Thermal dynamic imaging of mid-infrared quantum cascade lasers with high temporal–spatial resolution

The time-resolved (TR) temperature profile of actively biased mid-infrared quantum cascade lasers (MIR QCLs) was measured by using charge-coupled-device (CCD)-based thermoreflectance microscopy (TRM) with an ultrafast temporal resolution of 50 ns and a high spatial resolution of 390 nm. Based on the measured TR two-dimensional (2D) temperature profiles, the heat generation and dissipation dynamics within the lasers have been investigated. It is found that the active-region temperature increases quickly to a peak value (up to ∼100 °C above ambient room temperature) within 500 ns upon pulsed current injection of 6 A. The heat dissipation to the top and bottom cladding layers of the device is initially comparable, yet it evolves differently with time. Within 1–2 μs, the heat dissipation to the top cladding is substantially reduced and most of the heat is drained to the substrate through the bottom cladding layer. This constrained heat dissipation results in the elevated temperature in the active region, leading to thermal quenching of lasing operation, which is confirmed by experimental light–current–voltage measurement and theoretical thermal modeling. The TRM is an enabling tool for probing internal thermal dynamics of many active electronic and photonic devices, particularly for those needing special heat and thermal arrangement.