Anti-vibration method of single-frame quantitative phase imaging interferometer

Abstract

The invention provides an anti-vibration method of a single-frame quantitative phase imaging interferometer. An optical interference measurement technology has extremely high precision and sensitivity, measurement misalignment can be caused by fine vibration, and in a long-time continuous image acquisition process, vibration in an interference light path is often a problem which is difficult to solve. The invention provides an anti-vibration method of a single-frame quantitative phase imaging interferometer, which comprises the following steps: firstly, introducing a proper spherical phase into an object light path part in an interference light path, then carrying out unwrapping processing on the obtained phase, and finally, eliminating the spherical phase through an algorithm, so that the influence of vibration on the interference light path is effectively reduced, and the anti-vibration performance of the interference light path is improved. And stable and continuous quantitative phase imaging is ensured. The method is suitable for single-frame quantitative phase imaging equipment and has good application prospects in various fields.

Description

Technical Field

[0001] The invention relates to the field of phase-shift interference anti-vibration, in particular to an anti-vibration method for a single-frame quantitative phase imaging interferometer. Background Art

[0002] Phase-shift interferometry is a highly sensitive non-contact optical measurement method, which is widely used in the fields of optical surface measurement and deformation measurement. However, environmental vibration is one of the main factors affecting the measurement accuracy of this technology, including fringe jitter, interference image blur and other phenomena. At present, there are some solutions, which can be divided into two categories according to the working mode: passive anti-vibration technology and active anti-vibration technology.

[0003] Among passive vibration-proof technologies, the most widely studied one is the vibration-proof method in time-domain phase shifting, which is to calculate the phase distribution that excludes the influence of vibration from the multi-frame phase-shifted interference graphs containing vibration information collected at different times; the second type is the single-frame interference graph processing technology, which naturally avoids the influence of vibration because only one interference graph is used for processing; the third type is the spatial domain phase shifting technology, which collects a group of phase-shifted interference graphs at the same time, thus avoiding the influence of vibration and using conventional phase shifting algorithms for calculation. Active vibration-proof technology aims to weaken the propagation of environmental vibration, so it mainly uses external equipment such as air-floating platforms and shields for vibration-proofing.

[0004] At present, the existing phase-shift interferometric anti-vibration technology has the following shortcomings:

[0005] 1. Some anti-vibration technologies may require special hardware support, such as high-speed response photodetectors, piezoelectric ceramic (PZT) drivers, etc., which may increase the complexity and cost of the system.

[0006] 2. In practical applications, the stability and reliability of the system are crucial to anti-vibration performance, but existing technologies may still face challenges in long-term operation or changing environments.

[0007] 3. In some dynamic measurements that require fast response, existing anti-vibration technology may not meet real-time requirements, especially when dealing with high-frequency vibrations. Summary of the invention

[0008] The purpose of the present invention is to provide a single-frame quantitative phase imaging interferometer anti-vibration method, which can effectively reduce the impact of interference light path vibration on the results, ensure stable and continuous quantitative phase imaging, and can be performed in real time without the need for additional equipment.

[0009] The present invention is achieved in that:

[0010] The present invention provides an anti-vibration method for a single-frame quantitative phase imaging interferometer. First, a spherical phase with a phase size of 4π to 8π is introduced into the object light path part of the interference light path, and then the obtained phase is unwrapped. Finally, the spherical phase is eliminated through an algorithm, thereby effectively reducing the impact of vibration on it and ensuring stable and continuous quantitative phase imaging. The method is applicable to single-frame quantitative phase imaging equipment and has good application prospects in various fields.

[0011] Preferably, the introduced spherical phase is about 6π.

[0012] The anti-vibration method of the above-mentioned single-frame quantitative phase imaging interferometer specifically comprises the following steps:

[0013] S1. First, a spherical phase is introduced into the object light path part in the interference light path, and the spherical phase is larger than the vibration phase caused by the vibration;

[0014] S2. A single-frame image is collected by a polarization camera, and four polarization phase shift images are extracted. The phase shift caused by vibration is a global shift. The light intensity corresponding to the four polarization phase shift images is expressed as follows:

[0015]

[0016] In formula (1), I0(x,y,z) and ΔI(x,y,z) represent the background light and the detection light respectively; Indicates the phase to be measured;

[0017]

[0018] in, represents the sample phase, represents the spherical phase, Indicates the vibration phase;

[0019] By performing addition and subtraction operations on formula (1), we can obtain:

[0020]

[0021] Then perform the inverse tangent operation to obtain the phase value to be measured

[0022]

[0023] S3, the obtained phase Perform unwrapping processing, that is, use the fast cosine least squares unwrapping algorithm to unwrap the phase;

[0024] S4. Subtract the spherical phase from the unfolded phase to obtain the phase of the sample.

