Nonlinearity and response speed evaluation of intersubband transition in InGaAs/AlAsSb quantum well

We report the first reliable estimate of the saturation intensity in InGaAs/AlAsSb quantum wells using the homogeneous linewidth estimated from a careful lineshape analysis of the absorption spectra recorded as a function of temperature and the pump-probe relaxation time (τ≈2.1 psec) at room temperature. The estimated value of saturation intensity is 52±5 MW cm² at an excitation wavelength of 1.92 μm. We performed a direct saturation measurement to estimate the linear absorption coefficient (α₀) and the 3rd order susceptibility (χ⁽³⁾). We observed a giant χ⁽³⁾ of about 8.2×10^-15 m²/V ². The linear absorption coefficient is evaluated to be 3370 cm^-1. From these values we estimated the figure of merit to be 1.2×10^-8 m³ V^-2s^-1 in this material