light is emitted from the hologram recording medium 6 as a correlation between the target object 4 and the phase modulation pattern. This diffracted light is finally passed through a spatial filter 8 with a pinhole at an appropriate position, and the intensity of the diffracted light is acquired by a photodetector 9. The acquired light intensity is used to perform reconstruction calculations on a system control and processing function 10, making it possible to acquire a complex amplitude image of the target object 4.

Here, we will explain the three processes that are actually performed in optical system 2 (optical correlation SPI): the hologram recording process, correlation process, and reconstruction process.

The recording process involves recording the intensity of interference between the phase modulation pattern and the reference light as a hologram on the hologram recording medium 6. The principles for recording a hologram on the hologram recording medium 6 will be explained using FIG. 4 . The hologram recording process involves a second light source 20 emitting a single wavelength, such as a laser, similar to the light source 3 in FIG. 3 , the reference light emitted therefrom, a spatial light modulator 22 capable of modulating phase and amplitude, an object light having the same wavelength as the second light source 20 emitted from a third light source 21 emitting a single wavelength, such as a laser, similar to the light source 3, a third lens 23, and a recording medium 24 on which no hologram is recorded. As is clear from FIG. 4 , the spatial light modulator 22 and the recording medium 24 on which no hologram is recorded are located at the focal length f of the third lens 23. Next, the hologram recording process in FIG. 4 will be explained. First, the spatial light modulator 22 displays a phase modulation pattern _pn and a reference phase pattern a, which is reference light for establishing a reference phase for the phase modulation pattern. A phase shift ^ejφ is applied to the phase modulation pattern, where e is Napier's constant and j is the imaginary unit. An example of a phase modulation pattern and an example of a reference phase pattern are shown in FIG.

Single-wavelength light emitted from the third light source 21 is passed through the spatial light modulator 22, on which this phase-shifted phase modulation pattern and reference phase pattern are displayed, and phase-modulated. A specific example is shown in Figure 5. The spatial light modulator 22 displays a phase modulation pattern (Figure 5(a)) and a reference phase pattern (Figure 5(b)), which is reference light for setting the reference phase of the phase modulation pattern. Single-wavelength light emitted from the light source is passed through the spatial light modulator, on which this phase-shifted phase modulation pattern and reference phase pattern are displayed, and phase-modulated (Figure 5(c)). The phase-modulated light is called object light u, and is described by the following equation:

An example of this object light is shown in Figure 6. Figure 6 shows an amplitude distribution of the object light of 64x64 pixels and a phase distribution of the object light of 16x16 pixels. However, this number of pixels can be increased if higher precision is desired, and is shown as an example.

Next, the reference light r and the object light are made to interfere with each other, focused to a single point using a lens, and recorded as a hologram on the recording medium. The reference light is emitted from a second light source 20, preferably a point light source. The recorded hologram I is described by the following equation:

Here, when F is the Fourier transform, U = F[u] and R = F[r]. * is the complex conjugate. This recording process is performed by applying a phase shift to all phase modulation patterns. Specifically, a Hadamard pattern like the one shown in Figure 7 is recorded as a hologram on the recording medium. For example, in the case of Figure 6, the Hadamard pattern has a size of 16 x 16 pixels, resulting in a total of 16 x 16 = 256 Hadamard patterns. If four phase shifts, φ = 0, π/2, π, and 3π/2, are recorded, 16 x 16 x 4 = 1,024 holograms are recorded on the recording medium. To record the hologram at a new position, the drive unit 15 is used to move the hologram to the specified position while recording. During this recording process, sufficient time is required to record (fix) the hologram on the recording medium. This movement control is accurately performed using the system control and processing function 10. By repeating this process, the hologram recording medium 6 described above is created. A flowchart of the above recording process is shown in Figure 8. In the recording device shown in FIG. 4 for recording a hologram on the recording medium 24, the spatial light modulator 22 displays the phase modulation pattern and reference phase pattern shown in FIG. 5 (S101). A phase shift is applied to the displayed phase modulation pattern (S102). In this case, for example, φ=0, π/2, π, or 3π/2 is applied. As will be described later, four cases are shown: φ=0, π/2, π, and 3π/2. Next, a single-wavelength light is emitted from the light source 21 (S103). The wavelength used for recording a hologram on the recording medium 24 is selected based on the wavelength to which the recording medium 24 is sensitive. Next, a single-wavelength light is emitted from the light source 20 as a reference light (S104). This wavelength is the same as that of the light source 21 described in S103. Next, the light emitted from the light source 21 is used as an object light and phase-modulated by the spatial light modulator 22 according to Equation (1) (S105). Next, the interference light between the object beam and the reference beam is focused by the third lens 23 (S106), and the interference light is recorded as a hologram on the recording medium 24 (S107). After the hologram is recorded on the recording medium 24, the drive unit 15 moves the recording medium 24 to a predetermined position for recording the next hologram (S108). This movement control is performed by the system control and processing function. Steps S101 to S108 represent the recording process of one hologram. In other words, a hologram with a phase shift of φ=0 has been recorded. Next, a shift of, for example, φ=π/2 is applied (S109). In the above example, four phase shifts, φ=0, π/2, π, and 3π/2, are applied. In S110, a determination is made as to whether all phase shifts have been applied. If all phase shifts have been applied, proceed to S111. If not, repeat steps S102 to S109. After the four phase shifts described above have been applied, the next recording pattern is applied (S111). Finally, in step S112, it is determined whether all recording patterns have been recorded as holograms. In the case of Fig. 6, the size of the Hadamard pattern is 16 x 16 pixels, so 16 x 16 = 256 holograms are recorded, and therefore it is determined in step S112 whether all 256 Hadamard patterns have been recorded.

