Observation of all-optical bump-on-tail instability

TL;DR

This paper demonstrates an all-optical bump-on-tail instability through nonlinear interactions of partially-coherent beams, revealing regimes of weak and strong turbulence with spectral energy redistribution.

Contribution

It introduces the first observation of all-optical bump-on-tail instability and characterizes its regimes using holographic reconstruction of wave dynamics.

Findings

Observation of momentum transfer without intensity change in weak coupling

Detection of wave collapse and intensity modulations in strong coupling

Universal behavior applicable to various wave-kinetic systems

Abstract

We demonstrate an all-optical bump-on-tail instability by considering the nonlinear interaction of two partially-coherent spatial beams. For weak wave coupling, we observe momentum transfer with no variation in intensity. For strong wave coupling, modulations appear in intensity and evidence appears for wave (Langmuir) collapse at large scales. Borrowing plasma language, these limits represent regimes of weak and strong spatial optical turbulence. In both limits, the internal spectral energy redistribution is observed by recording and reconstructing a hologram of the evolving dynamics. The results are universal and can appear in any wave-kinetic system with short-wave/long-wave coupling.