A laser cavity diagnosis device and method based on double frame delay synchronization phase shift

Abstract

The application discloses a laser cavity diagnosis device and method based on double-frame delay synchronization phase shift, which comprises an excitation module and a detection module; the excitation module comprises a first laser, a first 1 / 2 wave plate, a polarization beam splitter prism, a beam splitter, an energy meter, a convex lens and a water tank; the detection module comprises a second laser, a beam expander lens group, a second 1 / 2 wave plate, a second polarization beam splitter prism, a third 1 / 2 wave plate, a first reflector, a second reflector, a fourth 1 / 2 wave plate, a third polarization beam splitter prism, a third reflector, a fourth polarization beam splitter prism, a first 1 / 4 wave plate, a first imaging lens, a first micro-polarization camera, a second 1 / 4 wave plate, a second imaging lens and a second micro-polarization camera. The application introduces a double-frame delay method in the traditional synchronous phase shift interference, overcomes the defects of the existing cavity detection technology, and realizes the observation of the instantaneous phase change in a single cavity pulsation period.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of laser-induced cavitation measurement, and particularly relates to a laser cavitation diagnosis device and method based on double-frame time-delay synchronous phase shift. BACKGROUND

[0002] Cavitation dynamics and mechanism research is an important topic in the field of fluid mechanics, and has significant engineering application value in many fields such as ship propulsion system, hydraulic machinery, biomedical engineering, etc. The cavitation generated when the local pressure of the fluid is lower than the saturated vapor pressure can produce an impact pressure of hundreds of MPa and a high-speed microjet of hundreds of meters per second at the moment of collapse. This physical effect not only causes cavitation erosion damage to the mechanical surface, but also causes pressure pulsation in the flow field and reduces energy conversion efficiency.

[0003] Compared with the method of generating cavitation by relying on flow field disturbance in traditional cavitation research, laser-induced cavitation technology has become an ideal means for cavitation mechanism research due to its unique physical advantages. By adjusting the pulse energy, pulse width and focusing parameters of the laser, a cavitation structure with good spherical symmetry can be accurately generated in a transparent medium, and the initial radius can be accurately controlled in the micron to millimeter range. This non-contact cavitation generation method effectively avoids the flow field disturbance caused by the introduction of traditional cavitation nuclei, providing a controllable physical model for the study of the pure mechanical behavior of cavitation.

[0004] The instantaneous changes of cavitation during the early stage of expansion and the late stage of collapse are obvious. The existing synchronous phase shift interferometry is limited in that it cannot capture the instantaneous phase change within a single cavitation pulsation cycle. The high-speed photography method has sufficient resolution but cannot obtain phase information. Therefore, achieving nanosecond-level time-delay phase observation research during a single cavitation pulsation period has become a problem to be solved in laser cavitation diagnosis technology. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of existing cavitation detection technology and provide a laser cavitation diagnosis device and method based on double-frame time-delay synchronous phase shift. The synchronous phase shift interferometry device can be used to obtain cavitation information before and after a nanosecond-level time delay provided by a laser beam. The structure is compact, the components used are common components and do not require special manufacturing, and the device is easy to debug. The principle of the synchronous phase shift interferometry method is simple, and the phase distribution to be measured can be recovered by four frames of phase shift interferometry images obtained at the same time.

[0006] To achieve the above purpose, the following technical solution is adopted: a laser cavitation diagnosis device based on double-frame time-delay synchronous phase shift, comprising an excitation module and a detection module.

[0007] The excitation module includes a first laser, a first half-wave plate, a first polarizing beam splitter, a beam splitter, an energy meter, a convex lens, and a water tank. After the first laser emits a high-energy laser beam, it passes through an attenuator composed of the first half-wave plate and the polarizing beam splitter in sequence. The laser energy is measured in real time using the beam splitter and the energy meter, and the convex lens is used to focus the laser beam on the water to generate cavitation.

[0008] The detection module includes a second laser, a beam expander group, a second half-wave plate, a second polarizing beam splitter, a third half-wave plate, a first reflecting mirror, a second reflecting mirror, a fourth half-wave plate, a third polarizing beam splitter, a third reflecting mirror, a fourth reflecting mirror, a fourth polarizing beam splitter, a first quarter-wave plate, a first imaging lens, a first micro-polarization camera, a second quarter-wave plate, a second imaging lens, and a second micro-polarization camera. The second laser emits a parallel beam through the beam expander group, which is split into two orthogonal linearly polarized beams by the second polarizing beam splitter. One beam serves as the first detection beam and passes through the third half-wave plate, while the other beam is delayed by the reflecting mirror and serves as the second detection beam and passes through the fourth half-wave plate. Both beams then pass through a synchronous phase-shifting system, so that both micro-polarization cameras acquire four laser cavitation interferograms with a phase difference of π / 2, and the two sets of interferograms have a certain time delay.

