Collision kernels from velocity-selective optical pumping with magnetic depolarization

We experimentally demonstrate how magnetic depolarization of velocity-selective optical pumping can be used to single out the collisional cusp kernel best describing spinand velocity-relaxing collisions between potassium atoms and low-pressure helium. The range of pressures and transverse fields used simulate the optical pumping regime pertinent to sodium guidestars employed in adaptive optics. We measure the precession of spin-velocity modes under the application of transverse magnetic fields, simulating the natural configuration of mesospheric sodium optical pumping in the geomagnetic field. We also provide a full theoretical account of the experimental data using the recently developed cusp kernels, which realistically quantify velocity damping collisions in this optical pumping regime. A single cusp kernel with a sharpness s = 13 ± 2 provides a global fit to the K-He data.