# 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.

## Key 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.

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Source: https://tomesphere.com/paper/1701.05109