  Magnonics is a prospective beyond CMOS technology which uses magnons, the
quanta of spin waves, for low-power information processing. Many magnonic
concepts and devices were recently demonstrated at macro- and microscale, and
now these concepts need to be realized at nanoscale. Brillouin light scattering
spectroscopy and microscopy (BLS) has become a standard technique for spin wave
visualization and characterization, and enabled many pioneering magnonic
experiments. However, due to its fundamental limit in maximum detectable magnon
momentum, the conventional BLS cannot be used to detect nanoscale spin waves.
Here we show that optically induced Mie resonances in dielectric nanoparticles
can be used to extend the range of accessible spin wave wavevectors beyond the
BLS fundamental limit. The method is universal and can be used in many magnonic
experiments dealing with thermally excited as well as coherently excited
high-momentum, short-wavelength spin waves. This discovery significantly
extends the usability and relevance of the BLS technique for nanoscale magnonic
research.
