Use of a fast ionization wave for laser pumping

Abstract

The effective laser generation depends greatly on pumping conditions. To provide fast uniform atomic or molecular levels excitation special mechanisms are often required. One of them is the use of a fast ionization wave (FIW) which gives high-excited uniform plasma due to its high propagation velocity and great values of E/p in it. In experimental works carried out at our laboratory, where we investigated both cathode and anode -directed waves, it was fo,.md dependence of ionizing wave velocity on an electrical potential of the high voltages electrode and gas pressure. There are several works in which FIW has been successfully used for laser pumping especially for lasers on self-terminated transitions. For example in our laboratory such wave was successfully applied for nitrogen laser pumping. Here investigation is focused on several phenomena in such waves and on theoretical models of FIW. The mechanism of wave propagation is closely connected with ionization processes inside the narrow structure of the wave front where the electrical field has the typical shape of solitary wave. The several models of ionizing wave are discussed. Using cross-section averaging of the basic equations a numerical code is developed for investigation of super - high velocity wave propagation. Our numerical model is based on the continuity equation for electron and on the modernized non-linear equations describing evolution of the electrical potential. Equations for electron energy and drift velocity are significantly improved. With the help of this model it is possible to investigate evolution of wave and to trace dependence of the propagation velocity, energy absorption and different atomic levels excitation on main parameters: voltage, gas pressure, radius of discharge tube, initial electron concentration. The model can be also applied to backward shock of lightning. Typical values of breakdown parameters in modeling were V=32 kV. p=l-SO ton, potential growth duration on high-voltage electrode of 10 ns.