Transparency pump intensity and differential gain in resonantly pumped W optical pumping injection cavity lasers

Abstract

We report the results of a cavity length characterization of a W optical pumping injection cavity (OPIC) laser with a room temperature emission wavelength of 3.2 μm using pump wavelength tuning to achieve resonant optical pumping. Devices with cavity lengths ranging from 312 to 2030 μm are characterized to determine geometry-independent figures of merit. The measurements yield transparency pump intensities Itr that range from 230 W/cm2 at 100 K to 7.8 kW/cm2 at 300 K, as gain per unit pump intensity (differential gain) decreases from 0.17 cm/W at 100 K to 0.011 cm/W at 300 K. The characteristic temperature of the transparency pump intensity is 55.6 K, while the gain per unit pump intensity demonstrates an exponential decay with a characteristic temperature of 67.9 K. Compared to other optically pumped type-II W lasers and electrically injected interband cascade lasers, there is less reduction in the differential gain with increasing temperature, consistent with the high temperature operation of these OPIC devices.