Next, the correlation process will be explained. The correlation process follows the flowchart shown in Figure 9. The following explanation will be made using Figure 9. Light of a single wavelength is emitted from the light source 3 (S201). As mentioned above, this light is phase-modulated depending on the refractive index distribution of the target object 4 (S202). If this phase-modulated light is designated as o, and the region of the target object 4 to be imaged is designated as o _t and the other regions are designated as o _o , then o can be described by the following equation:

The light o phase-modulated by the target object 4 is passed through a first lens 5 to be focused (S203). The light focused by the first lens 5 is then passed through a hologram recording medium 6 on which the above-mentioned hologram is recorded (S204), and the diffracted light is emitted from the hologram recording medium 6 (S205). When O=F[o], the diffracted light D immediately after emitting from the hologram recording medium 6 is described by the following equation.

In particular, among the diffracted light, the first term on the right-hand side is called 0th-order light, the second term is called 1st-order light, and the third term is called -1st-order light. This diffracted light is passed through the second lens 7 to make it parallel (S206), and only the 1st-order light or the -1st-order light is passed through the spatial filter 8 (S207). A pinhole is installed in the spatial filter 8 that passes the light. It is desirable to make the size of the pinhole as small as possible. When _{P n} = F[p _n ], A = F[a], and F ^-1 is the inverse Fourier transform, the 1st-order light d that has passed through the filter can be described by the following equation.

In particular, P _n *O in equation (5) corresponds to the correlation between the phase modulation pattern and the target object 4. Finally, this first-order diffracted light is acquired as intensity by the photodetector 9 (S208). In the above-described embodiment, the flowchart does not specifically describe how the light intensity is acquired when the phase shift amount is changed. However, in the above-described embodiment, four phase shift amounts, φ=0, π/2, π, and 3π/2, are applied, and therefore, the light intensity for all four phase shift amounts is acquired. A determination is made in S209 as to whether all four light intensities have been acquired. Furthermore, as described in FIG. 8 , in the above-described embodiment, 256 x 4 = 1,024 holograms are recorded on the hologram recording medium 6, and therefore, a determination is made in S210 as to whether the light intensity for all patterns has been acquired. Although not described here, each hologram is reproduced by high-speed position control using the drive unit 15. For example, to obtain a reconstructed image of the target object 4 in one second, the above-mentioned 1,024 holograms must be reconstructed in at least one second, meaning that one hologram must be reconstructed in 1/1,024 = approximately 977 microseconds. However, at this speed, if the recording medium were, for example, in the form of a disk and rotated at high speed, it could be reconstructed without any problems. The reconstruction calculation also needs to be completed in at least 977 microseconds, but this is not a problem given the processing power of the CPU.

Finally, the reconstruction process is shown. In the reconstruction process, the system control and processing function 10 performs reconstruction calculations based on the light intensity obtained by the photodetector 9. The phase modulation pattern can be phase shifted multiple times to obtain the corresponding light intensity; here, four phase shifts (φ=0, π/2, π, 3π/2) are performed. When the light intensities obtained for each phase shift are I _n,0 , I _n,π/2 , I _n,π , and I _n,3π/2, the reconstructed image o _recon is described by the following equation:

The process for carrying out this reconstruction calculation is S211, and the calculation is carried out by the system control and processing function 10 in FIG.
Here, the reconstructed image o _recon in the above equation (6) is a complex amplitude image, and it is also possible to obtain a three-dimensional reconstructed image by performing Fresnel propagation calculations on this complex amplitude distribution (multiple complex amplitude images). In this case, a detailed three-dimensional image of the target object can be obtained by increasing the number of complex amplitude images (increasing the number of holograms), which makes it possible to use it for various applications such as three-dimensional microscopes.

