Gain recovery dynamics of a terahertz quantum cascade laser

The gain recovery time of a bound-to-continuum terahertz quantum cascade laser is measured using a stimulated emission photocurrent technique. At low temperatures a value similar to 50 ps is found. This tends to decrease with rising temperature, and suggests that class B laser dynamics should be expected from these devices. Both the value and the trend in the gain recovery time are found to be consistent with hopping transport through the miniband. Power-dependent measurements of the photocurrent clearly show the effects of inhomogeneous broadening of the gain transition.