Scaling the output power of quantum-cascade lasers with a number of cascades

Abstract

A series of quantum-cascade lasers emitting at λ≈11μm with different numbers of cascades in the active region – between 25 and 200 –grown by gas-source molecular beam epitaxy, is compared in terms of their room-temperature performance in pulsed mode as a function of the number of cascades. Within the given range of cascade number we observe a superlinear increase in both slope efficiency and differential quantum efficiency as functions of cascade number. The differential quantum efficiency scaled per number of cascades, however, shows a sublinear increase. A differential quantum efficiency of 17% per cascade and pulse power exceeding 7W per facet, both at room temperature, was demonstrated for quantum-cascade lasers with 200 cascades. All lasers with stripe width below 30μm are operated in the fundamental TEM00 spatial mode. This combination of high pulse power and TEM00 mode operation for room-temperature mid-infrared laser emission can be attractive for a number of applications.