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 ͑OPIC͒ laser with a room temperature emission wavelength of 3.2 m using pump wavelength tuning to achieve resonant optical pumping. Devices with cavity lengths ranging from 312 to 2030 m are characterized to determine geometry-independent figures of merit. The measurements yield transparency pump intensities I tr that range from 230 W / cm 2 at 100 K to 7.8 kW/ cm 2 at 300 K, as gain per unit pump intensity ͑differential gain͒ 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.