光抽运石墨烯太赫兹负动态电导率的理论研究

Theoretical Research of Terahertz Negative Dynamic Conductivity in Optically Pumped Graphene

石墨烯特殊的零带隙能带结构和载流子弛豫特性,在研究太赫兹辐射源相干放大领域引起广泛关注。考虑带内和带间跃迁对电导率的贡献,研究了光抽运单层和多层石墨烯中非平衡二维电子-空穴系统的动态电导率特性。结果表明,在足够强的光抽运下,石墨烯中的粒子数反转能够使得动态电导率的实部在太赫兹频段内出现负值,这使基于石墨烯的太赫兹放大或受激辐射源成为可能。同时,通过研究动量弛豫时间、温度、层数、光强对石墨烯的负动态电导率的影响表明,石墨烯多层结构的动态电导率最小值的绝对值更大,作为太赫兹激光器的激活介质更具优势。

Due to the gapless energy spectrum and carriers relaxation characteristics,graphene causes a widespread concern in amplification of terahertz coherent sources.We consider the contribution of both interband and intraband transitions to the conductivity,and study the dynamic conductivity characteristics of a nonequilibium two-dimensional electron-hole system in optically pumped single and multiple graphene layer（SGL and MGL） structures.The results demonstrate that the population inversion in graphene can lead to a negative dynamic conductivity in the terahertz range of frequencies at sufficiently strong pumping,and the phenomenon might be used in graphene-based terahertz coherent sources radiation and amplification.Meanwhile,by studying the dependences of the negative conductivity on momentum relaxation time,temperature,number of layers,and optical intensity,it is found that the minimum absolute value of the real part of conductivity in MGL structures is greater than that in SGL structures.Thus,the MGL structures have more advantages to be the active medium of terahertz laser.