增益随机散射介质中的非相干辐射

用蒙特卡罗方法仿真了增益随机散射体中的非相干辐射，观察了非相干随机激光的特性。当抽运能量超过一定阈值时，散射体的整体辐射谱突然变窄；随着抽运能量继续增大，在光滑谱背景上会出现分离尖峰；散射体内空间某位置处频率组成不是单一的；辐射谱中某单个频率的空间方向分布和位置分布比较广。增益随机散射体中产生的非相干随机激光本质上既不同于无反馈的普通放大自发辐射，又不同于相干反馈形成的常规激光。解释了非相干随机激光辐射谱上出现分离尖峰的原因，出现这种现象是由于少数光子在增益散射体中经历较多次数散射后得到了相对充分的放大。

Incoherent radiation of amplifying random media is investigated using Monte Carlo simulation and the characteristics of random laser are observed. The entire emission spectra of random media become narrow abruptly when pumping energies exceed certain threshold values, and when the pumping energies further increase, distinct sharp peaks emerge on spectrum background. The intensity of a certain spatial point within the scattering media is contributed from emissions of many frequencies. And the intensity of single frequency of the entire spectrum is contributed from emissions with wide spatial and angle ranges. It has been pointed out that the incoherent radiation of amplifying random media is essentially different from amplified spontaneous emission without any feedback as well as conventional resonant-feedback laser. The explanation on distinct sharp peaks is that rare photons have experienced rather more scattering events and longer paths in amplifying random media, and these photons accumulate more gain.