Spatial transformation of Laguerre-Gaussian laser modes

A method is described to spatially transform the annular profile of an arbitrary high-order Laguerre-Gaussian (LG) laser mode into an ultranarrow annulus using a combination of an axicon and a lens. The method is shown to conserve the azimuthal phase variation of the illuminating LG mode. The thin annular (hollow) light beam generated possesses orbital angular momentum and is suitable for experimental studies with cold atoms.