A Modified “1/L Technique” for Measuring Non-Linear Gain of Quantum Cascade Lasers

Abstract

Quantum cascade lasers, first developed in 1994 and then commercialized in 2004, are used popularly in spectroscopy to detect gases and pollutants in the atmosphere, but their uses can be applied to many other fields as well. Quantum cascade lasers depend on inter-subband (within the conduction band) electron transitions to emit light rather than inter-band electron transitions. The gain of a QCL is theoretically proportional to the inverse of the length of the laser or 1/L, and this technique has traditionally been used to find the waveguide loss in these lasers. Experimental data shows that the gain does not necessarily follow this linear relationship with respect to the inverse of the length. There are two possible reasons for the discrepancies between the theory and the experiment. The first is that the gain coefficient could be dependent on the threshold current density. The second is that the This project is aimed at trying to find a different, improved approach for the 1/L technique so that experimental results match the theory more closely and so that the waveguide loss can be measured more accurately.