Gas of dark solitons generated by an optical shock

In this paper, we discuss the effect of a nonlinearity that outweighs diffraction in a defocusing nonlinear Kerr-like medium. In particular we show that a dark waveform, in this regime, focuses down until it develops a shock wave (singularity), which is then regularized by weak diffraction, showing the onset of fast oscillations characteristic of a so-called dispersive shock wave. The region filled with oscillations expand and behaving as a gas of non-interacting particles (multiple solitons). Here we report its experimental demonstration in a medium with thermal nonlinearity and the relative theory. Due to its generality, the shock and the post-shock dynamics survive the averaging effect of even strong nonlocality of the nonlinear response, thus being observable for a wide class of nonlinear materials such as liquid crystals, photorefractives, etc. Furthermore, in spite of its complexity, we show that the phenomenon is amenable to a completely analytical description in the local limit.