Collision-induced stimulated photon echo at the transition 0-1
  The stimulated photon echo formed by the sequence of three laser excitation pulses in gaseous medium on the transition with the angular momentum change 0-1 is considered with an account of elastic depolarizing collisions. The polarization properties of this echo may be potentially interesting for the purposes of data processing. It is shown, that with the polarization of the first pulse orthogonal to that of the second and third pulses the appearance of the echo signal will be entirely determined by the action of collisions. The existence of this echo is determined by the difference in the alignment and the orientation relaxation rates of the excited level. 
V. A. Reshetov, E. N. Popov
physics.atom-ph physics.optics