Ultrafast all-optical shutter based on two-photon absorption.

An ultrafast all-optical shutter is presented, based on a simple two-color, two-photon absorption technique. For time-resolved luminescence measurements, this shutter is an interesting alternative to the optical Kerr gate. The rejection efficiency is 99%; the switching-off and switching-on speeds are limited by the pulse length only; the rejection time is determined by the crystal slab thickness; and the bandwidth spans the entire visible spectrum. We show that our shutter can also be used for accurate measurement of group velocity inside a transparent material.