arXiv subjects
Publications and source records attributed to Thomas Roger.
We theoretically analyze stimulated parametric down conversion as a means to produce dichroism based on the orbital angular momentum (OAM) of an incident signal field. The nonlinear interaction is shown to provide differential gain between signal states of differing OAM, the peak gain occurring at half the OAM of the pump field.
We report measurements that show extreme events in the statistics of resonant radiation emitted from spatiotemporal light bullets. We trace the origin of these extreme events back to instabilities leading to steep gradients in the temporal profile of the intense light bullet that occur during the initial collapse dynamics. Numerical simulations reproduce the extreme valued statistics of the resonant radiation which are found to be intrinsically linked to the simultaneous occurrence of both temporal and spatial self-focusing dynamics. Small fluctuations in both the input energy and in the spatial phase curvature explain the observed extreme behaviour.
We elucidate the consequences of a phase-matching theory that describes second-harmonic generation of two non-collinear incident light beams that carry orbital angular momentum (OAM). More specifically, the two incident beams generate a third that, depending on the incident OAM, may experience a significantly smaller conversion efficiency in comparison to that based on the conventional phase-matching theory. This is the case even for incident angles substantially less than those required for non-conservation of OAM in the nonlinear interaction. Experiments are performed under different conditions and are in excellent agreement with the theory. Our results have implications beyond the specific case studied here of second-harmonic generation, in particular for parametric down-conversion of photons.
We present a simple yet effective theory that predicts the existence of resonant radiation bands in the deep normal group velocity dispersion region of a medium, even in absence of a zero-group velocity dispersion point. This radiation is evident when the medium is pumped with high-energy ultrashort pulses, and it is driven by the interplay between the Kerr and the shock terms in the NLSE. Accurate experiments performed in bulk silica fully support the theoretical phase-matching condition found by our theory.