Femtosecond laser pulse driven caustic spin wave beams

TL;DR

This paper demonstrates control over the directionality of spin waves using femtosecond laser pulses, enabling tunable caustic patterns and propagation angles for potential magnonic device applications.

Contribution

It introduces an all-optical method to generate and control spin wave caustic patterns and directions via magnetic field detuning and resonance tuning.

Findings

Caustic spin-wave patterns at 70° angles observed

Propagation pattern switches with magnetic field detuning

Field-controlled spin wave directionality achieved

Abstract

Controlling the directionality of spin waves is a key ingredient in wave-based computing methods such as magnonics. In this paper, we demonstrate this particular aspect by using an all-optical point-like source of continuous spin waves based on frequency comb rapid demagnetization. The emitted spin waves contain a range of k-vectors and by detuning the applied magnetic field slightly off the ferromagnetic resonance (FMR), we observe X-shaped caustic spin-wave patterns at $70^{\circ}$ propagation angles as predicted by theory. When the harmonic of the light source approaches theFMR, the caustic pattern gives way to uniaxial spin-wave propagation perpendicular to the in-plane component of the applied field. This field-controlled propagation pattern and directionality of optically emitted short-wavelength spin waves provide additional degrees of freedom when designing magnonic devices.