Microthermography of diode lasers: The impact of light propagation on image formation

We analyze the effect of propagating infrared thermal radiation within a diode laser on its thermal image taken by a thermocamera. A ray-tracing analysis shows that this effect substantially influences image formation on a spatial scale of 10 μm, i.e., in the domain of microthermography. The main parameter affecting the thermal radiation spread in the semitransparent semiconductor structure is the free carrier concentration in the substrate, governing its absorption. Two applications are presented: a quantum dot laser and a quantum-well laser, where independent thermal models are developed using the finite element method (FEM). Our ray-tracing analysis verifies the FEM simulated temperature profiles by interlinking them to experimental temperature maps obtained through microthermography. This represents a versatile experimental method for extracting reliable bulk-temperature data from diode lasers on a microscopic scale.