Device and method for automatically judging laser damage based on synchronous phase shift

Abstract

The invention discloses a device and a method for automatically judging laser damage based on synchronous phase shift. The method comprises the following steps: adjusting light beams output by a laser into linear polarization parallel light beams; the linear polarization parallel light beam is equally divided into two light beams, one light beam serves as reference light, and the other light beam serves as test light and enters an optical element to be tested; adjusting the polarization direction of the reference light to change by 90 degrees, and adjusting the polarization direction of the test light to change by 90 degrees; interference is carried out on the reference light and the test light after polarization direction adjustment, and the reference light and the test light are adjusted into linearly polarized light containing measured wave difference information; performing synchronous phase-shifting image acquisition on the linearly polarized light to obtain a synchronous phase-shifting interferogram; based on the synchronous phase-shifting interferogram, a real phase of the to-be-measured optical element is obtained through restoration by using a phase-shifting algorithm; calculating the real phase of the to-be-measured optical element to obtain the surface type of the to-be-measured optical element; and performing automatic damage judgment on the surface type of the to-be-detected optical element through the upper computer and outputting a judgment result. According to the invention, the non-contact high-spatial-resolution automatic judgment of the laser damage on the surface of the optical element can be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical precision detection, and in particular to a device and method for automatically judging laser damage based on synchronous phase shifting. Background Art

[0002] Laser damage threshold (LIDT) is one of the key indicators for measuring the performance of high-grade optical devices. It is of irreplaceable importance to ensure that the optical system can maintain stable and efficient operation when subjected to high-intensity laser irradiation. During the manufacturing and subsequent transportation of optical devices, due to the limitations of process precision and the potential influence of environmental factors, initial defects such as scratches, contamination, and tiny cracks are easily formed on the surface of optical components. These seemingly insignificant flaws often become trigger points for inducing damage when encountering high-intensity laser irradiation, which in turn causes local or overall performance degradation of optical components. In severe cases, it may even lead to a significant decrease in beam quality and serious damage to the overall stability of the system.

[0003] Traditionally, the methods used are phase contrast microscopy and plasma flash. Phase contrast microscopy is a standard detection method proposed by the international standard ISO 11254. Its detection results are relatively accurate, but the detection of laser damage mainly relies on manual visual inspection. This method is not only inefficient and time-consuming, but also often difficult to ensure the accuracy and consistency of the detection results when faced with complex and changeable damage forms. In addition, manual detection is also limited by the experience and subjective judgment of the inspectors, further increasing the risk of misjudgment and missed detection.

[0004] With the continuous development of laser technology and optical detection technology, some scholars have proposed laser damage detection based on white light interferometry. This method can detect surface damage of optical components through optical interference technology combined with image processing algorithms, but the seismic resistance of precision devices such as gratings in this method is poor, and it is difficult to implement in actual application.

[0005] In the field of vibration-resistant measurement technology in recent years, polarization cameras have been widely introduced into interferometric measurement systems to achieve instant phase measurement based on spatial phase shifting technology. This method abandons the traditional time phase shift method that relies on mechanical or electrical devices and instead uses polarization cameras to perform spatial synchronous phase modulation. This strategy aims to effectively alleviate the impact of external environmental factors such as vibration, air disturbance and temperature drift on the accuracy of interferometric measurement. This meets the high standard requirements for vibration-resistant performance in in-situ measurement of optical components.

[0006] Later, some scholars used a combination of a quarter-wave plate and a beam splitter to cleverly integrate four frames of different phase-shifted interference patterns into a single CCD camera for synchronous acquisition after spatial distribution, thus achieving cost savings. However, this solution has the disadvantages of complex structure and cumbersome debugging process.

[0007] Therefore, it is necessary to study an automatic laser damage judgment device and method based on synchronous phase shifting to overcome the above defects. Summary of the invention

[0008] The purpose of the present invention is to address the problems existing in the above-mentioned prior art and to provide a device and method for automatic laser damage judgment based on synchronous phase shifting, which can solve the difficult problem of balancing efficient automatic judgment and accurate damage identification in laser damage detection, and can significantly improve the automation and flexibility of the detection process while ensuring the accuracy of damage detection.

