Time-Resolved Microscale Temperature Measurements of High-Power Semiconductor Lasers

Nonradiative recombination and other heat generation processes affect both the performance and lifetime characteristics of semiconductor diode lasers. This is especially true for high-power devices, where facet heating due to nonradiative recombination can lead to catastrophic optical damage (COD). Here we present for the first time temperature measurements of a semiconductor laser in which the surface temperature profile (and hence the current density profile) of the laser is measured as it evolves in time. The laser studied is a λ=1.55μm 1-cm-long InGaAsP/InP watt-class slab-coupled optical waveguide laser (SCOWL). The ridge width of the SCOWLs examined here is approximately 5 μm. Temperature measurements are taken using multiple microthermocouples with sizes less than 20μm. Surface temperature fluctuations in time are seen to be quite large, as high as 20% of the total temperature increase of the device. Time-resolved measurements allow us to see both positive correlation (in which the temperature rises at the same time across an area of the device) as well as negative correlation (in which part of the device gets hot at the same time as another part of the device gets cold). Negative correlations are likely due to facet heating processes which cause bandgap shrinkage and hence increased current flow to a facet, pulling current away from the center of the device. Time-resolved measurements of the surface temperature profile therefore show promise as a nondestructive method for characterizing the failure mechanisms of a laser, as facet damage over time is otherwise very difficult to measure before the COD runaway process destroys the device.