Suppression of inhomogeneous broadening in rf spectroscopy of optically trapped atoms

We present a method for reducing the inhomogeneous frequency broadening in the hyperfine splitting of the ground state of optically trapped atoms. This reduction is achieved by the addition of a weak light field, spatially mode matched with the trapping field and whose frequency is tuned in between the two hyperfine levels. We experimentally demonstrate the new scheme with ${}^{85}\mathrm{Rb}$ atoms, and report a 50-fold narrowing of the rf spectrum.