高能量光參啁啾放大器的搭建及其應用

High-energy Optical Parametric Chirped Pulse Amplifiers and Their Applications

蔡嘉倫(Chia-Lun Tsai)

指導教授 ： 楊尚達

國立清華大學/電機資訊學院/光電工程研究所/博士(2020年)

摘要

整篇文章的作者為博士班學生蔡嘉倫，他就讀於國立清華大學光電工程研究所，就學期間(2013~2020)搭建了兩種中心波長的光參啁啾放大器(OPCPA)，還有兩種不同波長的非線性雷射脈衝壓縮器。
作者在就學及研究期間，搭建了兩種光參啁啾放大器，可以放大近紅外波長雷射，以及產生中紅外光雷射。他們分別由不同的源頭雷射驅動：(1)以商用鈦藍寶石雷射放大器當作源頭幫浦雷射，自組建的光參啁啾放大器可以產生雷射脈衝1千赫茲、0.5毫焦耳、368飛秒(1.36吉瓦尖峰功率)、1.9微米中心波長。至於後級放大部分，則由摻釹釔鋁石榴石(Nd:YAG)雷射放大器作為幫浦雷射。(2)以摻鐿鎢酸釓鉀(Yb:KGW)商用雷射放大器當作源頭幫浦雷射，中心波長1.55微米的光參啁啾放大器可以產生雷射脈衝1千赫茲、3.3毫焦耳、80飛秒(41.25吉瓦尖峰功率)。這樣的光源是個強大的工具，其可應用於電子加速產生兆電子伏特動能，或是高次諧波產生極紫外光。
至於非線性雷射脈衝壓縮器，作者根據不同的雷射中心波長以及輸入脈衝能量，搭建了兩套多薄片展頻(MPC)架構去探索脈衝壓縮效果：(1)多薄片展頻架構一級，包含了9片200微米厚度的石英薄片，使得原本1.55微米中心波長的光參啁啾放大器，頻寬變成原本4倍。此頻寬經歷過脈衝壓縮之後，脈衝寬度從原本的80飛秒，壓縮變成20飛秒。(2) 多薄片展頻架構一級操作在中心波長1.03微米。光源部分來自一台自行搭建的碟片雷射震盪器，加上一套多次穿透共振腔。此光源由德國的波鴻魯爾大學提供，可產生脈衝寬90飛秒、13.4兆赫茲，以及大約10微焦耳的脈衝能量。作者協助搭建了一套多薄片展頻架構，使得雷射脈衝寬度從原本的88飛秒，壓縮變成27飛秒，轉換效率為超過90百分比。此架構建立了一個里程碑，其輸入脈衝能量小於10微焦耳，脈衝重覆率高於1兆赫茲。此架構對於未來更高脈衝能量提供了可能性，其方法為選用更為寬鬆的聚焦條件，以及色散補償反射鏡。此一短脈衝光源提供了產生軟X光源產生的條件，未來預計可以應用在無標籤的生物樣本觀察。

關鍵字

非線性光學 ； 超快光學 ； 雷射放大器 ； 光參放大器 ； 脈衝壓縮

並列摘要

In this thesis, author (Chia-Lun Tsai) focuses on introducing what he has done during his Ph. D program (2013~2020) in Institute of Photonics and Technologies, National Tsing Hua University (NTHU IPT) concerning to experimentally building two optical parametric chirped pulse amplifiers (OPCPA) and two nonlinear pulse compressors.
Two OPCPAs emitting intense near-infrared (NIR) and mid-infrared (MIR) pulses are driven by different front-end laser amplifiers: (1) With a commercial Ti:Sapphire laser amplifier as a front-end source, our first home-built OPCPA produces 1 kHz, 0.5 mJ, 368 fs pulses (1.36 GW peak power) at 1.9 µm central wavelength. A Nd:YAG laser amplifier is also used as pump laser in the rear stages. (2) With a commercial Yb:KGW laser amplifier as a front-end source, the 1.55 µm home-built OPCPA delivers 1 kHz, 3.3 mJ, 80 fs pulses (41.25 GW peak power). Such long-wavelength laser systems are powerful tools in accelerating electrons up to Mega-eV or producing coherent soft X-ray by high-harmonic generation (HHG) due to the high pondermotive force.
In terms of compression, two multiple-plate-continuum (MPC) based setups are built to explore the performances: (1) A stage of MPC consisting of 9 pieces, 200-µm-thick quartz plates broaden spectrum of 1.55 µm OPCPA pulses by four folds. After spectral phase compensation, pulse duration is compressed from 80 fs to 20 fs. (2) An MPC-based nonlinear compressor is exploit at 1.03 µm central wavelength. A home-built setup combines a thin-disk oscillator and a Multi-pass cell, provided by Ruhr-Universitat Bochum (RUB), that produces 90 fs pulse duration with 13.4 MHz repetition rate and ~10 µJ pulse energy. Author helps in MPC setup which make pulse duration from 90 fs to 27 fs with conversion efficiency >90%. The realization of low pulse energy (< 10 µJ) and high repetition rate (>1 MHz) makes a milestone on the MPC based nonlinear compressor. Energy up-scaling can be realized by using looser focusing and chirp mirrors. Such intense light source paves the way to generation of soft x-ray laser at water window for label-free bio-imaging.

並列關鍵字

nonlinear optics ； ultrafast optics ； laser amplifier ； optical parametric amplifier ； pulse compression

參考文獻

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