Measurement of the Potassium 4PExcited State Diffusion Coefficient in Xenon Gas Using Degenerate Four-Wave Mixing

We present a method for measuring the diffusion coefficients for excited atoms in buffer gases that uses degenerate four-wave mixing. We show that, for low beam intensities and atomic densities, the relative angular response of the degenerate four-wave mixing signal is dependent on the excited state diffusion and decay rate only, and that it is independent of the ground state diffusion. We have experimentally measured the diffusion of potassium atoms in the $4P$ state in xenon and found that the diffusion coefficient $D$ at 155 °C and 760 torr is 0.084(4) c${\mathrm{m}}^2$ ${\mathrm{s}}^{–1}$.