Abstract

The advantage of using nanosecond pulses to generate the large thermal nonlinearity that arises from the absorption of laser beams in liquid media is that one can avoid the problems of the spatial nonlocality of the nonlinearity owing to the convection currents and diffusion that are associated with cw beams. By using 10 ns laser pulses that passed through a cross wire placed behind an absorbing liquid, we found evidence of the generation of stable spatial dark solitons from the near-field and far-field patterns generated by low-intensity and high-intensity beams. We also observed evidence of the formation of spatial dark solitons when the cross wire was replaced by a phase plate. We plan to measure the transverse velocity, modulation depth, and other constants of motion and compare them with the theoretically predicted values. The spatial dark solitons are particular solutions of the nonlinear Schrodinger equation, which describes wave propagation in a medium with a large negative nonlinearity. Another consequence of this equation was recently pointed out by Agrawal,¹ who showed that for two copropagating but not completely overlapping beams, cross-phase modulation can take place without energy exchange. We have observed large two-beam coupling in thermal media and will present the results of our investigation of the effect predicted by Agrawal.

© 1990 Optical Society of America