Radiation of caustic beams from a collapsing bullet

TL;DR

This paper investigates the radiation of caustic beams from a collapsing spin-wave bullet in a ferrimagnetic medium, combining theoretical predictions with experimental validation to reveal the formation of caustic beams at specific angles.

Contribution

It provides the first experimental observation of caustic beams emitted by a collapsing wave packet in a magnetic medium, confirming theoretical predictions about their angles and nature.

Findings

Collapse of a spin-wave bullet emits narrow caustic beams.

Beams are at specific angles, identified as spin-wave caustic angles.

Experimental results agree with theoretical calculations.

Abstract

Collapse of an intense (2+1)-dimensional wave packet in a medium with cubic nonlinearity and a two-dimensional dispersion of an order higher than parabolic is studied both theoretically and experimentally. The carrier waves are microwave backward volume spin waves which propagate in a stripe made from a thin ferrimagnetic film and the packet is a spin-wave bullet. We show that before being self-destroyed the bullet irradiates untrapped dispersive waves, which is in agreement with a previous theoretical prediction. Since, in addition, the ferromagnetic medium is characterized by an induced uniaxial anisotropy, this radiation takes the form of narrow beams of continuous waves at very specific angles to its propagation direction. Based on our theoretical calculations we find that these beams are caustic beams and the angles are the characteristic spin-wave caustic angles modified by the motion of the source.