The results of an investigation conducted to clarify the effects of the above-described embodiment are presented below. The optical systems in Figures 10, 11, and 12 are shown as examples of embodiments, and the method will be explained using these figures. Figure 10 shows the optical system used during recording. During recording, light emitted from the light source (laser) 3 passes through the shutter 41, the half-wave plate 36, two mirrors M, a polarizing beam splitter (PBS) 35, and a beam expander (BE) 34, is narrowed by the aperture 37, reflected by the half-wave plate 36 and mirror M 32, passes through 32, and is reflected by the non-polarizing beam splitter (NPBS) 38 before entering the spatial light modulator (SLM) 22. Here, the spatial light modulator 22 simultaneously displays a pattern that will become the object beam and a pattern that will become the reference beam. 4 shows that the reference light and object light are irradiated from two light sources (second light source 20 and third light source 21) with the same wavelength, and the object light pattern is created by spatial light modulator 22, but in Fig. 10, one light source 3 enters spatial light modulator 22, and a point light source that becomes the object light pattern and reference light is irradiated from spatial light modulator 22. The light then passes through a non-polarizing beam splitter (NPBS) 38 and each optical component shown in Fig. 10, which is omitted below, before being irradiated onto the hologram recording medium and recording a hologram. Fig. 11 shows the optical system used during reconstruction. During reproduction, light emitted from light source (laser) 3 passes through shutter 41, half-wave plate 36, two mirrors M, polarizing beam splitter (PBS) 35, and beam expander (BE) 34, is narrowed by aperture 37, reflected by half-wave plate 36 and mirror M 32, passes through aperture 32, and is reflected by non-polarizing beam splitter (NPBS) 38 before entering spatial light modulator (SLM) 22. Here, the spatial light modulator 22 displays a pattern of the target object, and light is irradiated from the spatial light modulator 22 as the target object. Light passes through non-polarizing beam splitter (NPBS) 38 and various optical components shown in FIG. 11, which are omitted below, before being irradiated onto the holographic recording medium. The irradiated target object light and diffracted light from the holographic recording medium on which a hologram has been recorded pass through or are reflected by various optical components shown in FIG. 11, which are omitted below, pass through pinhole 39, and enter photomultiplier tube (PMT) 40. The dotted line represents the first-order diffracted light returning from the hologram disc. It is distinguished from the zeroth-order diffracted light (solid line) entering the optical amplifier tube 40. This pinhole 39 corresponds to the spatial filter 8 shown in Figure 3, and the photomultiplier tube 40 corresponds to the photodetector 9 shown in Figure 3. A key feature of this invention is that the object light pattern to be recorded on the hologram recording medium is created and displayed using the spatial light modulator 22, and the pinhole-type spatial filter 8 is placed in front of the photodetector 9. This enables accurate acquisition of phase and amplitude information of the target object. Figure 12 shows the relationship between the arrangement of each optical component, the focal length f, and the Fourier plane. In this figure, the symbols used to explain each optical component have been omitted to clarify the relative positions of the components. The focal lengths f of the lenses 31 in Figures 10 and 11 are as shown in Figure 12, and each component is positioned at the focal length shown in Figure 12. The relationship between the position of each component and the Fourier plane is also shown in Figure 12.

Next, Figures 13 and 14 show the results of a simple simulation of the amplitude and phase distributions of the object to be reconstructed, and the amplitude and phase distributions of the reconstructed image. In the simulation, the reference light was used as a point light source and expressed as a Gaussian distribution. Taking into account the full width at half maximum of this Gaussian distribution and the size of the pinhole opening of the spatial filter that only passes first-order light, the reconstructed image when the full width at half maximum was 1 pixel and the pinhole size was 1 x 1 pixel was referenced. Evaluation was also performed using RMSE. A smaller RMSE value indicates higher accuracy of reconstruction. The RMSE for the amplitude distribution was 0.07613, and the RMSE for the phase distribution was 0.00979, confirming high accuracy of reconstruction.

