脈衝式近紅外人眼安全雷射研究及探討

Abstract

脈衝式人眼安全雷射在醫療、通訊、遙測、以及雷射雷達、尋標、測距等軍事領域上具有相當廣泛的應用。本文研究幾種產生人眼安全雷射的方式，一方面利用新穎的方法提昇雷射轉換效率，另一方面針對不同應用面的需求，本論文研究幾種不同架構的脈衝式人眼安全雷射的輸出特性。 (一)、利用腔內光參數共振腔技術產生數毫焦耳的高脈衝能量人眼安全雷射，並探討被動式Q開關下的雷射閾值特性以及脈衝波形受到熱效應的影響所產生的變化；(二)、使用雙端擴散鍵合的自受激拉曼散射雷射晶體，Nd:YVO4，除本身具雷射增益產生雷射之外，可自行產生受激拉曼散熱將波長轉換至1525奈米人眼安全雷射波段，並且有效降低熱累積，使得轉換效率相對一般無擴散鍵合的受激拉曼散射晶體有效提昇40%以上；(三)使用一雙包層之摻鉺/鐿離子大口徑光纖搭配新穎材料，鋁鎵銦砷量子井半導體，來作為飽和吸收體產生100毫焦耳的高能量1560奈米人眼安全雷射，除優異的散熱特性之外，更能保持高光束品質的輸出。(四)結合光纖雷射散射佳的特性、使用一大口徑摻鐿光子光纖搭配鋁鎵銦砷量子井半導體高調制深度的優點，產生高脈衝能量雷射，並使用週期性反轉鈮酸鋰晶體透過光參數共振腔產生一波長可調的人眼安全雷射，波長調整範圍超過80 奈米。(五) 使用鋁鎵銦砷量子井半導體當作雷射增益介質，透過光激發的方式以及面射型的架構下產生一高光束品質的腔外面射型雷射，並且探討由能障區激發及量子井區激發的輸出特性，在量子井區激發架構下，可有效降低熱的產生，將整體轉換效率提昇到30%以上。雷射輸出脈衝功率達500瓦。

Pulsed eye-safe lasers have drawn great interest since their wide potential in kinds of applications such as medical treatment, telecom communication, range-finder, and laser radar, etc. In this thesis, we study several schemes in realizing the NIR eye-safe lasers for different applications by employing novel materials and improving the conversion efficiency. (a). In an intracavity optical parametric oscillator (OPO), a subnanosecond ten mJ eye-safe laser was demonstrated. We theoretically and experimentally investigated the threshold of an intracavity OPO pumped by a passively Q-switched laser and the dynamics of output pulse influenced by the thermal effect in the gain medium. (b). In the configuration of self stimulated Raman scattering (SRS), we employed a double-end diffusion-bonded Nd:YVO4 crystal to decrease the accumulated heat. The performance of the self-SRS laser at 1525 nm is found to be nearly 40% higher than that with a conventional Nd:YVO4 crystal. (c). By employing an AlGaInAs semiconductor saturable absorber in a passively Q-switched Er/Yb codoped large-mode-area fiber laser, we demonstrated a passively Q-switched fiber laser at 1560 nm with output energy up to 100 μJ with high beam quality and good thermal management. (d) A passively Q-switched photonic crystal fiber (PCF) laser with an AlGaInAs saturable absorber was employed as pump source in an external-cavity OPO. By tuning the temperature of nonlinear crystal, periodically poled lithium niobate (PPLN), in the OPO, the tuning range of signal in eye-safe regime up to 80 nm was obtained. (e). An AlGaInAs QW/barrier was used as a gain medium in the external cavity surface emitting laser with high beam quality. The performance of barrier and in-well pumping schemes were investigated. The quantum defect is lower in in-well pumping and consequently the conversion efficiency is enhanced to 30% and a high peak output power up to 500 W was generated.