VUV generation in hydrogen and fluorine in diffuse discharges produced by runaway electrons

We study parameters of stimulated emission in diffuse discharges formed in a sharply inhomogeneous electric field in mixtures of inert gases with additions of hydrogen and fluorine at pressures up to 10 atm. Efficient VUV lasing is obtained on molecular transitions of hydrogen at 148–161 nm and fluorine at 157 nm. It is shown that the addition of helium and neon buffer gases increase the pulse duration and output energy of a H₂ laser. A laser pulse duration of over 10 ns is obtained at a radiation energy of 0.1 mJ. It is found that in mixtures of He with F₂ the diffuse discharge is formed by successive ionisation waves. The generation pulse at 157 nm is shown to have three peaks, which correspond to the maxima of the diffuse discharge current. Depending on the composition and the mixture pressure, the first or second generation peak has a maximum intensity. At a mixture pressure of 10 atm, the maximum generation efficiency of a F₂ laser is 0.18%, which exceeds the efficiency of lasers of this type pumped by transverse volume discharges with preionisation from an additional source.