在光譜學以及顯微術的應用中，可調整波長的超快雷射是一項非常重要的工具。在這項研究中，我們利用在一塊週期性極化晶體中進行的光學參數放大技術(optical parametric amplification, OPA)，完成了一套從700奈米到1900奈米的可調式雷射光源。光學參數放大需要一個泵浦光源(pump)跟一個種子光源(seed)。在這套系統中，泵浦光源是來自於倍頻過後的鐿-光纖雷射，而經過倍頻晶體後剩下的未經倍頻雷射則被回收導入一條光子晶體光纖(photonic crystal fiber, PCF)中，用以產生超連續光源(supercontinuum)，作為光學參數放大中所需的種子光源。與傳統的光學參數放大相較，這套系統避免了泵浦光源與種子光源之間的時序劇跳現象(timing jitter)。再加上我們採用了雙種子機制，以及高效率晶體(週期性極化鈮酸鋰)，這些就是我們的系統有高效率的原因。在每個脈衝只有10奈焦耳的情況下，我們得到了超過百分之四十的轉換效率。再搭配50 MHz的高重複率，使得這套系統可以做為一個非常適合生物醫學及顯微術應用的理想光源。除此之外，值得一提的是，在這麼高的重覆率之下，這是目前已知的單程光學參數放大中，最高的轉換效率。

Tunable ultrafast light sources are important for various spectroscopic and microscopic applications. We have demonstrated a 700 nm – 1900 nm wavelength-tunable light source based on a single-pass optical parametric amplification (OPA) in a multi-period magnesium oxide doped periodically poled lithium niobate (MgO:PPLN) crystal. The OPA pump was a frequency-doubled ultrafast ytterbium-doped fiber laser and the residual laser power after frequency doubling was recycled to generate a supercontinuum seeding source in a photonic crystal fiber. Compared with conventional OPAs, this system is free from timing jitter between the pump and the seed. Combined with the double seed scheme and the high efficient crystal, PPLN, these are responsible for the high conversion efficiency. Over 40% conversion efficiency was obtained with 10 nJ pump energy. Combined with a 50 MHz repetition rate, this versatile source is ideal for biomedical and spectroscopic applications. Moreover, this is the highest single-pass OPA efficiency at such high repetition rate.

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