[0009] The technical solution to achieve the purpose of the present invention is: on the one hand, a method for automatic determination of laser damage based on synchronous phase shift is provided, the method comprising:

[0010] Step 1, adjusting the light beam output by the laser to a linearly polarized parallel light beam;

[0011] Step 2, dividing the linearly polarized parallel light beam into two beams, one beam of light being used as reference light and the other beam of light being used as test light and incident on the optical element to be tested;

[0012] Step 3, adjusting the polarization direction of the reference light to change it by 90°, and adjusting the polarization direction of the test light to change it by 90°;

[0013] Step 4, interfering the reference light with the polarization direction adjusted with the test light, and adjusting them into linear polarized light containing the measured wave difference information;

[0014] Step 5, performing synchronous phase-shifting image acquisition on the linear polarization to obtain a synchronous phase-shifting interference pattern;

[0015] Step 6, based on the synchronous phase-shifting interferogram, the real phase of the optical element to be measured is restored by using a phase-shifting algorithm;

[0016] Step 7, calculating the real phase of the optical element to be measured to obtain the surface shape of the optical element to be measured;

[0017] Step 8: The host computer automatically determines the damage of the surface of the optical element to be measured and outputs the determination result.

[0018] Furthermore, in step 5, four synchronous phase-shifted images are collected, and in step 6, the real phase of the optical element to be measured is restored using a four-step phase-shifting algorithm. The specific formula is:

[0019]

[0020] In the formula, is the real phase of the optical element to be measured, I α is the background intensity of the interference light, I β is the amplitude of the interference light, I1 ,I 2 ,I 3 and I 4 They are phase shifts that differ by 90° respectively.

[0021] Furthermore, the step 7 of automatically judging the damage of the surface of the optical element to be measured and outputting the judgment result by the host computer specifically includes:

[0022] Perform 1-on-1 calibration on the damage threshold of the optical element to be tested through the host computer;

[0023] Set the maximum surface phase M and error value N under the damage threshold;

[0024] Determine whether the following conditions are met: the phase of the optical element to be tested under the action of laser is not within the range of [0, M±N], and the surface phase of the optical element to be tested does not gradually recover to the original phase according to its recovery trend after the laser irradiation ends; if the conditions are met, it is determined that the surface of the optical element to be tested is damaged, otherwise it is determined that there is no damage.

[0025] Furthermore, the method further includes, after step 5 and before step 6, executing:

[0026] The synchronous phase-shifting interference pattern is subjected to filtering and noise reduction processing.

[0027] On the other hand, a laser damage automatic judgment device based on synchronous phase shift is provided, the device comprising a laser, a beam expander, a collimator, a half-wave plate, a polarization beam splitter, a first quarter-wave plate, a beam combiner, a fixture, a second quarter-wave plate, a compensation plate, a first reflector, a third quarter-wave plate, a second reflector, an interference filter, a micro-polarization column camera, a two-dimensional mobile platform and a host computer;

[0028] The fixture is used to clamp the optical element to be measured and is installed on the two-dimensional moving platform;

[0029] The light beam emitted by the laser forms a linearly polarized parallel light beam after passing through the beam expander, collimator and half-wave plate. The linearly polarized parallel light beam is evenly divided into two light beams after passing through the polarization beam splitter prism, one of which is incident on the first reflector after passing through the second quarter-wave plate and the compensation plate in sequence, and then returns to the original path after being reflected by the first reflector to form a reference light, and the other light is incident on the optical element to be measured after passing through the first quarter-wave plate and the beam combiner in sequence, and then returns to the original path after being reflected by the element to be measured to form a test light; the reference light and the test light are respectively reflected and transmitted by the polarization beam splitter prism and then combined into one light beam, which is reflected by the second reflector and passes through the interference filter, and then the micro-polarization array camera collects four synchronous phase-shifted images and transmits them to the host computer, and the host computer automatically judges the damage of the surface of the optical element to be measured and outputs the judgment result.

[0030] Furthermore, the fast axis direction of the first quarter wave plate is 45° to the P polarization direction, the fast axis direction of the second quarter wave plate is 45° to the P polarization direction, and the fast axis direction of the third quarter wave plate is 45° to the polarization directions of the reference light and the test light.

