High-power short-wavelength quantum cascade lasers

We describe the design and implementation of a broad-gain and low-threshold (Jth = 860 A/cm2 at 8 K) quantum-cascade laser based on strain-compensated In0.73Ga0.27As-AlAs on InP. Laser emission between 3.7 and 4.2 um is achieved because of the very large Gamma-valley conduction band discontinuity with narrow quantum wells, allowing large intersubband energy differences. Furthermore, the design inhibits carrier loss from the upper lasing state into the continuum even at elevated operating temperatures, resulting in room-temperature operation. Laser operation in pulsed mode is achieved up to a temperature of 330 K with maximum single-facet output peak powers of 6 W at 8 K and 240 mW at 296 K. The temperature coefficient T0 is 119K. The 30-period structure exhibits an external differential efficiency of 13 (40% per period) at low temperatures and a maximum wall-plug efficiency of 24%. The lasing transition takes place from several upper states to several lower states, resulting in a relatively broad (300 cm-1) gain spectrum and could allow the design to be used in external tuning configurations.