Continuous-wave single-mode quantum cascade laser at 5.1 THz based on graded sampled grating design

We report on the terahertz(THz)quantum cascade lasers in continuous-wave(CW)operation with an emitting frequency above 5 THz.Excellent performance with a smaller leakage current and higher population inversion efficiency is obtained by one-well bridged bound-to-continuum hybrid quantum design at 5 THz.By designing and fabricating a graded metallic sampled distributed feedback grating in the waveguide,the first single-mode THz quantum cascade laser at 5.13 THz in CW operation mode is achieved.The maximum single-mode optical power of~48 mW is achieved at 15 K with a side-mode suppression ratio above 24 dB.This will draw great interest in the spectroscopy applications above the 5 THz range for THz quantum cascade lasers.