[0009] Furthermore, the fast axis direction of the third and fourth half-wave plates makes an angle of 22.5° with the polarization direction of their respective incident light.

[0010] Furthermore, the fast axis direction of the first and second quarter wave plates makes an angle of 45° with the fast or slow axis of the incident ray-polarized light.

[0011] Furthermore, the third polarizing beam splitter, the third reflecting mirror, the fourth reflecting mirror, the fourth polarizing beam splitter, the second quarter wave plate, the first imaging lens, the first micro-polarizing camera, the second quarter wave plate, the second imaging lens, and the second micro-polarizing camera constitute a synchronous phase-shifting system; the formulas for the light intensity after interference of the reference light and the test light reaching the two micro-polarizing cameras are both:

[0012]

[0013] Where I(x,y) is the intensity of the light after interference, I 测试 (x,y) represents the light intensity measured through the cavitation region, I 参考 (x,y) represents the light intensity of the reference light that did not pass through the cavitation region. Let φ(x,y) be the phase to be measured, and let φ(x,y) be the phase shift.

[0014] The formulas for the light intensity of polarization units in the four polarization directions are:

[0015]

[0016] Where I1(x,y), I2(x,y), I3(x,y), and I4(x,y) represent the light intensities on four polarization units whose transmission directions differ by 45°, respectively; thus, the phase of the cavitation bubble to be measured is obtained. for

[0017]

[0018] Furthermore, the micro-polarization camera includes four polarization units with polarization directions of 0°, 45°, 90°, and 135°.

[0019] A laser cavitation diagnostic method based on dual-frame delay synchronous phase shifting, implemented using the aforementioned diagnostic device, comprises the following steps:

[0020] Step 1: The laser beam emitted by the first laser is focused by a laser-resistant convex lens to form a high laser energy density spot, which excites and induces cavitation in water. During the cavitation pulsation, high-pressure shock waves and jets are generated.

[0021] Step 2: The laser beam emitted by the second laser is split into orthogonal linearly polarized light by the beam expander group, the second half-wave plate, and the second polarizing beam splitter. One beam is the first probe light, and the other beam is delayed by two mirrors to serve as the second probe light.

[0022] Step 3: The first probe light is split into p-light and s-light by the third half-wave plate and the third polarization beam splitter, which are located at an angle of 22.5° between the fast axis direction and the polarization direction of the incident light. The p-light is the test light that passes through the cavitation region, and the s-light is the reference light. After being combined by the fourth polarization beam splitter, the beam is imaged by the first imaging lens of the first micro-polarization camera.

[0023] Step 4: The second probe light is split into p-light and s-light by the fourth 1 / 2 wave plate and the third polarization beam splitter, which have an angle of 22.5° between the fast axis direction and the polarization direction of the incident light. The s-light is the test light that passes through the cavitation region, and the p-light is the reference light. After being combined by the fourth polarization beam splitter, the beam is imaged by the second imaging lens on the second micro-polarization camera.

[0024] Step 5: Four synchronous phase-shifted interference images with a phase shift of π / 2 were obtained on both micro-polarization cameras. The two sets of interference patterns have a delay on the order of nanoseconds.

[0025] Step 6: Process the four phase-shifting interferometric images using a four-step phase-shifting algorithm and a phase unwrapping algorithm to calculate the phase distribution to be measured.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The synchronous phase-shifting interference device can be used to provide cavitation information before and after a nanosecond delay by a laser beam. It has a compact structure, uses common components that do not require special manufacturing, and is easy to debug. The synchronous phase-shifting interference method has a simple principle. The phase distribution to be measured can be restored by analyzing four phase-shifting interference images obtained at the same time.

[0028] (2) The present invention introduces a two-frame delay method into the traditional synchronous phase-shifting interferometry, which overcomes the shortcomings of the existing cavitation detection technology and realizes the observation of instantaneous phase changes within a single cavitation pulsation period. Attached Figure Description

[0029] Figure 1 This is an optical path diagram of a laser diagnostic cavitation device and method based on dual-frame delay synchronous phase shifting disclosed in an embodiment of the present invention.

