Influence of a time delay between a prepulse and the main discharge pulse on the characteristics of an electric-discharge XeCl laser

The results are given of an experiment in which the active mixture of an XeCl laser was excited in the following sequence: preionization, prepulse, main discharge. The mixture was preionized by ultraviolet radiation from an array of sparks through a planar grid electrode. The mixture consisted of Ne (He), Xe, and HCl at pressures of respectively 2.2 atm, 6 Torr, and 0.6 Torr. A study was made of the influence of the time delay τ of the main discharge pulse, relative to the prepulse, on the laser characteristics. For zero time delay, the laser spot was a 4 X 2.5-cm rectangle. For τ > 100 ns, a marked reduction was observed in the laser pulse energy; lasing ceased in the center of the beam and the beam was split into two luminous bands whose separation widened as τ was increased. The observed change in the intensity profile was well described by a model allowing for the inhomogeneous distribution of the vibrationally excited HCl molecules (ν = 1, 2, 3, ...) formed after the passage of the prepulse. The rate of attachment of electrons to HCl (ν = 1, 2, 3, ...) molecules was two orders of magnitude higher than that to unexcited molecules, so that the electron attachment processes were considerably faster in the center of the discharge region than at its edges. Numerical estimates were made. A comparison of the experimental with the calculated dependences demonstrated a good qualitative agreement. The possibilities for using the observed phenomenon in practice were analyzed.