Negative-frequency dispersive wave generation in quadratic media

TL;DR

This paper demonstrates that negative-frequency dispersive wave generation, previously observed in Kerr media, can also occur in quadratic media through second-harmonic generation, independent of the nonlinear mechanism or pulse dynamics.

Contribution

It introduces a unified formula for predicting dispersive wave frequencies in quadratic media, extending the understanding of negative-frequency wave phenomena beyond Kerr media.

Findings

Negative-frequency dispersive waves observed in quadratic media.

Unified formula accurately predicts emission frequencies.

Phenomenon occurs regardless of pulse soliton-like features or wave-breaking.

Abstract

We show that the extremely blue-shifted dispersive wave emitted in Kerr media owing to the coupling with the negative-frequency branch [Phys. Rev. Lett. {\bf 108}, 253901 (2012)] can be observed in quadratic media via second-harmonic generation. Not only such phenomenon is thus independent on the specific nonlinear mechanism, but it is shown to occur regardless of the fact that the process is pumped by a pulse which exhibits soliton-like features or, viceversa, undergoes wave-breaking. A simple unified formula gives the frequencies of the emitted dispersive waves in both cases.