[0025] The present invention does not need to provide complex hardware equipment, and can significantly reduce the influence of vibration by only introducing a spherical phase and combining a fast and stable fast cosine least squares unwrapping algorithm.

[0026] The present invention has the following advantages due to the adoption of the above technical solution:

[0027] 1. Reduce the impact of vibration by unpacking, without adding hardware equipment, reducing the complexity and cost of the optical path, and having the characteristics of fast and stable.

[0028] 2. This technology is suitable for single-frame quantitative phase imaging equipment and provides a new solution for anti-vibration technology in optical interferometry.

[0029] 3. This technology can realize rapid real-time recording of Paramecium phase images, and can quantitatively analyze the characteristics of Paramecium's three-dimensional morphology. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the anti-vibration process provided by the present invention; in the figure, (1) is the introduced spherical phase; (2) is the phase jitter caused by vibration; (3) is the wrapped phase; (4) is the phase after unwrapping; and (5) is the object phase after recovery.

[0031] Figure 2 1 is a simulation process diagram in an embodiment of the present invention; wherein (a) is the original phase image, (b) is the unwrapped phase image, and (c) is the restored phase image.

[0032] Figure 3 This is a Mach-Zehnder optical path diagram constructed in an embodiment of the present invention; in the figure, He-Laser: 632.8nm helium-neon laser; HWP: half-wave plate; F1, F2, F3, F4: lenses; PBS1, PBS2: polarization beam splitters; M1~M6: reflectors; OL: objective lens; QWP: 1 / 4 wave plate.

[0033] Figure 4 These are the experimental diagrams of the unwrapped phase during the vibration process; among them, (a) is the original phase diagram, (b) is the unwrapped phase diagram, and (c) is the restored phase diagram.

[0034] Figure 5 The vibration phase changes of Paramecium are collected continuously for 10 seconds. (a) is the initial phase image of the first frame in the Paramecium phase image collected continuously for 10 seconds. (b) is the comparison diagram of the vibration phase changes within 10 seconds. DETAILED DESCRIPTION

[0035] In order to solve the problem of existing phase shift interference vibration, this embodiment provides a single-frame quantitative phase imaging interferometer anti-vibration method. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0036] For a certain phase position, if there is no vibration during the acquisition process, normal interference images can be continuously acquired, and their light intensity information should remain consistent. When there is a vibration effect, the acquired interference image will undergo complex movements such as translation, deflection, extension and zoom. Since the time required for a high frame rate camera to acquire a frame of image is approximately in milliseconds, the relative movement between the interference images caused by vibration is mainly translation, and other forms of movement have little effect. In the process of dynamic image acquisition, each frame of the image is affected by vibration, but the shape and position of the interference ring between adjacent frames are basically unchanged, only the number of apertures is changing, and the interference ring emerges from the center or shrinks to the center due to vibration. Therefore, this shows that the vibration causes a relative offset in the z direction between the frames of the image, and has no effect on the x and y directions, such as Figure 1 As shown in (2). The camera used can extract four polarization phase shift images from one frame of image. In this process, the influence of vibration on each pixel is consistent, that is, the phase shift caused by vibration is globally consistent. The present invention introduces a spherical phase of about 6π, such as Figure 1 As shown in (1), the overall phase is unwrapped, as Figure 1 As shown in (4), the error caused by vibration is reduced during the unpacking process, such as Figure 1 As shown in (5).

[0037] In phase-shift interferometry, the intensity of the superimposed light field can be expressed as:

[0038]

[0039] Where n = 1, 2, 3 .... N, N is the number of phase shift steps, I0 (x, y, z) and ΔI (x, y, z) represent the intensity of background light and detection light respectively. is the overall phase, δ n Indicates the phase shift amount.

