Interferometric study of thermal dynamics in GaAs-based quantum-cascade lasers

The thermal dynamics in quantum-cascade lasers under pulsed operation is investigated by a scanning interferometric thermal mapping technique. An infrared laser beam probes the change in the refractive index caused by current-induced heating of the working devices. The measured phase shift provides a quantitative information on the thermal characteristics with a micrometer spatial and a nanosecond time resolution. Comparing the experiments with a two-dimensional thermal model enables us to determine the anisotropic heat conductivity in the multilayered active region, found to be much lower than the one of bulk GaAs, as well as the temperature increase in the active region during pulsed operation.