[0030] Figure 2 This is a laser cavitation interferogram acquired by a laser cavitation diagnostic device based on dual-frame delay synchronous phase shifting.

[0031] Figure 3 The laser cavitation phase is obtained based on the laser cavitation diagnosis method with dual-frame delay synchronous phase shift.

[0032] Reference numerals: 1-First laser, 2-First half-wave plate, 3-First polarizing beam splitter, 4-Beam splitter, 5-Energy meter, 6-Convex lens, 7-Water tank, 8-Second laser, 9-Beam expander group, 10-Second half-wave plate, 11-Second polarizing beam splitter, 12-Third half-wave plate, 13-First reflecting mirror, 14-Second reflecting mirror, 15-Fourth half-wave plate, 16-Third polarizing beam splitter, 17-Third reflecting mirror, 18-Fourth reflecting mirror, 19-Fourth polarizing beam splitter, 20-First quarter-wave plate, 21-First imaging lens, 22-First micro-polarizing camera, 23-Second quarter-wave plate, 24-Second imaging lens, 22-Second micro-polarizing camera. Detailed Implementation

[0033] This invention proposes a laser cavitation diagnostic device and method based on dual-frame delay synchronous phase shifting. The device includes an excitation module and a detection module, and the experimental optical path system is as follows: Figure 1 As shown.

[0034] The excitation module includes: a first laser 1, a first half-wave plate 2, a first polarizing beam splitter 3, a beam splitter 4, an energy meter 5, a convex lens 6, and a water tank 7. The detection module includes: a second laser 8, a beam expander group 9, a second half-wave plate 10, a second polarizing beam splitter 11, a third half-wave plate 12, a first reflecting mirror 13, a second reflecting mirror 14, a fourth half-wave plate 15, a third polarizing beam splitter 16, a third reflecting mirror 17, a fourth reflecting mirror 18, a fourth polarizing beam splitter 19, a first quarter-wave plate 20, a first imaging lens 21, a first micro-polarization camera 22, a second quarter-wave plate 23, a second imaging lens 24, and a second micro-polarization camera 25. Through the attenuator and energy meter composed of the half-wave plate and polarizing beam splitter in the excitation module, the energy level of the laser generating the cavitation bubble can be monitored in real time. The first probe beam is split into two linearly polarized beams with orthogonal polarization states by a second polarization beam splitter in the detection module. The first probe beam passes sequentially through a second half-wave plate, a third polarization beam splitter, a fourth polarization beam splitter, a first quarter-wave plate, and a first imaging lens before being imaged by a first micro-polarization camera. The second probe beam, after time delay by two mirrors, passes sequentially through a third half-wave plate, a third polarization beam splitter, a fourth polarization beam splitter, a second quarter-wave plate, and a second imaging lens before being imaged by a second micro-polarization camera. The two micro-polarization array cameras acquire laser cavitation interferometry images with phase differences of 0, π / 2, π, and 3π / 2, achieving high-resolution observation of nanosecond-level transient phase evolution.

[0035] The fast axis of the third and fourth half-wave plates forms an angle of 22.5° with the polarization direction of their respective incident light; the fast axis of the first and second quarter-wave plates forms an angle of 45° with the fast (or slow) axis of the incident linearly polarized light; the micro-polarization camera contains polarization units with four polarization directions (0°, 45°, 90° and 135°).

[0036] The principle of this device is as follows: The laser beam emitted by the first laser is focused by a laser-resistant convex lens to form a high-energy-density spot, which induces cavitation in water. An attenuator consisting of a first half-wave plate and a polarizing beam splitter, along with a beam splitter and an energy meter, are used to measure the laser energy in real time. The laser beam emitted by the second laser is expanded into a parallel beam by a beam expander group, and then passes through a second half-wave plate and a second polarizing beam splitter, where part is transmitted and part is reflected, forming a first and second probe beam with orthogonal polarization. The first probe beam is split into two orthogonal p-beams and s-beams by a third half-wave plate and a third polarizing beam splitter. The p-beam is the test beam passing through the cavitation region, and the s-beam is the reference beam. The two beams are simultaneously combined by a fourth polarizing beam splitter, then pass through a first quarter-wave plate to form left- and right-hand circularly polarized light. Finally, after passing through a first imaging lens, four interference images with phase shifts differing by π / 2 are generated on a first micro-polarization camera. Using the first and second mirrors to generate a delayed second probe light, the same method is used to finally produce four interference images on the second micro-polarization camera, with phase shifts differing by π / 2 in sequence.

