薄膜损伤的等离子体冲击波特征研究

发布时间：2018-06-05 23:58

本文选题：激光薄膜 + 激光损伤　；参考：《西安工业大学》2017年硕士论文

【摘要】：随着科学技术的不断发展,光学系统的应用领域越来越广泛,光学薄膜作为光学系统中的核心组成部分越来越受到重视,其主要作用是调控光束传输质量,保护系统以免发生损坏。然而在强激光作用下,光学系统中的薄膜不可避免会发生损伤,一旦损伤发生将会影响整个系统的功能。衡量薄膜稳定性最重要的参数就是薄膜的抗激光损伤阈值,而激光对薄膜损伤主要是以等离子体冲击波的形式造成的,因此研究等离子体冲击波的特征就具有重要意义。本文在理论研究基础上,选购了一套等离子体冲击波采集和处理设备,搭建了实验平台,分别对等离子体冲击波在空气中的传播规律、衰减规律、频域特征以及其与激光辐照能量之间的关系进行了实验分析,并最终得到了以等离子体冲击波强度特征为判别依据的薄膜损伤阈值测试方法。将传声器置于冲击波场中的不同位置,以相同条件多次辐照薄膜样片,可以得到冲击波在不同位置的特征规律;改变传声器与辐照点距离,测得激光器输出脉冲时间与等离子体冲击波传播到传声器的时间,可以得到等离子体冲击波在固定距离下的传播马赫数;改变激光脉冲能量,在固定的位置采集等离子体冲击波信号,分析信号的强度与频域信息,可以得到二者与激光辐照能量间的关系;根据激光辐照能量与等离子体冲击波强度关系,结合薄膜损伤情况,可以得到以等离子体冲击波为特征的薄膜损伤判别方法。实验表明:等离子冲击波在空气中以近似球面的形式传播,其传播马赫数会迅速衰减,当到达厘米量级时,速度便已衰减为声速;等离子体冲击波的频率会随着激光辐照能量的增加而降低,而其强度会随着激光辐照能量的增加而增大;根据薄膜的激光损伤阈值与冲击波强度和激光能量的关系式中,可以计算出以等离子体冲击波强度为特征的薄膜损伤判别标准,经实验验证,该方法准确度高,识别快速,具有很好的应用前景。
[Abstract]:With the development of science and technology, the application of optical system is more and more extensive. Optical thin film, as the core component of optical system, is paid more and more attention to, and its main role is to control the quality of beam propagation. Protect the system from damage. However, the thin film in the optical system will inevitably be damaged under the strong laser irradiation. Once the damage occurs, the function of the whole system will be affected. The most important parameter to measure the stability of the film is the threshold of laser damage, which is mainly caused by plasma shock wave, so it is of great significance to study the characteristics of plasma shock wave. On the basis of theoretical research, a set of equipment for the acquisition and treatment of plasma shock wave has been selected, and an experimental platform has been set up to study the propagation and attenuation of the plasma shock wave in the air, respectively. The characteristics in frequency domain and the relationship between them and the energy of laser irradiation are analyzed experimentally. Finally, the damage threshold testing method based on the characteristics of plasma shock wave intensity is obtained. When the microphone is placed in different positions in the shock wave field and the film sample is irradiated with the same conditions many times, the characteristic law of the shock wave at different positions can be obtained, and the distance between the microphone and the irradiation point can be changed. By measuring the laser output pulse time and the time when the plasma shock wave propagates to the microphone, the Mach number of the plasma shock wave propagating at a fixed distance can be obtained, and the laser pulse energy can be changed. The relationship between the intensity and frequency domain information of the plasma shock wave signal and the laser irradiation energy can be obtained according to the relationship between the laser irradiation energy and the plasma shock wave intensity, and the relationship between the laser irradiation energy and the plasma shock wave intensity can be obtained by collecting the plasma shock wave signal at a fixed position. Considering the damage of the film, a method for judging the damage of the film, which is characterized by the plasma shock wave, can be obtained. The experimental results show that the plasma shock wave propagates in the form of an approximate sphere in the air, and its Mach number will decay rapidly, and when it reaches the centimeter level, the velocity has been reduced to the velocity of sound. The frequency of plasma shock wave will decrease with the increase of laser irradiation energy, and its intensity will increase with the increase of laser irradiation energy, according to the relation between laser damage threshold and shock wave intensity and laser energy, The damage criterion of film characterized by the intensity of plasma shock wave can be calculated. The experimental results show that the method is accurate, rapid and has a good prospect of application.
【学位授予单位】：西安工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O484

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