利用基因演算法還原虛光闌克爾透鏡鎖模雷射的超快波形和相位

Abstract

克爾透鏡鈦藍寶石被動鎖模雷射通常藉由自相位調變與群速色散(GVD)間的交互作用而產生超短脈衝雷射。有時我們在鈦藍寶石雷射中可觀察到小於1ps的脈衝分裂，因為GVD未能完全補償，而在脈衝前緣及後緣會有非線性啾頻產生。此外，多脈衝間的不對稱間距也被報導。為了要了解這些現象發生的原因，我們必須知道相位隨時間的變化。我們使用了單雙光子自相關器及基因演算法去計算相位。基因演算法是一種非限制的數學最佳化理論，它是依照生物學中的“適者生存”進化理論所發展出來的。基因演算法由三個運算子：選擇、交配、突變來尋找最佳近似解。 透過相位回溯，我們可知克爾透鏡鈦藍寶石鎖模雷射中脈衝分裂的啾頻。它同時顯示了因為GVD未能完全補償脈衝前後緣的非線性啾頻，以致於造成脈衝分裂。

A Kerr-lens mode-locking (KLM) laser usually relies on soliton-like pulse shaping effect from interplay between the self phase modulation (SPM) and the group velocity dispersion (GVD) to generate ultra-short pulses. Sometimes, nonlinear chirp generated in the leading and trailing edge of pulse could not be fully compensated by GVD and then the pulse splitting below 1ps was observed in Ti:sapphire laser. Besides, another kind of multiple pulses with nanosecond asymmetric spacing between pulses was also reported. To understand the reason why these phenomena occurred, chirp is the most important information needs to know. Thus we use two and one interference autocorrelator and make use of Genetic Algorithms (GA) analysis to calculate phase of pulse. GA is one of the non-constrained mathematical optimization theories based on the evolution theory in the biology (survival of the fitness). It finds a near-global optimization solution based on four steps including encode, selection, crossover, and mutation. Through the phase retrieval, the chirp of pulse splitting in a Kerr-lens mode-locked Ti:sapphire laser were investigated. It also shows nonlinear chirp generated in the leading and trailing edge of pulse could not be fully compensated by GVD is the cause of pulse splitting.