Kinetic model of the sustained discharge excitation of the cadmium mercury excimer

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Abstract
The results of a theoretical investigation of the discharge excitation of the CdHg* excimer are presented. Estimates are obtained for the efficiency of production of CdHg*, which has potential as an energy‐storage medium for the amplification of light pulses at 470 nm. A time‐independent analysis using a Boltzmann code was performed on a Cd, Hg mixture with an argon buffer. Seven atomic levels were considered in both Cd and Hg. A very high efficiency is obtained for excitation of the Cd(3P0,1,2) manifold from which the CdHg* excimer forms. The optimum E/N value for the mixture Cd : Hg : Ar=1 : 4 : 20 is 8×10−17 V cm2. The small value of the calculated Townsend coefficient at this E/N value required the consideration of an electron beam as the primary source of ionization. A detailed kinetic model was constructed which included electronic transition rates three‐body association rates, dissociative recombination, biexcimer mixing, and biexcimer quenching. The kinetic equations were solved using the time‐dependent solution of the Boltzmann equation for the electronic distribution function with a source term to account for the production of slow secondary (∼1‐eV) electrons by ionization collisions of the fast (∼100‐keV) primary electrons from the sustainer electron beam with the neutral atoms of the gas mixture. The effects of superelastic and inelastic collisions were explicitly included in the evaluation of the distribution function. In the case of a Cd : Hg : Ar mixture of 1 : 4 : 20 and Cd density of 5×1017 atoms/cm3, 40% of the discharge energy was deposited after 1 μsec into the molecular manifold of CdHg*. The sustainer ionization rate was 3.61×1020 electrons/cm3/sec, and the E/N value was 8×10−17 V cm2. The stored‐energy density was 7 J/l. A molecular potential diagram for CdHg is given which indicates that 50% of the stored energy could be available for the amplification of subnanosecond optical pulses at 470 nm.