Photoelectron extraction efficiency into Ar-CF₄ and Xe-CF₄ gas mixtures

Experimental measurements of the extraction efficiency f of the photoelectrons emitted from a reflective CsI photocathode into Ar-CF₄ and Xe-CF₄ gaseous mixtures are presented, as a function of reduced electric field E/p in the range 0.1 to 3 V cm⁻¹ Torr⁻¹ and as a function of CF₄ concentration. The experimental data is compared to Monte Carlo simulation results. The investigation confirms that backdiffusion of low-energy photoelectrons emitted from a photocathode into a gas medium depends strongly on the nature of the gas. The effect is especially significant in pure noble gases, but it can be considerably reduced by the admixture of certain molecular gases, like CF₄.