Excitation of magnon accumulation by laser clocking as a source of long-range spin waves in transparent magnetic films

TL;DR

This paper demonstrates a method to generate long-range, tunable spin waves in magnetic films using a train of femtosecond laser pulses, creating a coherent magnon accumulation that enhances propagation and control.

Contribution

It introduces a novel laser pulse train technique to produce a quasi-stationary magnon cloud, enabling longer, more controlled spin wave propagation in magnetic garnet films.

Findings

Achieved long-distance spin wave propagation up to 100 μm.

Enhanced spin wave amplitude through periodic laser excitation.

Generated narrow-spectrum, directional spin waves with tunable properties.

Abstract

Optical tools are of great promise for generation of spin waves due to the possibility to manipulate on ultrashort time scales and to provide local excitation. However, a single laser pulse can inject spin waves only with a broad frequency spectrum, resulting in a short propagation distance and low amplitude. Here we excite a magnetic garnet film by a train of fs-laser pulses with 1 GHz repetition rate so that pulse separation is smaller than decay time of the magnetic modes which allows to achieve collective photonic impact on magnetization. It establishes a quasi-stationary source of SWs, namely a coherent magnon accumulation ("magnon cloud"). This approach has several appealing features: (i) the source is tunable; (ii) the SW amplitude can be significantly enhanced; (iii) the spectrum of the generated SWs is quite narrow that provides longer propagation distance; (iv) the periodic pumping results in almost constant in time SW amplitude up to 100 um away from the source; and (v) the SW emission shows a pronounced directionality. These results expand the capabilities of ultrafast coherent optical control of magnetization and pave a way for applications in data processing, including the quantum regime. The quasi-stationary magnon accumulation might be also of interest for the problem of magnon Bose-Einstein condensate.