Most lasers have a round Gaussian beam profile, however it is also possible to make Laguerre-Gauss beams with a ‘donut’ -shaped cross-section. When you add two light sources with a narrow enough frequency (colour) width, then you can get regions of constructive and destructive interference, like in the classic Young’s double slit experiment. The same thing is true when you add two Laguerre-Gauss beams and you then get bright and dark fringes around a ring. By creating a slight difference in the frequency of the two Laguerre-Gauss beams it is possible to make the interference pattern rotate.
Using a different technique, if you wiggle (scan) a Gaussian beam around at high enough frequencies you can trace out complex patterns. This work is related to the Laguerre-Gauss superposition beams, however interferometric stability is no longer a requirement for reproducible patterns – the phase of the lattice is purely defined by the acousto-optic modulators’ radio frequency control.We intend to use these patterns in conjunction with our Bose-Einstein condensation experiments.
S. Franke-Arnold, J. Leach, M.J. Padgett, V.E. Lembessis, D. Ellinas, A.J. Wright, J.M. Girkin, P. Öhberg and A. S. Arnold, Optical ferris wheel for ultracold atoms, Opt. Express 15, 8619 (2007).