[0031] Compared with the prior art, the present invention has the following significant advantages:

[0032] (1) Based on the synchronous phase shifting technology and the interference principle, the present invention can collect multiple interference patterns with fixed phase differences at the same time by precisely controlling the phase difference of the light wave, thereby effectively avoiding the influence of external factors such as environmental vibration on the measurement results. The application of this technology greatly improves the accuracy and stability of laser damage judgment.

[0033] (2) The present invention realizes the automation and intelligence of laser damage judgment. The online damage detection system in the device can automatically capture and analyze the image changes on the sample surface before and after laser irradiation. By comparing the image differences before and after damage, it can accurately determine whether the sample is damaged by the laser. At the same time, combined with advanced data processing algorithms, the present invention can also quantitatively evaluate the degree of damage, providing more accurate and reliable laser damage threshold data for scientific research and industrial applications. This automated and intelligent judgment method not only improves work efficiency, but also reduces human errors.

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 FIG. 1 is a structural diagram of a laser damage automatic judgment device based on synchronous phase shifting in one embodiment of the present invention.

[0036] Figure 2 The flowchart of the automatic laser damage judgment method based on synchronous phase shifting in one embodiment of the present invention.

[0037] Figure 3 Four synchronous phase-shifting interference patterns obtained in one embodiment.

[0038] Figure 4 This is a true phase distribution diagram without laser damage measured in an embodiment.

[0039] Figure 5 FIG. 1 is a real phase distribution diagram of laser damage measured in one embodiment. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0041] It should be noted that if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0042] In one embodiment, in combination Figure 2 , provides a method for automatic determination of laser damage based on synchronous phase shift, the method comprising the following steps:

[0043] Step 1, adjusting the light beam output by the laser to a linearly polarized parallel light beam;

[0044] Step 2, dividing the linearly polarized parallel light beam into two beams, one beam of light being used as reference light and the other beam of light being used as test light and incident on the optical element to be tested;

[0045] Step 3, adjusting the polarization direction of the reference light to change it by 90°, and adjusting the polarization direction of the test light to change it by 90°;

[0046] Step 4, interfering the reference light with the polarization direction adjusted with the test light, and adjusting them into linear polarized light containing the measured wave difference information;

[0047] Step 5, performing synchronous phase shift image acquisition on the linear polarization to obtain a synchronous phase shift interference pattern, such as Figure 3 As shown;

[0048] Step 6, based on the synchronous phase-shifting interferogram, the real phase of the optical element to be measured is restored by using a phase-shifting algorithm; Figure 4 , Figure 5 Shown is the real phase distribution diagram with or without laser damage measured in the example;

[0049] Step 7, calculating the real phase of the optical element to be measured to obtain the surface shape of the optical element to be measured;

[0050] Step 8: The host computer automatically determines the damage of the surface of the optical element to be measured and outputs the determination result.

[0051] Preferably, in some embodiments, four synchronous phase-shifted images are collected in step 5, and in step 6, the real phase of the optical element to be measured is restored using a four-step phase-shifting algorithm. The specific formula is:

[0052]

[0053] In the formula, is the real phase of the optical element to be measured, I α is the background intensity of the interference light, I β is the amplitude of the interference light, I 1 ,I 2 ,I 3 and I 4 They are phase shifts that differ by 90° respectively.

[0054] Further, in one embodiment, the step 7 of automatically judging the damage of the surface of the optical element to be measured by the host computer and outputting the judgment result specifically includes:

[0055] Perform 1-on-1 calibration on the damage threshold of the optical element to be tested through the host computer;

[0056] Set the maximum surface phase M and error value N under the damage threshold;

[0057] Determine whether the following conditions are met: the phase of the optical element to be tested under the action of laser is not within the range of [0, M±N], and the surface phase of the optical element to be tested does not gradually recover to the original phase according to its recovery trend after the laser irradiation ends; if the conditions are met, it is determined that the surface of the optical element to be tested is damaged, otherwise it is determined that there is no damage.

[0058] Furthermore, in one embodiment, the method further includes, after step 5 and before step 6, executing:

[0059] The synchronous phase-shifting interference pattern is subjected to filtering and noise reduction processing.

