High-temperature and high-power operation of terahertz quantum-cascade lasers

Abstract

We summarize recent development of terahertz quantum-cascade lasers (QCLs) based on a resonant-phonon active region design and metal-metal waveguides for mode confinement. Maximum pulsed operating temperature of 169 K is demonstrated for a 2.7 THz design. Lasers processed with the semi-insulating surface-plasmon (SISP) waveguides and the metal-metal (MM) waveguides are experimentally compared. Whereas the SISP waveguides have higher out-coupling efficiencies, the MM waveguides demonstrate improved temperature performance owing to their lower-loss and near unity mode confinement; however, this comes at the cost of poor radiation patterns and low output power. The beam quality and the out-coupling efficiency of the MM waveguides is shown to be significantly improved by abutting a silicon hyperhemispherical lens to the cleaved facets of ridge lasers. Whereas peak pulsed power of 26 mW at 5 K was detected from a 4.1 THz laser without the lens (device <i>T_max</i> = 165 K), the detected power increased to 145 mW with the lens with only a 5 K degradation in the maximum operating temperature (device <i>T_max</i> = 160 K).