LT-GaAs detector with 451fs response at 1.55 mu m via two-photon absorption

The impulse photoresponse from low temperature (LT) grown GaAs coplanar str ipline switches was measured at 1.55 mu m using double sliding-contact samp ling. The response was attributed to two-photon absorption as confirmed by the observed quadratic dependence of the photocurrent on average incident i llumination. The devices exhibited a response full width at half maximum of 451fs and a 3dB bandwidth of 190GHz, which is, to date, the fastest respon se measured from LT-GaAs switches at this wavelength. The response peak was linearly dependent on the applied bias and showed a strong dependence on i ncident field polarisation. These devices could find applications in high t emporal resolution sampling at 1.55 mu m.