Gain and loss measurements in gallium antimonide-based mid-infrared lasers

Considerable research effort over many years has extended the operating range of semiconductor lasers toward longer wavelengths and higher operating temperatures. Key to progress in this endeavor is a clear understanding of the optical gain and loss mechanisms and their dependence on device temperature. This work reports on gain and loss measurements made on a variety of mid-infrared GaSb-based laser samples emitting in the 2 to 4 mum range, including electrically pumped type-I lasers and three different interband type-II lasers: electrically pumped 'W' lasers, electrically pumped interband cascade lasers, and optically pumped 'W' lasers.; These type-II lasers can not currently operate in continuous wave mode at room temperature, a critical requirement for many practical applications. High temperature lasing is limited either by a decrease of maximum gain with temperature or an increase in optical loss with temperature. The experimental results described in this work indicate that gain is the limiting factor on the high temperature performance of these interband type-II lasers; the gain was found to decrease rapidly with increasing temperature, while the losses increased more slowly. This result, combined with indications that Auger recombination plays a larger than previously thought role opens up new opportunities for designing type-II lasers with superior high temperature performance.; Wide range tunability is another frontier for semiconductor lasers. The type-I lasers employed in this study employed relatively wide quantum wells, with consequently small energy steps between quantized levels. When these lasers were cleaved in to short cavity lasers with consequently high mirror losses, we observed an extremely broad and flat optical gain spectrum. These lasers are well suited for use in widely tunable external cavity laser systems.; Measurements were made using the well established Hakki-Paoli technique, and also using a newly adapted single pass technique for the optically pumped samples. The measurement of such a diverse collection of samples facilitates direct comparisons of the trade-offs associated with the different laser designs.