脉冲激光在液体环境中的光声效应研究

发布时间：2018-04-15 03:16

本文选题：光声效应 + 脉冲激光　；参考：《哈尔滨工业大学》2015年硕士论文

【摘要】：光声效应是指物质受到脉冲光或调制光作用时产生声信号的现象,其产生的声波具有频谱宽,高空间分辨率,远距离激发,抗干扰能力强,不受检测环境限制等特点,因此已经广泛应用于工业材料的无损检测等多个领域。目前,对海洋的开发和利用已提高到国家战略要求,脉冲激光光致声波有望在海洋探测中发挥作用,已成为当今科学研究中非常有意义的工作之一。首先本文对液体及固体光声产生机制做了总结,液体的光声产生机制包括热膨胀机制、汽化机制和介质击穿机制;固体的光声产生机制包括热膨胀机制和等离子体机制。本文采用了非耦合快速热膨胀球状模型来分析液体中热膨胀机制产生声波的情况。实验部分主要运用纳秒和飞秒脉冲激光研究了不同浓度盐水以及铜、铝、碳钢等金属靶材在液体环境中受到脉冲激光激发所产生的声波信号情况。实验中通过改变激光的强度以及水听器的探测位置,观察声波信号的变化情况,并对其做了快速傅里叶变换(FFT)以获得信号频谱,进行了详细对比分析。实验发现所有实验样品产生的光声信号的强度都与激光强度成正比。其中水产生的光声信号强度沿传播方向上是以指数形式衰减的,且在低频和高频部分衰减较快。随着光强的增加,光声信号的主频向低频方向移动。不同浓度的盐水,产生的光声信号频谱存在较大差异,这主要是因为浓度改变了其光声源的结构,造成了对光的不同吸收。在特定浓度下,盐水会对激光产生共振吸收,使得到的光声信号显著增强。对于金属样品,在纳秒激光激发下的光声信号基本类似,但不同的样品有着不同的主频。三种金属样品在相同光功率的飞秒激光和纳秒激光激发下所得的光声信号存在较大差异,这说明了光声信号不仅与激光的功率有关,也与激发光源的脉宽以及峰值功率等因素相关。
[Abstract]:Photoacoustic effect refers to the phenomenon of substances by the pulse generation acoustic signal light or light modulation effect, the acoustic wave generated with wide spectrum, high spatial resolution, remote excitation, strong anti-interference ability, is characterized by the detection of environmental restrictions, so it has been widely used in industrial material nondestructive testing and other fields. At present, the development and utilization of the ocean has been raised to the national strategic requirements, pulsed laser induced acoustic waves are expected to play a role in ocean exploration, has become one of the very meaning of the scientific research work. Firstly, the liquid and solid photoacoustic generation mechanism is summarized, including the generating mechanism of liquid photoacoustic heat the expansion mechanism, mechanism of vaporization and dielectric breakdown mechanism; photoacoustic solid mechanism including thermal expansion mechanism and plasma mechanism. This paper uses the non coupling rapid thermal expansion spherical model to analyze the liquid The thermal expansion mechanism of sound waves. The experimental part is mainly using nanosecond and femtosecond of different concentration of salt and copper, laser pulse aluminum, steel and other metal target by the acoustic signal generated by pulsed laser excitation in the liquid environment. The experiment by changing the laser intensity and the hydrophone detection position, observe the change of acoustic signals, and the fast Fourier transform (FFT) to obtain the signal spectrum, are compared and analyzed in detail. The experimental results showed that the photoacoustic signal generated all the experimental samples are proportional to the intensity of the laser intensity. The photoacoustic signal intensity produced by water along the propagation direction is decays exponentially, and in the low and high frequency attenuation. With the increase of light intensity, frequency of photoacoustic signal shifts to the lower frequency. Different concentrations of salt, the photoacoustic signal spectrum generated in a The big difference, this is mainly because the structure concentration changed its light source, caused by the different absorption of light. In certain concentration, salt water will produce resonance absorption of laser, significantly enhanced the photoacoustic signal is obtained. The metal samples in nanosecond laser excitation photoacoustic signal similar. But different samples have different frequency. Three kinds of metal samples under the excitation of acoustic signals in the same optical power femtosecond and nanosecond laser has great differences, indicating that the photoacoustic signal is not only related to the laser power, and the excitation light pulse width and peak power and other factors.

【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN241

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