光在随机增益介质中的放大

Optical amplification in the random gain media

结合环形腔理论,运用蒙特卡罗法模拟了光子在介质中的随机行走。研究了倍频Nd:YAG(脉宽6 ns,频率20 Hz)脉冲激光器作为泵浦光,在TiO2/若丹明B有机增益介质中,散射微粒的颗粒密度和泵浦光面积对随机激光器阈值强度的影响。模拟结果表明:随机激光阈值和光子在增益介质中的随机行走路程长度和光子通过边界返回增益区和非增益区的几率有关。随着泵浦光面积的增加,随机激光器阈值降低;增益介质中散射颗粒密度的增加降低了随机激光器的阈值。

The influence of the excitation spot area and the scatter concentration on the laser threshold were investigated in the TiO2/Rhodamine B gain media. Frequency-doubled output of a mode-locked Nd： YAG laser（20 Hz repetition rate, 6 ns pulse width） was used as the pump laser. Monte Carlo method with ring laser was used to calculate the threshold gain required for modeling the input-output characteristics in scattering gain media. The model is based on the transient two-level laser equations and includes the detailed spectral properties of the dye gain system. Monte Carlo simulation of random walks is performed in the geometry. The calculated results show that the laser threshold is related to the length of photons in gain media and the possibility of photons reflected from boundary. With the increase of the pump area, the laser threshold is decreased.