我們研究如何架構可滿足實用需求的短脈衝光纖雷射(脈寬約100飛秒，平均輸出功率達100毫瓦以上)。總結研究成果，在全正色散摻鐿光纖被動鎖模雷射系統中，我們認為採用核泵浦的機制比包層泵浦的機制，系統轉換效率較高，也較容易得到飛秒等級的脈衝。本論文最終採用前者的架構。泵浦在(976奈米、313毫瓦)時，可輸出平均功率為71毫瓦，脈衝重複率為23.5 MHz，頻寬為11奈米，輸出光脈衝為2.9皮秒。去線性啁啾後，脈衝寬度為212飛秒，脈衝時間-頻寬乘積為0.65，壓縮脈衝品質參量為90.2%。為提高平均輸出功率，因此雷射之高啁啾脈衝輸出較轉換極限脈衝已展延20倍，故做為種子雷射可直接放大及壓縮。我們在種子雷射腔外以及放大器之間使用帶通濾波器進行頻譜塑形，使種子光源頻譜形狀更貼近高斯形貌。經由頻譜塑形後能獲得品質較好的脈衝。放大器採用5公尺長雙包層、纖核直徑為10微米的摻鐿光纖。放大之後輸出主脈衝能量之平均功率可接近100毫瓦。利用光柵對壓縮放大後之脈衝，可獲得脈寬460飛秒及光譜半高全寬為5.2奈米，主要脈衝包含90.6%的脈衝能量，而脈衝內部結構的時間-頻寬乘積為0.67，平均功率為21毫瓦，接近高斯波形的最短脈衝。最後我們就系統改進提出建議。

We studied how to construct an ultrafast fiber laser (pulse width~100 fs, average power~ 100mW) with repetition frequency of a few tens of MHz for scientific and industrial applications. Core-pumping and cladding-pumping scheme were studied and compared. The former was formed to exhibit higher conversion efficiency and is more adaptable for femtosecond operation. The preferred configuration was found to be a core-pumped all-normal dispersion (ANDi) passively mode-locked Yb-doped fiber laser. At a repetition rate of 23.5 MHz, the laser generated an average power of 71 mW. The spectral width was 11 nm, which was able to support 142 fs-width pulses. The actual pulses were highly chirped and 2.9 ps in width. After de-chirping, the pulse duration was 212 fs. The time-bandwidth product (TBP) was 0.65, and 90.2 % of the pulse energy was in the main pulse. To generate higher power, the highly chirped pulses could be directly amplified as the TBP is sufficiently large. The scheme of spectrally shaped chirped pulse amplification was employed. The spectrum of seed laser output was shaped to be Gaussian-like. For the amplification stage, we employed a 5-meter-long double-cladding ytterbium-doped fiber with a 10 m-core. The average power after amplification was around 100 mW. After pulse compensation with a grating pair, the output power dropped to 21 mW. The spectral width was 5.2 nm, and the pulse duration was 460 fs. Approximately 90.6% of the pulse energy was in the main pulse, however. The estimated time-bandwidth product (TBP) was 0.65, which was close to that of a transform-limited Gaussian pulse. Design innovations to improve system performance were elaborated.

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