All-Optical Probe of Coherent Spin Waves

A novel, all-optical method to excite and detect spin waves in magnetic materials is presented. By exploiting the temperature dependence of the magnetic anisotropy, an ultrashort laser pulse is efficiently converted in a picosecond “anisotropy field” pulse that triggers a coherent precession of the magnetization. Recording the temporal evolution of the precessing spins by a time-delayed probe-pulse provides a quantitative method to study locally the magnetic anisotropy, as well as switching and damping phenomena in micromagnetic structures. Applications to nickel and permalloy ( ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$) films are discussed, particularly showing the possibility to explore standing spin waves in thin films.