Observation of third order optical nonlinearity due to intersubband transitions in AlGaAs/GaAs superlattices

We report the first observations of large third order optical nonlinearities in AlGaAs/GaAs superlattices due to intersubband transitions. The process is triply resonant when the first intersubband transition matches the radiation from CO2 lasers. The intersubband relaxation time has also been estimated from the dispersion of χ(3) with the laser difference frequency Δω and found to be in good agreement with other published values. The magnitude and frequency dependence of the intersubband mechanism have been calculated using the diagrammatic technique.