Study on Laser Damage Threshold of Optical Element Surface Based on Gaussian Pulsed Laser Spatial Resolution

Chong, 单翀 Shan; Yuanan, 赵元安 Zhao; Xihe, 张喜和 Zhang; Guohang, 胡国行 Hu; Yueliang, 王岳亮 Wang; Xiaocong, 彭小聪 Peng; Cheng, 李成 Li

doi:10.3788/cjl201845.0104002

Cited by 4 publications

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“…For optical thin film elements in a high power laser system, when the laser acts on the optical thin film surface, the initial stage is the heat action, heat action heats the film and makes it locally heated, which leads to the increase of free electrons or gasification of the film. When the concentration of free electrons and ions reaches a certain amount, optical breakdown occurs (indicating that the optical film has undergone irreversible changes), and then the plasma is formed [1][2][3][4][5]. The absorption of subsequent laser energy by plasma causes its own temperature to rise sharply, and its volume expands outward after reaching high temperature and overheating state, that is, plasma shock wave is formed [6][7][8], and the initial propagation speed of plasma shock wave reaches the order of magnitude of -10 m s .…”

Section: Introductionmentioning

confidence: 99%

Study on the mechanism of surface pressure of optical films formed by laser plasma shock wave

Wang¹,

Su²

2023

Phys. Scr.

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In a high-power laser system, when the surface pressure of the optical film caused by laser plasma shock wave is greater than the adhesion per unit area of the film layer, the film will produce mechanical damage, and in serious cases, the whole system may not work. Therefore, studying the formation mechanism of optical film surface pressure caused by laser plasma shock wave and calculating the pressure is the key to ensure the normal operation of high power laser system. In this paper, by studying the relaxation process of shock wave on optical film surface pressure, a theoretical calculation model of shock wave on optical film pressure is established, and the variation law of pressure with different parameters is obtained, which reveals the mechanism of forming the optical film surface pressure. The calculation and simulation results show that the maximum pressure is 108 N/m2 during the laser pulse, and the pressure decreases with the increase of laser pulse time after the pulse, and the total action time of laser plasma and shock wave on the film is in the order of microseconds. The pressure increases with the increase of incident laser energy, focal length of focusing lens and incident laser pulse width, which increases with the decrease of the distance between the film surface and the focal plane of the focusing lens. The pressure changes more obviously with the incident laser energy and the distance between the film surface and the focal plane of the focusing lens than with the focal length of the focusing lens and the incident laser pulse width.

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Section: Introductionmentioning

confidence: 99%

Study on the mechanism of surface pressure of optical films formed by laser plasma shock wave

Wang¹,

Su²

2023

Phys. Scr.

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“…The resistance to laser damage of the thin film element is often evaluated by its laser-induced damage threshold (LIDT). The larger the LIDT of the thin film, the better its resistance to laser damage [3][4][5][6][7]. Therefore, how to obtain high LIDT becomes the main bottleneck to improving the resistance to laser damage of thin film components.…”

Section: Introductionmentioning

confidence: 99%

Study on the Duration of Laser-Induced Thin Film Plasma Flash

Wang

2023

Coatings

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The accuracy of judging whether the film is damaged directly affects the accuracy of the measurement of the film laser damage threshold. When judging the film damage by the traditional plasma flash method, there is a problem of misjudgment caused by the failure to distinguish the film and air plasma flash. In order to eliminate misjudgment, the two flashes are accurately distinguished by the difference in the duration of the air and film plasma flash. This paper aims to obtain the theoretical and experimental values of the duration of the film plasma flash (tf) and analyze the factors affecting it. Firstly, taking single-layer hafnium oxide and aluminum oxide thin films as examples, when the wavelength of the incident laser is 1064 nm, the diameter of the laser focusing spot is 0.08 cm, the energy of the incident laser is 100 mJ, and the pulse width of incident laser is 10 ns, the tf of hafnium oxide, and aluminum oxide thin films are 542.7 and 299.6 ns, respectively. Secondly, the experimental study of tf was carried out. Through six experiments, the following results were obtained: (1) With the increase in incident laser energy, the tf of both films increases; (2) The tf of the hafnium oxide film is longer than that of the aluminum oxide film. (3) The experimental parameters are put into the calculation model, and the theoretical results are in good agreement with the experimental tf values. Finally, it is found that tf increases with the increase in incident laser energy and incident laser pulse width, and decreases with the increase in focusing spot diameter.

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Study of the length and influencing factors of air plasma ignition time

Wang

2022

Open Physics

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When a high-energy laser acts on a film surface, plasma flashes of both the air and film can be generated simultaneously. However, when the conventional plasma flash method is used to identify thin film damage, there is a misjudgment problem caused by the inability to distinguish the air and film plasma flashes. In order to solve the problem of misjudgment, the ignition times of air and thin film plasma flashes can be obtained, respectively. If the ignition times of air and thin film plasma flashes are not equal, they can be distinguished from the time difference. In this paper, a nanosecond Nd:YAG pulse laser is used to break down the air at room temperature and pressure, and the theoretical and experimental values of the ignition time of air plasma flash are obtained. The curves of the ignition time of air plasma flash with the laser wavelength, incident energy, focusing spot, and pulse width are simulated. The reasons for the changes are analyzed from the perspectives of multiphoton absorption, cascade ionization theory, and electromagnetic theory of laser breakdown gas. The results show that when the laser pulse width is 10 ns, the energy is 160 mJ, and the spot radius is 0.015 cm. The theoretical and experimental values of the ignition time of air plasma flash are 2.146 and 2 ns, respectively, which are in good agreement. Larger values of laser focus spot size and pulse width relate to a longer ignition time of the air plasma flash, whereas larger values of laser wavelength and incident energy are related to a shorter ignition time. The research reflects the characteristics and electronic transition of air plasma, as well as the micromorphological evolution of the interaction between laser and air, presents the process of air plasma flash generation and growth, and reveals the ignition mechanism of air plasma. It not only provides a basis for improving the traditional plasma flash identification method to identify film damage but also has a certain scientific significance for studying the generation mechanism of laser-supported combustion waves and detonation waves.

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Study on Laser Damage Threshold of Optical Element Surface Based on Gaussian Pulsed Laser Spatial Resolution

Cited by 4 publications

References 0 publications

Study on the mechanism of surface pressure of optical films formed by laser plasma shock wave

Study on the mechanism of surface pressure of optical films formed by laser plasma shock wave

Study on the Duration of Laser-Induced Thin Film Plasma Flash

Study of the length and influencing factors of air plasma ignition time

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