高重覆率全固態人眼安全雷射研究

Abstract

波長1.5~1.6μm的脈衝式人眼安全雷射在雷射遙測和雷射測距儀等相關應用上是不可或缺的。高重覆率(＞10kHz)高尖峰功率(＞1kW)的雷射，有助於提升應用系統的效能，而光學參數振盪器(OPO)雷射能具有這一特性。在論文裡以摻釹釩酸釔(Nd3+:YVO4)和鈦氧磷酸鉀(KTP)晶體為研究主體，使用1064nm左右的Nd3+:YVO4雷射激發以KTP晶體為主的OPO可以產生波長在1.57μm附近的人眼安全固態雷射。分別採用聲光晶體、可飽和吸收體作為Q-開關元件(Q- switcher)，實現高轉換效率的主、被動式Q-開關脈衝型雷射系統。首先，我們完成一個採用聲光晶體Q-開關雷射二極體激發式Nd3+:YVO4/腔內OPO雷射系統，可以工作在10-80kHz高脈衝重覆率。進一步研究腔內OPO雷射輸出的最佳化，而獲得更高的功率輸出。在激發功率15W，脈衝重覆率80kHz時，1573nm平均功率可高於1.5W，尖峰功率高過2kW。接著，改採用Cr4+:YAG吸收晶體設計製作一套結構小巧的高功率被動式人眼安全固態雷射，再藉由考慮晶體熱透鏡效應以及調整光模與激勵光束匹配條件，從而提升在1573nm波長輸出功率。在輸入功率15W時，訊號脈衝重覆率高於50kHz，平均輸出功率1.5W以上，尖峰功率高於5kW。

1.5–1.6μm wavelength pulsed eye-safe lasers are indispensable for applications such as telemetry and range finders. High-peak-power (> 1 kW) laser with a high repetition rate (>10 kHz) is beneficial to the performance of these application systems. In this thesis, we take the optical parametric oscillator (OPO) approach to accomplish a serial of high-repetition-rate high-power eye-safe lasers and investigate the optimization of output power. First, we used KTP crystal to develop an intracavity OPO laser excited by a diode- pumped acousto-optically (AO) Q-switched Nd3+:YVO4 laser, which could be operated at high repetition rate up to 80 kHz,and higher output power was achieved by optimization of the intracavity OPO laser output coupler. With an absorbed pump power of 15W, pulse repetition rate of 80 kHz, its average output powers at 1573nm was above 1.5W and peak powers was higher than 2 kW. Second, we demonstrated a compact 2.5W-excited high-peak-power passively Q switched eye-safe solid-state laser, by using Cr4+: YAG saturable absorber. Furthermore, by taking the crystal thermal lensing effect into consideration and matching the optical mode and pump beam size, we scaled up the 1573 nm output power. With an incident pump power of 15 W, the compact intracavity OPO cavity produced average output power at 1573 nm .up to 1.5 W and peak powers higher than 5 kW with pulse repetition rate above 50 kHz.