[0037] Figure 2 The images show synchronous phase-shifting interferograms of laser cavitation bubbles, grouped into sets of four. The left image was acquired by the first micro-polarization camera, and the right image by the second micro-polarization camera. The expansion times of the laser cavitation bubbles are 600 ns and 603 ns, respectively. The polarization directions of the four interferograms in each group are 0°, 45°, 90°, and 135°, respectively.

[0038] Figure 3 The diagram shows three sets of laser cavitation phase distributions obtained through calculation, with expansion times of 600 ns and 603 ns, respectively.

[0039] This invention also provides a laser cavitation diagnosis method based on dual-frame delay synchronous phase shifting, the specific steps of which are as follows:

[0040] Step 1: First, turn on the first laser, adjust the attenuator composed of the first 1 / 2 wave plate and the polarizing beam splitter, and monitor the energy in real time with the beam splitter. The laser is focused by the convex lens to generate a cavitation bubble.

[0041] Step 2: Adjust the second half-wave plate so that the laser emitted from the second laser is converted into two linearly polarized beams with the same intensity and orthogonal polarization state after passing through the second polarization beam splitter.

[0042] Step 3: Adjust the third half-wave plate so that the first probe light is split into p1 light and s1 light of the same intensity by the third polarizing wind prism. The p1 light is used as the test light and passes through the cavitation region, and then is combined by the fourth polarizing beam splitter. Adjust the distance between the first and second reflectors to change the time delay of the second probe light. Adjust the fourth half-wave plate so that the second probe light is split into p2 light and s2 light of the same intensity by the third polarizing wind prism, and then is combined by the fourth polarizing beam splitter.

[0043] Step 4: The two combined laser beams pass through a quarter-wave plate to form left-handed and right-handed circularly polarized light. Finally, after passing through an imaging lens, four interference images with sequentially different phase shifts (π / 2) are generated on each of the two micro-polarization cameras, as shown below. Figure 2 As shown.

[0044] In this example, the time delay is determined by the sum of the distances L from the first reflecting mirror to the second polarizing beam splitter and the second reflecting mirror to the third polarizing beam splitter, and its time delay formula is:

[0045]

[0046] Where c is the speed of light, and assume that the Jones matrices of the two linearly polarized probe beams after passing through the second polarization peak beam splitter are E0=(1,0). T And E0 = (0,1) T The Jones matrix of a quarter-wave plate at 45° to the transmission axis is:

[0047]

[0048] The micro-polarization array comprises a series of polarizers, with the Jones matrix of the polarizers at an angle of θ to the transmission axis as follows:

[0049]

[0050] The reference and test beams are calculated using Jones matrices for four polarization directions. The resulting interference between the test and reference beams creates phase differences of 3π / 2, 0, π / 2, and π. Therefore, the phase to be measured is:

[0051]

[0052] Finally, the true phase can be recovered through phase unwrapping. The above derivation confirms that the laser cavitation diagnosis method based on dual-frame delay synchronous phase shift can obtain nanosecond-level phase changes during a single cavitation pulsation.

