光子晶体晶粒尺寸和排列结构对随机激光辐射特性的影响

The dependence of radiation characteristics of random laser on the size and arrangement of crystal grains in PCs

研究了光子晶体对随机激光器的输出特性的调控,并分析了光子晶体的晶粒尺寸和排列结构等对调控作用的影响.对于同一随机介质而言,上下表面用同种材料不同晶粒尺寸的光子晶体覆盖,结果显示:晶粒尺寸合适的光子晶体会使光在系统中来回振荡从而得到很好的放大,使系统中的光与随机增益介质的相互作用加强,激光阈值降低;同时还对激光模式有较强的调制能力,能在一定程度上抑制自发辐射,使之向所需要的频率内辐射.但如果光子晶体的晶粒尺寸与随机增益介质结构匹配不当,则光子晶体对激光模式调制能力较弱,光场能量不能有效地被局域在系统中,系统中能量消散得较快,系统需要较大的激光阈值.晶粒的排列结构对随机激光输出特性也有一定的影响.因此存在一个最佳的光子晶体/随机介质组合,使随机激光阈值达到一个极小值,为研制低阈值微型激光器提供理论依据.

The modulation on radiation characteristics of random laser caused by photonic crystals（ PCs） was studied,and its dependence on the size and arrangement of the crystal grains was analyzed. For a random medium,if it is covered by different photonic crystals on its upper and lower surfaces respectively,its output characteristics should be different. The results showed that the grain size of the PCs has a great effect on the radiation characteristics of the system. The PC with a suitable grain size plays a better role in trapping the energy in the system and it can modulate the laser modes effectively. It leads the light to oscillate back and forth,enhancing the interaction between the random gain medium and the light to achieve a greater amplification,and conseguently reducins the lasing threshold. It also controls the spontaneous emission and leads it to the target frequency in the emission spectra. However,if crystal grain size daeznot match the structure of random gain medium,the laser modes could not be modulated as we wish and the energy of the light field could not be localized effectively in the system,thus the laser system has a higher lasing threshold. The arrangement of crystal grains should affect the output characteristics also. In short,there exists an optimum PC / random medium combination for lasing,for which the lasing threshold reaches a minimum.