Nonlocal Damping of Helicon Waves

The nonlocal damping of helicon waves propagating in the simple metals is discussed. An approximate dispersion relation is presented which includes the effects of both normal collision damping and nonlocal damping. Two types of experiments designed to measure the damping in sodium and potassium are described. The first type involves measurements of the standing-wave resonances in thin-plate sodium samples. This technique is useful in the regime $\mathrm{ql}<\mathrm{}5\mathrm{}$, where $q$ is the helicon wave vector and $l$ is the carrier mean free path. The second type involves transmission experiments using both sodium and potassium. These experiments span the range $4\lesssim \mathrm{ql}\lesssim 30$. The experimental results are in close agreement with the theoretical predictions based on the free-electron model.