利用腔內繞射耗損探討被動式Q開關 Nd:YAG脈衝雷射的消尾現象

Abstract

毫焦耳級的脈衝式雷射在眼科的領域已經是相當成熟的技術，應用也已經相當普遍。在本論文，利用閃光燈當幫浦光源，再藉由摻銣釔鋁石榴石當作增益介質且搭配Cr4+:YAG 飽和吸收體作為Q開關，共振腔部分以一平凸透鏡作為前鏡再以一凹凸透鏡作為輸出鏡搭配成一不穩定共振腔並利用熱透鏡效應使共振腔達到穩定的狀態，而共振腔長度為90 mm。本實驗藉由數組不同曲率半徑的前鏡和輸出鏡作排列組合式的搭配，量測雷射的總輸出能量和雷射誘發空氣爆破閥值，並利用示波器量測雷射訊號波形，再接著探討雷射訊號波形和雷射誘發空氣爆破閥值之間的關聯性。

The technique of pulsed pumping millijoule laser is well-developed in ophthalmology field and the related application. In this thesis, we utilize flash-pumped source to excite the Nd:YAG crystal and insert Cr4+:YAG to be the satuable absorber as forming the Q-switched operation. The cavity is set by a plano-convex mirror and concave-convex mirror, which is an unstable cavity with 90-mm-long cavity length. We measure the total output energy, laser-induced air breakdown threshold energy and laser output signal in time domain by exploiting different combinations of the radius of curvature of front mirrors and output couplers. We demonstrate the experimental results and explain the relationship between the cavity mirrors and the threshold energy through the output pulse shape in temporal domain