Optical spatial solitons and modulation instabilities in transparent entangled polymer solutions.

Fully transparent nondilute polydiene solutions exhibit optical nonlinearities when irradiated by a low-power cw laser in the visible. The formation of optical spatial solitons is imaged through phase contrast microscopy. Both (2+1)D and (1+1)D modulational instabilities are evidenced as 2D and 1D arrays of linear filaments formed by beam defocusing or by using a cylindrical lens. The origin of the nonlinearity remains elusive.