Optical spin-wave detection beyond the diffraction limit

Spin waves are proposed as information carriers for next-generation computing devices because of their low power consumption. Moreover, wave-like nature allows novel paradigms. Conventional methods to detect spin based either on electrical induction, limiting the downscaling and efficiency complicating eventual implementation, or light scattering, where minimum detectable spin-wave wavelength is set by laser. In this Article we demonstrate magneto-optical detection beyond diffraction limit using a metallic grating that selectively absorbs laser light. Specifically, propagating with 700 nm diffraction-limited spot size 10 $\mu$m in 20 thick Py strips. Additionally, show selective wave, providing wavevector-selective detection. This should open up new avenues towards integration burgeoning fields photonics magnonics, aid optical short-wavelength exchange regime fundamental research.