RESUMO
Ultrafast laser-induced magnetization dynamics in ferromagnetic thin films were measured using a femtosecond Ti:sapphire laser in a pump-probe magneto-optic Kerr effect setup. The effect of plasmon resonance on the transient magnetization was investigated by drop-coating the ferromagnetic films with dimensionally-tuned gold nanorods supporting longitudinal surface plasmon resonance near the central wavelength of the pump laser. With ~4% nanorod areal coverage, we observe a >50% increase in demagnetization signal in nanorod-coated samples at pump fluences on the order of 0.1 mJ/cm(2) due to surface plasmon-mediated localized electric-field enhancement, an effect which becomes more significant at higher laser fluences. We were able to qualitatively reproduce the experimental observations using finite-difference time-domain simulations and mean-field theory. This dramatic enhancement of ultrafast laser-induced demagnetization points to possible applications of nanorod-coated thin films in heat-assisted magnetic recording.
RESUMO
We present the theory and design of a Mach-Zehnder interferometer with orthogonally polarized arms that passively, noninvasively, optically amplifies polarization rotation in one arm of the interferometer. Theoretical analysis of the electric fields in the two arms is used to compare the significance of device optimizations. Design of the beam alignment, beam recombination, noise isolation, and active stabilization to enable reliable measurements are thoroughly discussed. Finally, we review a comparison between the interferometer with an optical gain factor of approximately 4.5 and the optical bridge (OB) technique for polarization rotation detection that shows the interferometer offers better performance than the OB.