High-performance 5.5 4;μm quantum cascade lasers with high-reflection coating

A high-reflection coating for 5.5 4;µm strain-compensated InGaAs/InAlAs quantum cascade lasers is described. Using a high-reflection coating on both facets of a laser cavity, a threshold current density of 0.5 4;kA/cm2 was observed at liquid-nitrogen temperature, whereas for an uncoated structure of comparable length the threshold current density was 1 4;kA/cm2. Laser action for a 2.1 4;mm long and 30 4;µm wide device with coated facets was achieved in pulsed mode up to the record high temperature of 470 4;K. A 2.5 4;mm long and 30 4;µm wide device with uncoated facets shows lasing action up to 440 4;K.