[0040] A single frame image captured by a polarization camera can extract four polarization phase shift images, and the phase shift δ n are 0, π / 2, π, and 3π / 2 respectively. In this process, the phase shift caused by vibration is a global shift. n Substituting into formula (1) and using the trigonometric function induced formula, we can obtain:

[0041]

[0042] By operating the above formula, we can get:

[0043]

[0044] Then perform the inverse tangent operation to obtain the phase value to be measured:

[0045]

[0046] The phase value obtained Include object phase The introduced spherical phase is about 6π and vibration phase can be written as:

[0047]

[0048] Due to the existence of the vibration phase, obvious phase jitter will occur, resulting in inaccurate phase values. During the acquisition process of the polarization camera, pixels of different polarization directions of the micro-polarization array are acquired simultaneously, and the vibration influence on each pixel is consistent, that is, the same vibration phase is added to each pixel, forming a global phase offset. Since phase unwrapping is achieved by calculating the phase difference between adjacent pixels, if all pixels are added with the same phase offset, then this offset will not change the phase difference between any two adjacent pixels. Therefore, although the absolute phase value of each pixel has changed, the phase change (that is, the phase gradient) remains unchanged. That is, the minimum phase value is fixed through the unwrapping algorithm to eliminate the vibration phase. Subtract the introduced spherical phase So as to obtain the object phase

[0049] According to the analysis of vibration, vibration can be considered as a very small random phase. A random phase is loaded in the object light path to simulate the vibration process. First, a reference light and a probe light are constructed. The reference light is a plane wave, and the probe light is a spherical wave. The interference obtains a hologram. Then, a random phase caused by vibration and the phase of the object itself are added to the object light, and then interfered with the reference light. Finally, the acquisition process of each frame of the image is simulated in a loop. The simulation results are as follows: Figure 2 shown. Figure 2 In the figure, (a) is the original phase image, (b) is the unwrapped phase image, and (c) is the restored phase image. Figure 2 It can be seen that there is basically no phase jitter after unwrapping. At this time, subtracting the fitted spherical surface can get a flat background, and the phase of the corresponding object can also be obtained.

[0050] The method of the present invention has not only been verified from the simulation aspect, but also a real-time observation experiment of Paramecium was carried out using a Mach-Zehnder interference optical path built in the laboratory, further demonstrating the feasibility of the method.

[0051] In order to more intuitively reflect the anti-vibration effect, the following Figure 3 The Mach-Zehnder interferometer optical path shown in the figure is used to perform phase imaging on the Paramecium specimen. Figure 3 As shown, the light source uses a 632.8nm helium-neon laser. The laser passes through lenses F1 and F2 for collimation and beam expansion, and then passes through a polarization beam splitter PBS to obtain two mutually orthogonal polarized lights, one of which is P polarized light (horizontally polarized - x-axis) and the other is S polarized light (vertically polarized - y-axis). The half-wave plate (HWP in the figure) can be used to change the splitting ratio of the reference light and the detection light to obtain the best interference image. One of the reflected vertically polarized lights is used as the reference beam, and the other transmitted horizontally polarized light is used as the detection light, so that it carries the phase information of the target object. The detection light passes through mirrors M1, M2, and M3 in turn, so that the light beam passes through lens F3 to increase the light field density, and then passes through a horizontally placed sample to make the reference light and the detection light field intensity consistent. The light beam carrying the object information is collected by the objective lens OL (magnification is 16 times, NA=0.4), and finally enters the polarization beam splitter PBS2 through the reflector M4 and lens F4, and is combined with the reference light to obtain a superimposed field. The two fields are then transmitted to circularly polarized light with opposite hand directions through a 1 / 4 wave plate (QWP in the figure), and then collected by a polarization camera (Pol-CC in the figure). The micro-polarization array on the polarization camera is repeatedly arranged in units of 2×2, which are 0°, 45°, 90° and 135° respectively. A single captured image contains four polarization direction distributions. By performing pixel operations on the light intensity images of four different polarization directions, a single measurement of phase shift images with different polarization angles can be achieved. Finally, four polarization images can be obtained, and the Paramecium phase image can be obtained through algorithms such as anti-vibration and phase recovery. The experimental results are shown in the figure. Figure 4 shown. Figure 4 In the figure, (a) is the original phase image, (b) is the unwrapped phase image, and (c) is the restored phase image. Figure 4 (a) It can be observed intuitively that each original phase image is affected by vibration. The interference ring remains basically unchanged in the x and y directions, but is disturbed in the z direction, causing the interference ring to emerge or shrink from the center. That is, the vibration causes a relative translation in the z direction between each frame image. Figure 4 As can be seen in (b), the phase values ​​of each frame image are basically the same after unwrapping, which obviously reduces the impact of vibration and verifies the feasibility of this method. This method does not require additional hardware equipment and can be performed quickly and stably for a long time.

