Interaction between Two-Dimensional White-Light Photovoltaic Dark Spatial Solitons

Using fully incoherent white light emitted from an incandescent bulb (a line source) and amplitude mask, we study experimentally the interaction between two 2D white-light photovoltaic dark spatial solitons with three different separations (40μm, 50μm and 60μm) and arrangement directions (parallel to, perpendicular to and tilted at 45° with respect to the crystalline c axis) propagating in parallel in close proximity in self-defocusing LiNbO₃:Fe crystal. Experimental results reveal that a 2D white-light dark soliton pair only experiences attractive forces when their mutual separation is sufficiently small (<60μm), and the degree of the attraction depends on their mutual separation and their arrangement direction. When the separation is larger than 60μm, the interaction is not evident.