Cryogenic Pulsed Laser Deposition of Lithium for $^{4}$He Absorption Experiments

We are developing techniques to prepare films of alkali metals on cryogenic surfaces by laser ablation. The alkali metals are known to provide weak adsorption potentials for $^{4}$He which results in nontrivial wetting and superfluid onset phenomena. Film preparation technique strongly affects some $^{4}$He wetting properties as has been seen in contact angle measurements of $^{4}$He on Cs surfaces. Of particular interest are Li surfaces which at low temperatures are predicted (1) to be superfluid with less than monolayer total $^{4}$He coverage. We have grown Li films on using 532 nm light from an Nd-YAG laser on to room temperature quartz crystal microbalances (QCM). We will present measurements of film growth rate as a function of the laser fluence. Preliminary $^{4}$He isotherm measurements on Li films laser ablated onto 4K QCMs will be compared with adsorption isotherms on the heavier alkali metal surfaces. $\linebreak$ $\linebreak$ (1) Massimo Boninsegni and Milton W. Cole, J. Low Temp. Phys. 113, 393 (1998).