[0060] Preferably, in some embodiments, the filtering and noise reduction process uses a sine-cosine filtering algorithm, which specifically includes performing sine and cosine processing on the phase value Δ(x, y) to obtain two continuous components s(x, y) and c(x, y):

[0061]

[0062] At this time, the phase image is divided into two components, and then the mean filter is used for calculation. Taking any pixel point (i, j) in the mean filter as the center point, the size of the window is m×n, and the sinusoidal phase image after filtering is The cosine phase value after filtering is

[0063]

[0064] w represents all the pixels in m×n. The sine and cosine components are processed by inverse tangent to obtain the complete phase after denoising.

[0065]

[0066] In one embodiment, in combination Figure 1 , provides a laser damage automatic judgment device based on synchronous phase shift, the device includes a laser 1, a beam expander 2, a collimator 3, a half-wave plate 4, a polarization beam splitter 5, a first quarter-wave plate 6, a beam combiner 7, a fixture 8, a second quarter-wave plate 9, a compensation plate 10, a first reflector 11, a third quarter-wave plate 12, a second reflector 13, an interference filter 14, a micro-polarization column camera 15, a two-dimensional mobile platform 16 and a host computer 17;

[0067] The fixture 8 is used to clamp the optical element to be measured and is installed on the two-dimensional moving platform 16;

[0068] The light beam emitted by the laser 1 forms a linearly polarized parallel light beam after passing through the beam expander 2, the collimator 3, and the half-wave plate 4. The linearly polarized parallel light beam is evenly divided into two light beams after passing through the polarization beam splitter prism 5, one of which is incident on the first reflector 11 after passing through the second quarter-wave plate 9 and the compensation plate 10 in sequence, and then returns to the original path after being reflected by the first reflector 11 to form a reference light, and the other light is incident on the optical element to be measured after passing through the first quarter-wave plate 6 and the beam combiner 7 in sequence, and then returns to the original path after being reflected by the element to be measured to form a test light; the reference light and the test light are respectively reflected and transmitted by the polarization beam splitter prism 5 and then combined into a light beam, which is reflected by the second reflector 13 and passes through the interference filter 14, and then the micro-polarization array camera 15 performs four synchronous phase-shifted image acquisition and transmits them to the host computer 17, and the host computer 17 automatically judges the damage of the surface of the optical element to be measured and outputs the judgment result.

[0069] Preferably, in some embodiments, the laser 1 is a He-Ne laser with a wavelength of 632.8 nm.

[0070] Preferably, in some embodiments, the fast axis direction of the first quarter wave plate 6 is 45° to the P polarization direction, the fast axis direction of the second quarter wave plate 9 is 45° to the P polarization direction, and the fast axis direction of the third quarter wave plate 12 is 45° to the polarization directions of the reference light and the test light.

[0071] Preferably, in some embodiments, the spectral range of the polarization beam splitter prism 5 is 300nm-2500nm.

[0072] Preferably, in some embodiments, the spectral range of the beam combiner 7 is 600nm-2500nm.

[0073] The present invention can realize non-contact high spatial resolution automatic judgment of laser damage on the surface of an optical element.

[0074] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for automatic laser damage determination based on synchronous phase shifting, characterized in that: The method comprises: Step 1, adjusting the light beam output by the laser to a linearly polarized parallel light beam; Step 2, dividing the linearly polarized parallel light beam into two beams, one beam of light being used as reference light and the other beam of light being used as test light, and incident on the optical element to be tested; Step 3, adjusting the polarization direction of the reference light to change by 90°, and adjusting the polarization direction of the test light to change by 90°; Step 4, interfering the reference light with the polarization direction adjusted with the test light, and adjusting them into linear polarized light containing the measured wave difference information; Step 5, performing synchronous phase-shifting image acquisition on the linear polarization to obtain a synchronous phase-shifting interference pattern; Step 6, based on the synchronous phase-shifting interferogram, the real phase of the optical element to be measured is restored by using a phase-shifting algorithm; Step 7, calculating the real phase of the optical element to be measured to obtain the surface shape of the optical element to be measured; Step 8: The host computer automatically determines the damage of the surface of the optical element to be measured and outputs the determination result.