The above shows various experimental results, study results, sample shapes, etc., quantified to explain the effects of the present invention, but the above quantification is merely an example, and various shapes can be used depending on the size and shape of the target object.

In the above description, the process of actually acquiring light intensity and performing reconstruction calculations based on that data is described in FIG. 2 as being performed by software within the system control and processing function 10 in FIG. 1 . However, for example, part or all of the recalculation processing unit, as shown in FIG. 15 , may be configured with hardware. In FIG. 15 , various processes are performed on the electrical signals converted from light intensity by the photodetector 9. That is, image processing 42 corrects the brightness and color expressed as the electrical signal level, performs edge processing, image quality improvement processing, and noise reduction processing to make the converted image clearer, and converts the data into appropriate data values. Reconstruction calculation 43 is then performed, followed by image display processing 44 to display an image of the target object 4. While the above description describes a case where 1,024 holograms are recorded on a holographic recording medium, there are cases where more holograms are recorded on a recording medium for higher accuracy and speed. Therefore, the reconstruction calculation unit may be configured with hardware to significantly improve processing speed.

1: Object shape measuring device, 2: Optical system, 3: Light source (laser), 4: Target object, 5: First lens, 6: Hologram recording medium, 7: Second lens, 8: Spatial filter, 9: Photodetector, 10: System control and processing function, 11: CPU, 12: ROM, 13: RAM, 14: External memory, 15: Drive device, 16: Display unit, 17: System bus, 20: Second light source, 21: Third light source, 22: Spatial light modulator (SLM), 23: Third lens, 24: recording medium without hologram recorded, 31: lens L, 32: mirror M, 33: objective lens, 34: beam expander (BE), 35: polarizing beam splitter (PBS), 36: half-wave plate (HWP), 37: aperture, 38: non-polarizing beam splitter (NPBS), 39: pinhole, 40: photomultiplier tube (PMT), 41: shutter, 42: image processing, 43: reconstruction calculation, 44: image display processing

Claims (4)

a first optical element that converges parallel light of a single wavelength that is emitted from a light source and incident on a target object and that is transmitted through or reflected by the target object;
a recording medium that is arranged at a focal position of the first optical element, and diffracts and outputs light converged by the first optical element using a hologram in which interference fringes of a plurality of modulation patterns in which the modulation states of the unit modulation elements are different from each other are arranged, the interference fringes being interference fringes of a reference light and object light modulated by a two-dimensional spatial light modulation unit in which unit modulation elements are arranged two-dimensionally ;
a second optical element that converges the light emitted from the recording medium;
a third optical element that is disposed at a focal length of the second optical element, has an aperture having a size equal to the size of the unit modulation element of the two-dimensional spatial light modulation unit, and transmits primary light of the light converged by the second optical element through the aperture ;
a light detection unit that detects the intensity of light transmitted through the third optical element ;
An object shape measuring device comprising : the modulation patterns include a first phase modulation pattern having a first phase difference from a reference phase pattern, and a second phase modulation pattern having a second phase difference from the first phase modulation pattern that is different from the phase difference from the reference phase pattern,
In the hologram, the interference fringes are arranged at first positions where the interference fringes of the first phase modulation pattern are arranged, and at second positions where the interference fringes of the second phase modulation pattern are arranged.
The object shape measuring device according to claim 1 . a reconstruction unit that calculates a complex value including a correlation between a signal pattern and the target object based on the intensity of the light detected by the light detection unit, and reconstructs a complex amplitude image of the target object based on the calculated complex value ;
a display control unit that displays a three-dimensional object by performing light propagation calculation on the reconstructed complex amplitude image;
The object shape measuring apparatus according to claim 1 , further comprising: A single-wavelength parallel light beam emitted from a light source and incident on a target object is transmitted through or reflected by the target object and converged by a first optical element;
A recording medium is arranged at a focal position of the first optical element, and the light converged by the first optical element is diffracted and emitted by a recording medium that is a hologram on which interference fringes of a plurality of modulation patterns, which are interference fringes of a reference light and an object light modulated by a two-dimensional spatial light modulation unit in which unit modulation elements are arranged two-dimensionally, and in which modulation states of the unit modulation elements are different from each other, are arranged.
converging the light emitted from the recording medium by a second optical element;
a third optical element that is arranged at a focal length of the second optical element, has an aperture having a size equal to the size of the unit modulation element of the two-dimensional spatial light modulation unit, and transmits primary light of the light converged by the second optical element through the third optical element having the aperture;
detecting the intensity of the light transmitted through the third optical element by a light detection unit;
An object shape measurement method comprising: