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CN-122016858-A - Optical element surface damage detection device and detection method based on liquid crystal light valve

CN122016858ACN 122016858 ACN122016858 ACN 122016858ACN-122016858-A

Abstract

The device adopts the liquid crystal light valve to form a programmable dynamic Fresnel lens or a grating, so that an illumination beam can two-dimensionally scan the whole surface of a sample to be measured in a space range, and the device combines optical fiber transmission and high-sensitivity detection to realize mechanical motion-free measurement of the surface damage of the element. The device has the characteristics of small volume and light weight, realizes the online real-time direct detection of the surface damage of the element after the strong laser irradiation of different times, and provides accurate basis for the damage state of the element and the timely replacement of the element.

Inventors

  • NI KAIZAO
  • LI LINGQIAO
  • SUI ZHAN
  • CHEN JIAXING

Assignees

  • 中国科学院上海光学精密机械研究所

Dates

Publication Date
20260512
Application Date
20260413

Claims (9)

  1. 1. The optical element surface damage detection device based on the liquid crystal light valve is characterized by comprising an illumination light source (1), a first coupler (2), an optical fiber (3), a second coupler (4), a band-pass filter (5), the liquid crystal light valve (6), a sample (7), a third coupler (8), a focusing lens (9), a photoelectric detector (10) and a control processor (11); The light beam emitted by the illumination light source (1) enters the optical fiber (3) through the first coupler (2), is transmitted through the optical fiber (3), exits from the second coupler (4), and irradiates onto the liquid crystal light valve (6) through the band-pass filter (5); The light-sensitive surface of the photoelectric detector (10) is characterized in that the emergent surface of the liquid crystal light valve (6) faces the surface of a sample (7) to be detected, so that an illumination light beam modulated by the liquid crystal light valve (6) is directly irradiated to the surface of the sample (7) to be detected, or is irradiated to the surface of the sample (7) to be detected through an additional optical element, and scattered light generated by surface damage of the sample (7) to be detected is transmitted to the third coupler (8) through the optical fiber (3) after passing through the liquid crystal light valve (6), the band-pass filter (5) and the second coupler (4) in sequence and is converged to the light-sensitive surface of the photoelectric detector (10) through the focusing lens (9); the signal output end of the photoelectric detector (10) is electrically connected with the signal input end of the control processor (11), and the control signal output end of the control processor (11) is electrically connected with the control end of the liquid crystal light valve (6); the control processor (11) is used for programming and controlling the liquid crystal light valve (6) to generate a dynamically adjustable light beam modulation element, the light beam modulation element is a Fresnel lens or a grating, and is used for controlling the liquid crystal light valve (6) to refresh parameters of the light beam modulation element so as to realize two-dimensional scanning of a focusing light spot on the surface of the sample (7) to be detected, and synchronously collecting scattered light signals output by the photoelectric detector (10).
  2. 2. The device for detecting the surface damage of the optical element based on the liquid crystal light valve according to claim 1, wherein the illumination light source (1) is a narrow-band light source, and the light transmission band of the band-pass filter (5) is matched with the emission band of the illumination light source (1) so as to inhibit stray light.
  3. 3. The device for detecting surface damage of optical element based on liquid crystal light valve according to claim 1, wherein the liquid crystal light valve (6) is a reflective or transmissive spatial light modulator, and the control processor (11) loads a phase diagram or an amplitude diagram to the liquid crystal light valve (6) to generate a fresnel lens, and the fresnel lens is of an amplitude type or a phase type.
  4. 4. The device for detecting surface damage of optical element based on liquid crystal light valve according to claim 1, wherein the additional optical element comprises a lens (12), the lens (12) is arranged between the liquid crystal light valve (6) and the sample (7) to be detected, the control processor (11) is programmed to control the liquid crystal light valve (6) to generate a grating, an outgoing light beam modulated by the liquid crystal light valve (6) is focused on the surface of the sample (7) to be detected through the lens (12), and the position of a focusing light spot on the surface of the sample (7) to be detected is changed by changing the period parameter of the grating.
  5. 5. The device for detecting the surface damage of the optical element based on the liquid crystal light valve according to claim 1, wherein the control processor (11) is further configured to set a focal length and a central position coordinate of a fresnel lens generated by the liquid crystal light valve (6), or set a period parameter of a grating, so as to control a two-dimensional scanning movement of a focusing light spot on the surface of the sample (7), and a step length of the two-dimensional scanning is equal to a diameter of the focusing light spot on the surface of the sample (7).
  6. 6. A method for detecting surface damage by using the optical element surface damage detection device based on the liquid crystal light valve according to any one of claims 1-5, characterized in that the method adopts the control processor (11) to program and control the liquid crystal light valve (6) to dynamically generate fresnel lenses or gratings, and the parameters thereof are refreshed to make the illumination light spot do two-dimensional stepping scanning without mechanical movement on the surface of the sample (7) to be detected, so as to synchronously collect scattered light signals of all scanning points, reconstruct damage distribution diagram, and realize multiple comparison monitoring, and the specific steps are as follows: Step 1), an illumination light source (1) is turned on, a control processor (11) is programmed to modulate a liquid crystal light valve (6) to generate a Fresnel lens or a grating, corresponding parameters are set, and an illumination light beam is focused to the edge vertex position of the surface of a sample (7) to be detected; step 2) the control processor (11) is programmed to set the Fresnel lens center or grating period parameters to form a scanning movement coordinate position array: wherein, (x 1 ,y 1 ) is the scanning starting position of the edge vertex, and the movement distance of the focusing light spot along the x direction and the y direction is the light spot diameter d of the illumination light beam focused on the sample surface through the Fresnel lens or the grating and the lens respectively, namely x n -x n-1 =d,y m -y m-1 =d, n=1-N, and m= 1~M; Step 3) a control processor (11) sequentially gives a central coordinate of scanning movement to the liquid crystal light valve (6) according to the sequence of the first x-direction and the second y-direction, so that the central coordinate or the grating period parameter of the Fresnel lens generated by the liquid crystal light valve (6) is dynamically refreshed, and a focusing light spot moves in two dimensions on the surface of the sample (7) to be detected, and covers the whole surface to be detected point by point; Step 4), after changing the central coordinate of the Fresnel lens or the grating period parameter each time, the control processor (11) triggers the photoelectric detector (10) to synchronously collect scattered light signals generated by the current coordinate point, and the signal intensity is associated with the current coordinate and stored; Step 5) after full-caliber scanning and scattering signal acquisition are completed, the control processor (11) reconstructs an injury distribution image of the surface of the sample (7) to be detected according to two-dimensional distribution of the acquired scattering signals, an image processing algorithm is adopted to extract the injury point position and the area of the surface of the sample (7), and the severity of the injury of the surface of the sample is judged; And 6) repeating the steps 1) to 5) after the next high-energy laser action is carried out on the sample (7) to be detected, obtaining the damage point position and the area of the sample surface after the next high-energy laser action, comparing the damage point position and the area with the damage point position and the area of the previous high-energy laser action, and judging the damage growth condition of the sample surface and judging whether the damage degree reaches the scrapping degree or not.
  7. 7. The method of surface damage detection according to claim 6, wherein the focal spot position is moved in step 3) by changing the central coordinates of the fresnel lens when the liquid crystal light valve (6) produces the fresnel lens, and the focal spot position is moved in step 3) by changing the period parameters of the grating when the liquid crystal light valve (6) produces the grating and the device comprises the lens (12).
  8. 8. The method of claim 6, wherein the image processing algorithm in step 5) includes background subtraction, adaptive thresholding, morphological filtering and connected domain analysis to accurately extract the location, area and relative scattering intensity of the lesion point from the scattering signal distribution.
  9. 9. The method for detecting surface damage according to claim 6, wherein the specific way of determining the damage growth in step 6) is: performing space matching on the current extracted damage point and the previous damage point, and regarding the same damage point if the center distance between the two damage points is smaller than 1.5 times of the focused spot diameter d; Calculating the area growth coefficient of each matched damage point, namely the ratio of the current area to the previous area; If a new damage point appears or the area growth coefficient of the original damage point exceeds a preset threshold value, an early warning signal is sent out; If the proportion of the total damage area to the light transmission caliber of the sample (7) to be detected exceeds a preset value or the diameter of a single damage point exceeds a preset size, judging that the sample (7) to be detected reaches the scrapping degree.

