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 spin and velocity relaxing collisions between potassium atoms and low pressure helium. The range of pressures and transverse fields used simulate the novel 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 novel optical pumping regime. A single cusp kernel with a sharpness $s=13\pm 2$ provides a global fit to the K-He data.