High Peak Power From Optically Pumped Mid-IR Semiconductor Lasers

We present work on the high-peak power pumping of optically pumped mid-IR semiconductor lasers. The lasers incorporated 14 type-II InAs/InGaSb/InAs quantum wells (QW). Thick quaternary absorber layers (InGaAsSb) surrounded the QWs, which allowed a large fraction of pump light to be absorbed. The devices were optically pumped with the output of a passively Q-switched Ho:YAG laser at lambda = 2.09 mu m. The Ho: YAG maximum output power was similar to 90 kW; this allows the optically pumped semiconductor lasers (OPSLs) to be pumped at several thousand times above threshold. Emission from the QW was observed near 4.1 mu m. As the pump power was increased, the QW spectra were observed to broaden and eventually saturate. Under low power pumping conditions, the OPSL pulse tracked the Ho: YAG pulse, which has a 16-ns full-width half-maximum. As the pump power was increased, the OPSL pulse duration increased and the pulse eventually split into two peaks. This may be due to a large increase in the free-carrier absorbance rates in the bulk-like quaternary absorber. Emission from the quaternary was observed near 2.2 mu m and its intensity, with respect to the QW intensity, increased significantly as the pump power was increased. This indicates that at the higher pump powers, large fractions of photogenerated carriers are reservoired in the thick absorber layers. The maximum OPSL single-ended peak power was 490 W. This is the highest reported peak power from a mid-IR semiconductor laser. A rate equation model describing the time evolution of the carriers in the QW, the stored carrier population in the reservoir, and the photon population gives good agreement with the data.