使用Q開關鎖模摻釹釔鋁石榴石雷射來研究 雷射誘發爆破閥值和時間的動力行為

Abstract

雷射誘發爆破現象在很多領域中已經廣泛使用，像是雷射點火、雷射誘發爆破光譜檢測樣品等。在過去，雷射誘發爆破的閥值已在很多研究中討論過。在本論文中，我們利用具有不同單發脈衝波形的Q開關鎖模Nd:YAG雷射來產生爆破。我們研究了一些穩定Q開關鎖模Nd:YAG雷射的能量波動的方法，進而探討在雷射能量、波形及峰值功率對誘發爆破閥值之影響，從而決定本實驗的雷射誘發爆破閥值。此外，我們也透過脈衝響應的概念來分析入射雷射訊號與產生的電漿訊號之間的關係。實驗結果顯示電漿訊號的響應時間約為50 ps，可推測此可能為雷射訊號要轉換成電漿能量的時間單位。最後，藉由Q開關鎖模的Nd:YAG雷射聚焦於水中，我們成功的產生直徑200 μm的微型氣泡，期望未來可以應用在微流道的研究上。

Laser-induced breakdown has been widely applied in laser ignition, laser-induced breakdown spectroscopy and so on. In the past, the threshold of the laser-induced breakdown has been explored in many researches. In this thesis, we utilize a Q-switched mode-locked Nd:YAG laser which has various temporal pulse shapes for every single pulse to induce the breakdown. We study some approaches to stabilize the energy fluctuation of this Q-switched mode-locked laser for further investigating the influences of the laser pulse shape, peak power, and energy on the air-breakdown threshold. Moreover, the relationship between the laser signal and the induced plasma has been further linked by employing the impulse response analysis. According to the experimental results, the response time is analyzed to be approximately 50 ps which corresponds to the time scale for laser energy transferring into the plasma. Finally, by focusing the Q-switched mode-locked Nd:YAG laser beam into the water, a microbubble with 200 μm in diameter can be successfully generated for further applications in microfluidics in the future.