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, their wave-like nature allows for novel computing paradigms. Conventional methods to detect propagating spin waves are based either on electrical induction, limiting the downscaling and efficiency complicating eventual implementation, or on light scattering, where the minimum detectable spin-wave wavelength is set by the wavelength of the laser unless near-field techniques are used. In this article, we demonstrate the magneto-optical detection of spin waves beyond the diffraction limit using a metallic grating that selectively absorbs laser light. Specifically, we demonstrate the detection of propagating spin waves with a wavelength of 700 nm in 20 nm thick Ni80Fe20 strips using a diffraction-limited laser spot with a diameter of 10 μ m. Additionally, we show that this grating is selective to the wavelength of the spin wave, providing phase-sensitive, wavevector-selective spin-wave detection in the time domain, thus providing a complementary approach to existing techniques such as Brillouin light scattering. This should open up new avenues toward the integration of the burgeoning fields of photonics and magnonics and aid in the optical detection of spin waves in the short-wavelength exchange regime for fundamental research.