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. 
Marijn A. M. Versteegh and Jaap I. Dijkhuis
physics.optics cond-mat.other