本文關(guān)鍵詞： 飛秒激光 光絲 閾值功率 光絲誘導(dǎo)非線性熒光光譜 燃燒診斷 脈沖寬度　出處：《吉林大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：燃燒診斷為理解燃燒中復(fù)雜的化學(xué)反應(yīng)過程以及提高燃燒過程能量轉(zhuǎn)換效率提供實(shí)驗(yàn)依據(jù)。各種激光光譜診斷技術(shù)的發(fā)明,為燃燒診斷開創(chuàng)了新局面,其具有實(shí)時(shí)、非入侵性、高時(shí)空分辨率等優(yōu)點(diǎn)。本文驗(yàn)證了利用飛秒激光成絲誘導(dǎo)非線性光譜的手段分析燃燒中間產(chǎn)物分布的可行性。在克爾自聚焦和等離子體散焦的平衡作用下,飛秒激光周期性重復(fù)聚焦和散焦過程,從而形成一條長(zhǎng)長(zhǎng)的等離子體通道,即光絲。飛秒激光光絲內(nèi)部的超高場(chǎng)強(qiáng)足以誘導(dǎo)路徑上的分子、原子發(fā)生離化,并產(chǎn)生可用于鑒別母體分子的特征性指紋熒光,所以成絲手段具有僅使用單一光源對(duì)多種燃燒中間產(chǎn)物同時(shí)監(jiān)測(cè)的獨(dú)特能力。但激光參數(shù),如脈寬等,對(duì)光絲誘導(dǎo)的熒光信號(hào)的影響目前尚不完全明確,本論文以光絲誘導(dǎo)非線性光譜技術(shù)為基礎(chǔ),并重點(diǎn)研究了燃燒場(chǎng)中激光脈寬這一重要參數(shù)對(duì)飛秒激光成絲特性的影響,主要內(nèi)容和結(jié)果如下:首先,我們利用飛秒激光在酒精火焰中成絲的辦法,同時(shí)得到了多種燃燒中間產(chǎn)物的熒光光譜,并觀測(cè)了脈寬對(duì)光絲誘導(dǎo)的酒精火焰熒光光譜的影響。實(shí)驗(yàn)中波長(zhǎng)為800nm的飛秒激光經(jīng)透鏡聚焦至酒精燈陣列火焰中成絲,在側(cè)向收集熒光信號(hào)。通過調(diào)整壓縮機(jī)的電機(jī)位置來改變脈寬,觀測(cè)各種燃燒中間產(chǎn)物熒光光譜變化情況。我們發(fā)現(xiàn)隨著脈寬的增加,光譜中的各信號(hào)峰值強(qiáng)度隨之減弱。其次,我們還觀測(cè)了脈寬對(duì)飛秒激光在火焰中成絲閾值功率的影響。實(shí)驗(yàn)中我們利用觀測(cè)焦點(diǎn)移動(dòng)的辦法成功測(cè)量了飛秒激光在酒精火焰中成絲的閾值功率,并改變激光脈寬觀測(cè)成絲閾值功率的變化情況。我們發(fā)現(xiàn),在火焰環(huán)境下飛秒激光成絲閾值功率隨著脈寬增加而逐漸減小,這個(gè)規(guī)律和空氣中得到的結(jié)果相類似。
[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.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：O643.21;TN249

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