Improving discharge-initiated HF/DF lasers using chain reaction

A few years ago, it has been demonstrated that the use of hydrocarbons such as C 2 H 4 or C 6 H 12 as hydrogen donor allows realizing high-volume discharges in SF 6 based non-chain HF/DF gas mixture. Although high energy, short pulses and high repetition rates have been obtained, for some uses the specific output energy, the efficiency and, to a less extent, the optical quality of all these lasers remain insufficient. IT appears now that the only way to increase these values is to use chain reaction. But chain reaction is known to be delicate to control, especially when working at high repetition rate. This paper will describe recent work directed towards a better understanding of the discharge mechanisms and an increase of the efficiency and of the specific output energy of HF/DF pulsed lasers using chain reaction in discharge initiated repetitive and non-repetitive experiments. High volume discharge cells compatible with repetition rate have been realized. Discharge initiated repetitive chain reaction ash been studied up to 10Hz with large gap. Efficiencies as high as 70% have been obtained in single pulse experiments. Computer modeling allows now predicting satisfactorily the performances of discharge-initiated chain reaction HF/DF lasers as a function of electric circuit characteristics and gas composition.