燃烧场中飞秒激光成丝的脉宽效应研究

发布时间：2018-01-27 10:37

本文关键词： 飞秒激光光丝阈值功率光丝诱导非线性荧光光谱燃烧诊断脉冲宽度　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：燃烧诊断为理解燃烧中复杂的化学反应过程以及提高燃烧过程能量转换效率提供实验依据。各种激光光谱诊断技术的发明,为燃烧诊断开创了新局面,其具有实时、非入侵性、高时空分辨率等优点。本文验证了利用飞秒激光成丝诱导非线性光谱的手段分析燃烧中间产物分布的可行性。在克尔自聚焦和等离子体散焦的平衡作用下,飞秒激光周期性重复聚焦和散焦过程,从而形成一条长长的等离子体通道,即光丝。飞秒激光光丝内部的超高场强足以诱导路径上的分子、原子发生离化,并产生可用于鉴别母体分子的特征性指纹荧光,所以成丝手段具有仅使用单一光源对多种燃烧中间产物同时监测的独特能力。但激光参数,如脉宽等,对光丝诱导的荧光信号的影响目前尚不完全明确,本论文以光丝诱导非线性光谱技术为基础,并重点研究了燃烧场中激光脉宽这一重要参数对飞秒激光成丝特性的影响,主要内容和结果如下:首先,我们利用飞秒激光在酒精火焰中成丝的办法,同时得到了多种燃烧中间产物的荧光光谱,并观测了脉宽对光丝诱导的酒精火焰荧光光谱的影响。实验中波长为800nm的飞秒激光经透镜聚焦至酒精灯阵列火焰中成丝,在侧向收集荧光信号。通过调整压缩机的电机位置来改变脉宽,观测各种燃烧中间产物荧光光谱变化情况。我们发现随着脉宽的增加,光谱中的各信号峰值强度随之减弱。其次,我们还观测了脉宽对飞秒激光在火焰中成丝阈值功率的影响。实验中我们利用观测焦点移动的办法成功测量了飞秒激光在酒精火焰中成丝的阈值功率,并改变激光脉宽观测成丝阈值功率的变化情况。我们发现,在火焰环境下飞秒激光成丝阈值功率随着脉宽增加而逐渐减小,这个规律和空气中得到的结果相类似。
[Abstract]:Combustion diagnosis provides experimental basis for understanding the complex chemical reaction process and improving the efficiency of energy conversion in combustion process. The invention of various laser spectrum diagnostic techniques opens up a new prospect for combustion diagnosis. It is real-time, non-invasive. In this paper, the feasibility of using femtosecond laser filament-induced nonlinear spectra to analyze the distribution of combustion intermediates is verified. Under the equilibrium of Kerr autofocus and plasma defocusing. The femtosecond laser periodically repeats the focusing and defocusing process, thus forming a long plasma channel, I. E. the ultra-high field intensity inside the femtosecond laser fiber is enough to induce molecular ionization in the path. Because of the characteristic fingerprint fluorescence which can be used to identify the parent molecule, the filament forming method has a unique ability to monitor multiple combustion intermediates simultaneously using only a single light source. However, laser parameters, such as pulse width, etc. At present, the effect on the fluorescence signal induced by optical filament is not completely clear. This paper is based on the technology of optical filament induced nonlinear spectroscopy. The influence of laser pulse width on the filamentary characteristics of femtosecond laser is studied. The main contents and results are as follows: firstly, we use femtosecond laser to filamentate in alcohol flame. At the same time, the fluorescence spectra of various combustion intermediates were obtained. The effect of pulse width on the fluorescence spectra of alcohol flame induced by optical filament was observed. In the experiment, the femtosecond laser with wavelength of 800 nm was focused through lens into the flame of wine lamp array. Fluorescence signals were collected in the lateral direction. The pulse width was changed by adjusting the motor position of the compressor, and the fluorescence spectra of various combustion intermediates were observed. We found that the pulse width increased with the increase of the pulse width. The peak intensity of each signal in the spectrum decreases. Secondly. We also observed the effect of pulse width on the threshold power of femtosecond laser filamentations in flame. We successfully measured the threshold power of femtosecond laser in alcohol flame by moving the observed focus. We find that the femtosecond laser filamentary threshold power decreases with the increase of the pulse width. This pattern is similar to that obtained in the air.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.21;TN249

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