[0052] Phase imaging of Paramecium was performed, and the data were collected continuously for 10 seconds. The results of the vibration phase change of Paramecium are as follows: Figure 5 shown. Figure 5 In the figure, (a) is the initial phase image of the first frame in the continuous acquisition of 10s of the paramecium phase image; (b) is a comparison of the vibration phase changes within 10s. In order to intuitively reflect the anti-vibration effect, the average phase value of 50 pixels in the first frame of all the collected phase images (the starting coordinates are (110,450) and the ending coordinates are (115,460)) is taken as the first basic phase value. Every 0.5s, the phase value of each pixel in the same area as the first frame of the phase image is taken and the difference is made with the first basic phase value, and then the average is taken to obtain the vibration phase. The standard deviation is used as an error bar to represent the phase fluctuation. Ideally, the average value is equal in all the collected phase images, but the phase value will fluctuate due to the influence of vibration. Figure 5 The two lines in (b) respectively show the changes in the vibration phase value before and after anti-vibration using the method of the present invention. The dotted line is the phase change curve before anti-vibration, and the solid line is the phase change curve after anti-vibration. It can be clearly seen that before anti-vibration, the vibration phase fluctuates significantly due to jitter, and the phase value is erratic. This phenomenon becomes more obvious as time goes by. After anti-vibration, the fluctuation of the phase value is significantly reduced, and the phase value is stable, indicating that this method can significantly suppress the error caused by vibration.

[0053] The present invention first analyzes the vibration and concludes that the phase shift caused by vibration is globally consistent, and the vibration causes a relative shift in the z direction between each frame image, and has no effect on the x and y directions. Then, an appropriate spherical phase is introduced to wrap the phase in the range of [-π,π], and the phase is unfolded using a fast cosine least squares unwrapping algorithm to suppress vibration errors. The above process is then simulated and verified using Matlab software. Finally, the Paramecium specimen is imaged using the constructed Mach-Zehnder optical path, and four polarization images are finally obtained, and the Paramecium phase image is obtained through algorithms such as anti-vibration and phase recovery. The feasibility of this method has been verified from both simulation and experimental levels, and good results have been achieved.

[0054] It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A vibration-proof method for a single-frame quantitative phase imaging interferometer, characterized in that: The steps include: S1. First, a spherical phase is introduced into the object light path in the interference light path, and the magnitude of the spherical phase is 4π~8π; S2. A single-frame image is collected by a polarization camera, and four polarization phase shift images are extracted. The phase shift caused by vibration is a global shift. The light intensity corresponding to the four polarization phase shift images is expressed as follows: In formula (1), I0(x, y, z) and ΔI(x, y, z) represent the background light and the detection light respectively; Indicates the phase to be measured; in, represents the sample phase, represents the spherical phase, Indicates the vibration phase; By performing addition and subtraction operations on formula (1), we can obtain: Then perform the inverse tangent operation to obtain the phase value to be measured S3, the obtained phase Perform unwrapping processing, that is, use the fast cosine least squares unwrapping algorithm to unwrap the phase; S4. Subtract the spherical phase from the unfolded phase to obtain the phase of the sample.

2. The anti-vibration method of the single-frame quantitative phase imaging interferometer according to claim 1 is characterized by introducing After spherical phase, the unwrapping algorithm fixes the phase minimum value to offset the vibration phase, thereby fixing the phase range to suppress vibration.

3. The anti-vibration method of the single-frame quantitative phase imaging interferometer according to claim 1, characterized in that: The introduced spherical phase has a magnitude of 6π.

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