Optically pumped lasing stimulated emission threshold

To test the suitability of MBE-grown GaN/AlGaN heterostructures for lasing, a few groups have investigated optically pumped stimulated emission [75,76], observing thresholds down to 90 kW/cm2 at 300 K. 

No well-verified Gd " laser action has been reported. Fluorescence from the lowest excited level, P7/2, occurs at 0.31 /im and terminates on the 87/2 ground state to form a three-level lasing scheme. The high threshold for three-level operation and the requirements of good host transparency and an ultraviolet source (A <0.31 /xm) for optical pumping are obstacles to obtaining stimulated emission. 

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