Very low threshold operation of quantum cascade lasers*
Yan Fang-Liang, Zhang Jin-Chuan†, Yao Dan-Yang, Liu Feng-Qi‡, Wang Li-Jun, Liu Jun-Qi, Wang Zhan-Guo
       
(a) The x-ray diffraction spectrum of the QCL wafers; (b) measurement of the electroluminescence spectrum (EL) pumped with a 1-μs pulse and 50-kHz repetition frequency at 25 °C.