| 摘要: | 1550 nm 頻段光學參量放大器，與800 nm 摻鈦藍寶石雷射放大器相比，在雷射科技方面有以下特點: (1) 種子光來源為光纖振盪器，對環境的影響較不敏感，光纖振盪器穩
定度比摻鈦藍寶石振盪器高。 (2) 光參量放大器有較高增益，可以大幅縮短整體光路。 (3) 幫浦光可以直接使用摻釹釔鋁石榴石雷射(Nd:YAG) ，不需要倍
頻。 (4) 光柵脈衝延展器與脈衝壓縮器所產生的二階、三階色散與波長成正相關，因此將中心波長移至1550 nm 有助於縮小延展器與壓縮器的體積。
然而，受限於晶體大小(磷酸氧鈦鉀, KTP) 、晶體吸收(硼酸鋇, BBO)，使得1550 nm 光學參量放大器能量受到限制。由於鈮酸鋰晶體
尺寸可超過3 吋，利用此晶體來做為1550 nm 光學參量放大器的增益介質，放大器能量得以提升，但是種子光須有角度色散來滿足相位匹配條件。在2016, György Tóth [1] 設計使用2 片光柵產生角度色散滿足匹配條件，再利用另外2 片光柵補償角度色散與空間色散。
在本論文中，我提出三等邊棱鏡架設來取代György Tóthn 所提出的雙光柵架設。首先，使用一組等邊棱鏡產生空間色散。再設計使用第三顆等邊棱鏡產生角度色散滿足放大匹配條件。並設計放大器幫浦光強度、種子光強度、相位匹配角與晶體厚度。放大後設計使用光學光柵壓縮器補償角度色散。此設計結構較為簡單，且稜鏡價格便宜。
根據數值分析模擬， 使用此新設計可望在1550 nm 頻段產生 200 mJ，脈衝寬度50 fs 的脈衝雷射，尖峰功率為4 兆瓦。在強場
雷射領域方面，由於有質動力與波長平方成正比，中心波長為1550 nm，雷射脈衝的有質動力增加為4 倍，有利於有質動力相關實驗，例如實驗室天文學、雷射加速器。;In comparison with Ti:sapphire laser amplifiers in 800 nm band, the optical parametric amplifiers (OPA) in 1550 nm band shows four the merits: (1) Erbium-doped fiber oscillator generated seed pulse is insensitive to the environment. (2) The higher gain per pass for OPA shortens the optical path. (3) Nd:YAG laser without second-harmonic generation serves as the pumping
laser. (4) The 1550-nm system shrinks the size of the grating-pair based stretcher and compressor because the second-order and third-order dispersion from the stretcher and compressor positively correlate with the wavelength.
However, the output energy of 1550-nm OPA is limited by crystal size (Potassium titanyl phosphate, KTP) and crystal absorption (Barium borate, BBO). A lithium niobate (LN) crystal as the gain media for the 1550-nm OPA system enables to enhance the output energy since the fabrication of more than 3-inch crystal size is available, but the angular dispersion of seed is critical to the phase-matching condition. In 2016, György Tóth [1] utilized a double-grating setup to generate the required angular dispersion to match the phase-matching condition, and then utilized one
more double-grating setup to compensate the spatial chirp and angular dispersion.
In this thesis, I propose a triple-prism setup to replace the György Tóth′s double-grating setup. Firstly, a prism-pair and other one prism generate a spatial chirp and the required angular dispersion for the phase-matching
condition, respectively. Secondly, the pumping intensity, seed
intensity, the phase-matching angle and the crystal length are designed for
the amplification. Thirdly, a grating-pair based compressor to compensate
the angular dispersion. Compared with György Tóth′s double-grating setup, the triple-prism setup is concise and economical.
According to the numerical simulation, this new design of 1550-nm OPA is expected to generate 50-fs pulse laser with output energy 200 mJ and peak power 4 TW. Furthermore, the ponderomotive energy is quadruple compared with the 800-nm Ti:sapphire lasers due to the double-larger wavelength. Hence, this new system of 1550-nm OPA benefits high energy
density physics, e.g. laboratory astronomy and laser acceleration. |
