鈦藍寶石雷射中脈衝分裂與諧頻鎖模之研究

Abstract

我們以改變光線射入稜鏡的深度研究克爾透鏡鈦藍寶石被動鎖模雷射脈衝分裂與諧頻鎖模之機制。以SPM與GVD的交互作用可解釋脈衝分裂之成因﹔而諧頻鎖模則可以用增益的動態發展來解釋。此外，諧頻鎖模與脈衝分裂分別發生在脈衝峰值功率上升與下降的區段，是由於雷射閾值改變 (共振腔曲面鏡的反射率分布) 嵌制動態增益 (鈦藍寶石晶體的增益分布) 所造成的現象。另外量測到分立之光譜則是由晶體雙折射濾波和調制不穩 (modulation instability)所致。

By varying insertion of prism into the light beam to adjust group velocity dispersion (GVD), we have studied the mechanism of pulse splitting and harmonic mode-locking in a Kerr-lens mode-locked Ti:sapphire laser. We realized that the pulse splitting might result from the interaction of SPM and GVD and harmonic mode locking could be caused by gain dynamics followed by pulse splitting. In addition, the harmonic mode locking and pulse splitting occurred in the states of increasing and decreasing the pulse peak power could be explained by clamping of the gain dynamic range (gain profile of Ti:sapphire rod) by the laser threshold (cavity loss introduced by the wavelength dependent reflection the cavity mirrors). Finally, We also discovered the discrete spectral peaks in the optical spectra are results of birefringent filtering and modulation instability in the laser.