Selective Ultrafast Optical Excitation of High-Wave-Number Dynamics in a Magnetophotonic Nanostructure

Both the minimal size of optically switched magnetic bits and the wavelengths of optically excited spin waves in optomagnonic devices are fundamentally diffraction limited. Here, we propose and experimentally demonstrate a novel method to overcome these limitations by using a specially designed magnetophotonic waveguide structure. This structure enables the creation of a sign-changing profile of the inverse Faraday effect (IFE) induced in the magnetic film by the circularly polarized femtosecond laser pulse tuned to the resonance of the optical TE guided mode. The spatial period of the IFE profile is subdiffractive, which allows for the launch of narrow band exchange-dominated magnetostatic spin waves. As experimentally demonstrated, their wavelengths are around 300 nm, and they can potentially be reduced to 100 nm. This opens new horizons for optomagnetic applications, ranging from logic elements to data processing devices.