RIKEN Center for Advanced Photonics, THz Quantum Device Team, 519-1399 Aramaki-aza Aoba, Aoba-ku, Sendai, 980-0845, Japan.
School of Electronics Science and Engineering, Nanjing University, 163 Xianlin Street, Qixia District, Nanjing, 210046, China.
Sci Rep. 2022 Dec 23;12(1):22228. doi: 10.1038/s41598-022-25139-9.
The recent designs of terahertz quantum cascade lasers usually employ the short periodic length and also the tall barriers for high-temperature operation. In this work, the effect of high-energy lying non-relevant subbands is studied based on nonequilibrium Green's function formalisms model, demonstrating those subbands are probable to play a minor role on the population inversion, but play a major role on the optical gain at high temperatures. The phenomenon can be ascribed to the appearance of leakages crossing neighboring periods via sequential resonant tunneling, and those leakages are inherently created by the specific features of the two-well configuration in this design that the phonon well should be wide enough for performing the phonon scattering to depopulate the lower-laser subband. The narrower periodic length design can strengthen this inter-period leakage. A parasitic absorption between the first high-lying nonrelevant subbands from two laser wells can closely overlap the gain shape and thus significantly reduce the peak gain.
太赫兹量子级联激光器的最新设计通常采用短周期长度和高的势垒来实现高温操作。在这项工作中，基于非平衡格林函数理论模型研究了高能非相关子带的影响，结果表明这些子带可能对粒子数反转的影响较小，但对高温下的光增益有较大的影响。这种现象可以归因于通过顺序共振隧穿，相邻周期之间的泄漏的出现，而这些泄漏是由设计中双势阱结构的特点所固有产生的，即声子阱应该足够宽以进行声子散射来耗尽下激光子带。较短的周期长度设计可以增强这种周期间的泄漏。来自两个激光阱的第一个高能非相关子带之间的寄生吸收可以与增益形状紧密重叠，从而显著降低峰值增益。
