We have observed time-varying spin relaxation of trapped cold atoms due to photon scattering in blue-detuned, crossed, hollow Laguerre-Gaussian beams. These beams are formed by imparting an azimuthal phase of $\ell \phi$ to a Gaussian beam, where $\ell$ is an integer, and have an intensity distribution that scales with $r^{2\ell }$ to the lowest order. For all degrees of anharmonicity, we observe a time-varying spin-relaxation rate due to energy-dependent photon scattering. For $\ell =8$, we directly measure temperature-dependent scattering rates and show that by removing the most energetic atoms from the trap, a more purely spin-polarized sample remains. The results agree well with Monte Carlo simulations, and we present a simple functional form for the spin-relaxation curves.

• Received 18 May 2011

DOI:https://doi.org/10.1103/PhysRevA.84.025402