Abstract
Significant increase in continuous wave optical power from a single quantum cascade laser (QCL), beyond its current record of 5W, will likely require power scaling with active region lateral dimensions. Active region overheating presents a major technical problem for such broad area devices. Laser thermal resistance can be reduced and laser self-heating can be suppressed by significantly reducing active region thickness, i.e. by reducing number of active region stages and by reducing thickness of each stage in the cascade. The main challenge for quantum cascade lasers with a “thin” active region is to ensure that optical power emitted per active region unit area stays high despite the reduction in active region thickness, a condition critical for the power scaling. Experimental data demonstrating a multi-watt continuous wave operation for broad area QCLs, as well as various aspects of bandgap engineering, waveguide design, and thermal design pertinent to the broad area configuration, are discussed in this manuscript. The critical differences in broad-area laser design between mid-wave and long-wave QCLs is highlighted. Finally, semi-empirical model projections showing that the goal of reaching 20W from a single emitter is realistic is presented.
