Highly power-efficient quantum cascade lasers

Quantum cascade lasers 1 are promising mid-infrared semiconductor light sources for molecular detection in applications such as environmental sensing or medical diagnostics. For such applications, researchers have been striving to improve device performance 2 . Recently, improvements in wall plug efficiency have been pursued with a view to realizing compact, portable, power-efficient and high-power quantum cascade laser systems 3 , 4 . However, advances have largely been incremental, and the basic quantum design has remained unchanged for many years, with the wall plug efficiency yet to reach above 35%. A crucial factor in quantum cascade laser performance is the efficient transport of electrons into the laser active regions. We recently theoretically described this transport process as limited by the interface-roughness-induced detuning of resonant tunnelling 5 . Here, we report that an ‘ultrastrong coupling’ design strategy overcomes this limiting factor and leads to the experimental realization of quantum cascade lasers with 40–50% wall plug efficiency when operated in pulsed mode at temperatures of 160 K or lower. A quantum cascade laser with a wall-plug efficiency of up to 50% is experimentally realized when operated at low temperatures and in pulsed mode. The high-efficiency performance is achieved by implementing an ultrastrong coupling between the injector and active regions.