Gain/loss device study of narrow-ridge buried heterostructure quantum cascade lasers using broadband infrared transmission

Narrow-ridge buried heterostructure quantum cascade lasers (QCL) were investigated using mid-infrared (mid-IR) transmission spectroscopy at the IR beamline of the Swiss Light Source (SLS). The notable advantage in brilliance of such a synchrotron source compared to that of a Globar (typically a factor of 100) means that high-resolution broadband transmission spectra for the analysis of the gain coefficient at constant waveguide core temperature can be taken. This represents an important extension of transmission studies on working single mode QCL devices, for the determination of key laser parameters.