We demonstrate fourth-harmonic generation from a GaAs(001) surface by using femtosecond pulses well below damage threshold. Our data reveal a strong fourfold anisotropic surface-specific polarization that is not present in second-harmonic generation and is nearly as strong as the bulk polarization.
© 1997 Optical Society of America
Y.-S. Lee, M. H. Anderson, and M. C. Downer, "Fourth-harmonic generation at a crystalline GaAs(001) surface," Opt. Lett. 22, 973-975 (1997)