Low power saturation of an ISB transition by a mid-IR quantum cascade laser
Résumé
We demonstrate that absorption saturation of a mid-infrared intersubband transition can be engineered to occur at moderate light intensities of the order of 10-20 kW.cm$^{-2}$ and at room temperature.
The structure consists of an array of metal-semiconductor-metal patches hosting a judiciously designed 253~nm thick GaAs/AlGaAs semiconductor heterostructure. At low incident intensity the structure operates in the strong light-matter coupling regime and exhibits two absorption peaks at wavelengths close to 8.9 $\mu$m. Saturation appears as a transition to the weak coupling regime - and therefore to a single-peaked absorption - when increasing the incident power. Comparison with a coupled mode theory model explains the data and permits to infer the relevant system parameters.
When the pump laser is tuned at the cavity frequency, the reflectivity decreases with increasing incident power. When instead the laser is tuned at the polariton frequencies, the reflectivity non-linearly increases with increasing incident power. At those wavelengths the system therefore mimics the behavior of a saturable absorption mirror (SESAM) in the mid-IR range, a technology that is currently missing.
Origine | Fichiers produits par l'(les) auteur(s) |
---|---|
Licence |