Fresnel diffraction of spin waves

Spin waves, which have long been investigated for their potential in microwave electronics, found a renewed interest in the emerging field of magnonics, with promising functionalities for computation applications. In this context, several concepts of optics are applied to spin-waves, which includes recent works on the generation of spin-wave beams in continuous thin films from constricted coplanar waveguides (CPW) [1,2]. In this work, we explore experimentally the nature of the emission for the isotropic magnetostatic forward volume wave mode via spin-wave spectroscopy [3]. We found that the spin wave propagation remains focused in a beam of width comparable to that of the constriction, and that the spin-wave amplitude displays oscillations in the direction transverse to the propagation. Both of these features are understood in the framework of the Fresnel theory of near-field diffraction. These findings are of particular importance for future exploration of spin-wave interferometry.