2. The method for automatic laser damage determination based on synchronous phase shifting according to claim 1 is characterized in that: In step 5, four synchronous phase-shifted images are collected, and in step 6, the real phase of the optical element to be measured is restored using a four-step phase-shifting algorithm. The specific formula is: In the formula, is the real phase of the optical element to be measured, I α is the background intensity of the interference light, I β is the amplitude of the interference light, and I1, I2, I3 and I4 are phase shifts that differ by 90° respectively.

3. The method for automatic laser damage determination based on synchronous phase shifting according to claim 1 is characterized in that: Step 7, in which the host computer automatically determines the damage of the surface of the optical element to be measured and outputs the determination result, specifically includes: Perform 1-on-1 calibration on the damage threshold of the optical element to be tested through the host computer; Set the maximum surface phase M and error value N under the damage threshold; Determine whether the following conditions are met: the phase of the optical element to be tested under the action of laser is not within the range of [0, M±N], and the surface phase of the optical element to be tested does not gradually recover to the original phase according to its recovery trend after the laser irradiation ends; if the conditions are met, it is determined that the surface of the optical element to be tested is damaged, otherwise it is determined that there is no damage.

4. The method for automatic laser damage determination based on synchronous phase shifting according to claim 1 is characterized in that: The method further comprises, after step 5 and before step 6, executing: The synchronous phase-shifting interference pattern is subjected to filtering and noise reduction processing.

5. The method for automatic laser damage determination based on synchronous phase shifting according to claim 4 is characterized in that: The filtering and noise reduction process adopts a sine-cosine filtering algorithm.

6. A laser damage automatic judgment device based on synchronous phase shifting for implementing the method described in any one of claims 1 to 5, characterized in that: The device comprises a laser (1), a beam expander (2), a collimator (3), a half-wave plate (4), a polarization beam splitter (5), a first quarter-wave plate (6), a beam combiner (7), a fixture (8), a second quarter-wave plate (9), a compensation plate (10), a first reflector (11), a third quarter-wave plate (12), a second reflector (13), an interference filter (14), a micro-polarization array camera (15), a two-dimensional mobile platform (16) and a host computer (17); The fixture (8) is used to clamp the optical element to be measured and is installed on the two-dimensional moving platform (16); The light beam emitted by the laser (1) passes through the beam expander (2), the collimator (3) and the half-wave plate (4) to form a linearly polarized parallel light beam. The linearly polarized parallel light beam passes through the polarization beam splitter (5) to be equally divided into two light beams. One of the light beams passes through the second quarter-wave plate (9) and the compensation plate (10) in sequence and then enters the first reflector (11). After being reflected by the first reflector (11), it returns along the original path to form a reference light. The other light beam passes through the first quarter-wave plate (6) and the beam combiner (7) in sequence. The reference light and the test light are then incident on the optical element to be tested, and then reflected by the element to be tested and returned along the original path to form test light; the reference light and the test light are respectively reflected and transmitted by the polarization beam splitter prism (5) and then combined into a beam of light, which is reflected by the second reflector (13) and passes through an interference filter (14), after which the micro-polarization array camera (15) collects four synchronous phase-shifted images and transmits them to a host computer (17), which automatically determines the damage to the surface of the optical element to be tested and outputs the determination result.

7. The automatic laser damage judgment device based on synchronous phase shifting according to claim 6 is characterized in that: The laser (1) is a He-Ne laser with a wavelength of 632.8 nm.

8. The laser damage automatic judgment device based on synchronous phase shift according to claim 6 is characterized in that: The fast axis direction of the first quarter wave plate (6) is 45° to the P polarization direction, the fast axis direction of the second quarter wave plate (9) is 45° to the P polarization direction, and the fast axis direction of the third quarter wave plate (12) is 45° to the polarization directions of the reference light and the test light.

9. The laser damage automatic judgment device based on synchronous phase shift according to claim 6 is characterized in that: The spectral range of the polarization beam splitter prism (5) is 300nm-2500nm.

10. The automatic laser damage judgment device based on synchronous phase shift according to claim 6, characterized in that: The spectral range of the beam combining mirror (7) is 600nm-2500nm.

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