Second-harmonic (SH) generation at the ferromagnetic Gd(0001) surface was investigated with 35-fs laser pulses and photon energies between 1.44 and 1.68 eV. In pump-probe mode the SH field was measured during the first 3 ps, and the time evolution, including contributions from coherent phonons and magnons, was analyzed. All data reveal strong changes with wavelength, which correlate with the SH magnetic contrast and can be well explained by the Gd(0001) exchange-split surface state. In SH interferometry an energy splitting of 13 meV was found that is attributed to a frequency modulation of the surface state by coherent phonons of approximately 3 THz.
© 2005 Optical Society of America
(160.3900) Materials : Metals
(190.7110) Nonlinear optics : Ultrafast nonlinear optics
(240.4350) Optics at surfaces : Nonlinear optics at surfaces
(300.6500) Spectroscopy : Spectroscopy, time-resolved
Alexey V. Melnikov, Ilie Radu, Uwe Bovensiepen, Kai Starke, Martin Wolf, and Eckart Matthias, "Spectral dependence of time-resolved coherent and incoherent second-harmonic response of ferromagnetic Gd(0001)," J. Opt. Soc. Am. B 22, 204-214 (2005)