Description

Optical element surface damage detection device and detection method based on liquid crystal light valve Technical Field The invention relates to the technical field of detection of surface damage of an optical element in a high-power strong laser system, in particular to a detection device and a detection method of surface damage of an optical element based on a liquid crystal light valve, which are suitable for online, in-situ and real-time surface damage detection of the optical element after high-energy laser irradiation in the strong laser system. Background The high-power strong laser system plays an important role in the fields of high-energy research, high-end instruments and national defense. A large number of optical elements used in the laser can generate surface damage under the action of high-energy laser, and the surface damage can block laser output, so that the output flux of the system is seriously reduced. The stray light generated can also affect the operation of other components in the system. At the same time, the surface damage will also change the beam distribution, affecting the beam quality. Under the action of different times of high-energy laser, the surface damage of the optical element in the system can be gradually increased, and the element can be disabled or even scrapped when the damage is serious, so that the system can not work directly. Therefore, on-line detection and monitoring of the surface damage of the optical element in the high-power strong laser system are needed, the surface condition is dynamically managed, and a basis is provided for timely element replacement. Surface damage to optical elements loaded in a strong laser system currently relies mainly on external visual inspection or energy sampling monitoring. The method comprises the steps of sampling and projecting laser output by a system on a screen through a sampling mirror, and subjectively judging the damage condition of elements in the system by observing whether a projection light spot has a dark spot and a local brightness mutation area or not and the size of a shielding area. In addition, the energy distribution conditions of different positions of the projected light spots are measured through the moving sampling of the energy measuring system, and the damage condition of the internal elements of the system is judged in sequence. The method is external indirect measurement, is influenced by light beam transmission, has limited measurement accuracy, cannot detect in real time after the single laser acts, and cannot accurately judge the damage growth condition. Currently, detection of surface damage of an optical element in a strong laser system mainly depends on two modes: Firstly, the external visual inspection method is to project the laser output by the system onto a screen through a sampling mirror, and an operator visually observes whether dark spots, local brightness mutation areas or shielding areas exist in the projected light spots, so that the damage condition of the internal elements of the system is subjectively judged. The method is greatly influenced by human factors, has poor accuracy and cannot realize quantitative measurement. And secondly, an energy sampling measurement method is used for measuring the energy distribution of different positions of the projected light spots point by moving an energy measurement probe, so as to indirectly infer the damage condition of the element surface. Although the method is improved compared with a visual method, the method still belongs to external indirect measurement, diffraction, scattering and the like in a laser transmission path are influenced, and the measurement accuracy is limited. Both the above methods cannot detect the element surface in real time, in situ and directly after the single-shot high-energy laser action, and also cannot accurately track the growth process of damage along with the laser incidence, so that the effective management of the system on the element health state is limited. Disclosure of Invention The invention aims to overcome the defects that the existing method for detecting the damage to the surface of an optical element in a strong laser system depends on external indirect measurement (projection visual observation or energy sampling), cannot realize online, in-situ, real-time and objective detection of the damage to the surface of the element, cannot acquire the damage state immediately after the action of single-shot high-energy laser, cannot accurately track the growth process of the damage along with the laser, and has large volume, complex structure and inconvenience for integration in the strong laser system. The invention provides an optical element surface damage detection device and method based on a liquid crystal light valve, which realize the on-line scanning detection with no mechanical movement, miniaturization, high precision and programmability. In order to achieve the above purpose, the inven