Linear and nonlinear diffraction of dipolar spin waves in yttrium iron garnet films observed by space- and time-resolved Brillouin light scattering

An advanced space- and time-resolved Brillouin light-scattering technique i s used to study diffraction of two-dimensional beams and pulses of dipolar spin waves excited by strip-line antennas in tangentially magnetized garnet films. The technique is an effective tool for investigation of two-dimensi onal spin-wave propagation with high spatial and temporal resolution. Linea r effects, such as the unidirectional excitation of magnetostatic surface w aves and the propagation of backward volume magnetostatic waves (BVMSW) in two preferential directions due to the noncollinearity of their phase and g roup velocities, are investigated in detail. In the nonlinear regime, stati onary and nonstationary self-focusing effects are studied. It is shown that nonlinear evolution of a stationary BVMSW beam, having a finite transverse aperture, lends to self-focusing of the beam at one spatial point. Evoluti on of a finite-duration (nonstationary) BVMSW pulse leads to space-time sel f-focusing and formation of a strongly localized two-dimensional wave packe t (spin-wave bullet). Theoretical modeling of the self-focusing and diffrac tion processes by using a variational approach and direct numerical integra tion of the two-dimensional nonlinear Schrodinger equation provides a good qualitative description of the observed phenomena.