Claims

1. A laser cavity diagnosis device based on double frame delay synchronization phase shift, which realizes the observation of instantaneous phase change in a single cavity pulsation cycle, characterized in that, The excitation module and the detection module are included; The excitation module includes a first laser (1), a first... Waveplate (2), first polarizing beam splitter (3), beam splitter (4), energy meter (5), convex lens (6), and water tank (7); after the first laser (1) emits a high-energy laser beam, it passes through the first... After the attenuator composed of wave plate (2) and polarizing beam splitter (3), the laser energy is measured in real time by beam splitter (4) and energy meter (5), and cavitation is generated by focusing on water using convex lens (6); The detection module comprises a second laser (8), a beam expander (9), a second wave plate (10), a second polarization beam splitter prism (11), a third wave plate (12), a first mirror (13), a second mirror (14), a fourth wave plate (15), a third polarization beam splitter prism (16), a third mirror (17), a fourth mirror (18), a fourth polarization beam splitter prism (19), a first wave plate (20), a first imaging lens (21), a first micro-polarization camera (22), a second wave plate (23), a second imaging lens (24) and a second micro-polarization camera (25); the third polarization beam splitter prism (16), the third mirror (17), the fourth mirror (18), the fourth polarization beam splitter prism (19), the second wave plate (20), the first imaging lens (21), the first micro-polarization camera (22), the second wave plate (23), the second imaging lens (24) and the second micro-polarization camera (25) constitute a synchronous phase-shifting system; the second laser (8) emits parallel light beams through the beam expander (9), and the parallel light beams are divided into two beams of orthogonal linearly polarized light through the second wave plate (10) and the second polarization beam splitter prism (11), one of the two beams of orthogonal linearly polarized light is used as first detection light and passes through the third wave plate (12), and the other beam passes through the first mirror (13) and the second mirror (14) to delay the light path and is used as second detection light and passes through the fourth wave plate (15), and then both of the two beams of light pass through the synchronous phase-shifting system, so that both of the two micro-polarization cameras collect four laser cavitation interference patterns with a phase difference of π / 2, and the two groups of interference patterns have a nanosecond delay; the third wave plate (12) and the fourth wave plate (15) are arranged at an angle of 22.5° between the fast-axis direction and the polarization direction of the incident light; the first detection light passes through the third wave plate and the third polarization beam splitter prism at an angle of 22.5° between the fast-axis direction and the polarization direction of the incident light, and is divided into p light and s light, wherein the p light is test light passing through the cavitation region, and the s light is reference light; after being combined by the fourth polarization beam splitter prism, the first detection light passes through the first imaging lens and is imaged on the first micro-polarization camera; the second detection light passes through the fourth wave plate and the third polarization beam splitter prism at an angle of 22.5° between the fast-axis direction and the polarization direction of the incident light, and is divided into p light and s light, wherein the s light is test light passing through the cavitation region, and the p light is reference light; after being combined by the fourth polarization beam splitter prism, the second detection light passes through the second imaging lens and is imaged on the second micro-polarization camera.

2. The dual frame time delay synchronization phase-shift based laser cavitation diagnostic device according to claim 1, characterized in that: The first The fast axis direction of the wave plate (20) and the second The angle between the fast axis direction of the wave plate (23) and the fast axis or the slow axis of the incident linearly polarized light is 45°.

3. The dual frame time delay synchronization phase-shift based laser cavitation diagnostic device according to claim 1, characterized in that: The light intensity formula of the reference light and the test light after interference is as follows: ； wherein, is the light intensity after interference, is the light intensity of the test light passing through the cavity region, is the light intensity of the reference light not passing through the cavity region, is the phase to be measured, is the phase shift amount; The light intensity formula of the polarization units with four polarization directions is as follows: ； wherein, , , and are the light intensities on the four polarization units which are in turn 45° apart in the vibration direction; thus, the phase of the cavitation to be measured is 。 4. The dual frame time delay synchronization phase-shifting based laser cavitation diagnostic apparatus according to claim 1, characterized in that: The micro-polarization camera includes polarization units with four polarization directions of 0°, 45°, 90° and 135°.

5. A laser cavitation diagnosis method based on double-frame time delay synchronization phase shift, characterized in that, The device is implemented according to any one of claims 1-4, and the steps are as follows: Step 1: the laser beam emitted by the first laser passes through the laser-resistant convex lens to form a high laser energy density spot, and the water is excited to induce cavitation bubbles, and the cavitation bubbles generate a high-pressure shock wave and a jet flow during pulsation; Step 2, the laser beam emitted by the second laser passes through a beam expander, a second wave plate, and a second polarization beam splitter prism to divide into two linearly polarized lights that are orthogonal to each other, one of which is the first probe light, and the other of which is delayed by two mirrors to serve as the second probe light; Step 3, the third wave plate with the angle of 22.5° between the fast axis direction of the first probe light and the polarization direction of the incident light divides the first probe light into p light and s light, wherein the p light is the test light passing through the bubble region, and the s light is the reference light; after being combined by the fourth polarization beam splitting prism, the first probe light is imaged on the first micro-polarization camera through the first imaging lens. Step 4, the second probe light passes through a fourth wave plate with an angle of 22.5° between the fast axis direction and the polarization direction of the incident light and a third polarization beam splitting prism to divide into p light and s light, wherein the s light is the test light passing through the bubble region, and the p light is the reference light; after being combined by a fourth polarization beam splitting prism, the second imaging lens is used for imaging on a second micro-polarization camera; Step 5, four phase-shifted synchronous phase-shifted interferograms are obtained on both micro-polarization cameras, with nanosecond delay between the two sets of interferograms. Step 5, four phase-shifted synchronous phase-shifted interferograms are obtained on both micro-polarization cameras, with nanosecond delay between the two sets of interferograms. Step 6: four-step phase shifting algorithm and phase unwrapping algorithm are used to process the four phase shifting interference images, and the phase distribution to be measured is calculated.

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