Self-trapping of incoherent white light

Abstract

Optical pulses-wave-packets-propagating in a linear medium have a natural tendency to broaden in time (dispersion) and space (diffraction). Such broadening can be eliminated in a nonlinear medium that modifies its refractive index in the presence of light in such a way that dispersion or diffraction effects are counteracted by light-induced lensing. This can allow short pulses to propagate without changing their shape, and the self- trapping of narrow optical beams whereby a beam of light induces a waveguide in the host medium and guides itself in this waveguide, thus propagating without diffraction. Self-trapped pulses in space and time have been investigated extensively in many physical systems and, as a consequence of their particle-like behavior, are known as 'solitons'. Previous studies of this phenomenon in various nonlinear media have involved coherent light, the one exception being our demonstration of self-trapping of an optical beam that exhibited partial spatial incoherence. Here we report the observation of self-trapping of a white-light beam from an incandescent source. Self- trapping occurs in both dimensions transverse to the beam when diffraction effects are balanced exactly by self-focusing in the host photorefractive medium. To the best of our knowledge, this is the first observation of self- trapping for any wave-packet that is both temporally and spatially incoherent.