Low intensity saturation of an ISB transition by a mid-IR quantum cascade laser

We demonstrate that absorption saturation of a mid-infrared intersubband transition can be engineered to occur at moderate light intensities the order 10–20 kW cm−2 and room temperature. The structure consists an array metal–semiconductor–metal patches hosting judiciously designed 253 nm thick GaAs/AlGaAs semiconductor heterostructure. At low incident intensity, operates in strong light–matter coupling regime exhibits two peaks wavelengths close 8.9 μm. Saturation appears as weak regime—and therefore, single-peaked absorption—when increasing intensity. Comparison with coupled mode theory model explains data permits infer relevant system parameters. When pump laser is tuned cavity frequency, reflectivity decreases instead polariton frequencies, non-linearly increases those wavelengths, system, mimics behavior saturable mirror mid-IR range, technology currently missing.