Exploring Broad Area Quantum Cascade Lasers

Quantum Cascade Lasers fabricated for multi-transverse mode operation have seldom been investigated. And yet they exhibit curious behavior such as the coherent locking of low order modes or apparently oscillating in a single but high-order transverse mode. As opposed to the commonly used semiconductor diode laser, quantum cascade lasers are unipolar devices creating photons from electron transitions in the conduction band. This changes their inherent time scales and also leads to a very low line width enhancement factor. Thus their intrinsic performance can be substantially different than their diode counterparts. In this talk we explore a 40-micron wide broad area laser with and without feedback from an external mirror. The interest is to see if feedback can alter the transverse modes, their time scales, and if this feedback leads to nonlinear oscillations and perhaps chaos.