Mid infrared two-photon absorption in a room-temperature extended-wavelength InGaAs photodetector

We investigate the nonlinear optical response of a commercial extended-wavelength In${}_{0.81}$Ga${}_{0.19}$As photodetector. Degenerate two-photon absorption in the mid-infrared range is observed at room temperature using a quantum cascade laser emitting at $\lambda =4.5\mu$m as the excitation source. From the measured two-photon photocurrent signal we extract a two-photon absorption coefficient ${\beta }^{(2)}=0.6\pm 0.2$ cm/MW, in agreement with the theoretical value obtained from the $E_g^{-3}$ scaling law. Considering the wide spectral range covered by extended-wavelength In${}_x$Ga${}_{1-x}$As alloys, this result holds promise for new applications based on two-photon absorption for this family of materials at wavelengths between 1.8 and 5.6 $\mu$m.