Gain And Loss In An Optically Pumped Mid Infrared Laser

We report on measurements of the temperature dependence of the gain and internal waveguide loss of a 3.4 micrometers, optically pumped InAs/InGaSb, type II, W laser. A high-resolution Fourier Transform Infrared (FTIR) spectrometer was used to measure the laser mode spectra below threshold. To obtain an accurate determination of the gain, a full curve fit to the spectral output of the Fabry-Perot cavity was utilized. Our results indicate very low waveguide loss (a = 2 /cm) at 78 K, with no apparent increase up to at least 120 K. Additional measurements of the gain properties of the device reveal a rapidly decreasing differential gain, dG/dP and a rapidly increasing transparency pump power with increasing temperature. Moreover, measurements of the peak gain at constant pumping show a rapid decline with increasing temperature. Theoretical superlattice empirical pseudopotential model (SEPM)-based calculations suggest that the substantial differences between the conduction and valence subband in-plane curvatures contribute to the rapid decline in gain with increasing temperature.