Abstract

Very considerable interest has recently been shown in transverse optical instabilities and the formation of patterns occurring when a cw laser beam propagates through a nonlinear medium.^[1,2] We present here first observations of the control of such instability and near-field patterns through a direct, simple external parameter: a magnetic field applied transverse to the beam direction. In brief, the system (D₁ line of highly-buffered atomic sodium), and experimental conditions (circularly polarized laser radiation blue-detuned by a couple of homogeneous line widths), are chosen so that for zero magnetic field the beam propagates through the medium essentially without modification [Fig. 1 (a)]; whereas with increase of the magnetic field, transverse instability in the beam develops leading to patterns which can be initially nearcylindrically symmetric [see Fig. 1 (b) and (c)], but which ultimately break symmetry in a fully two-dimensional manner [Fig. 1 (d) and (e)].

© 1992 IQEC