title: Single-beam and enhanced two-beam second-harmonic generation from silicon nanocrystals by use of spatially inhomogeneous femtosecond pulses.
abstract: Optical second-harmonic generation (SHG) is used as a noninvasive probe of the interfaces of Si nanocrystals (NCs) embedded uniformly in an SiO2 matrix. Measurements of the generated SH mode verify that the second-harmonic polarization has a nonlocal dipole form proportional to (E x Delta inverted) E that depends on inhomogeneities in the incident field E, as proposed in recent models based on a locally noncentrosymmetric dipolar response averaged over the spherical NC interfaces. A two-beam SHG geometry is found to enhance this polarization greatly compared to single-beam SHG, yielding strong signals useful for scanning, spectroscopy, and real-time monitoring. This configuration provides a general strategy for enhancing the second-order nonlinear response of centrosymmetric samples, as demonstrated here for both Si nanocomposites and their glass substrates.
authors.affiliation: FOCUS Center, University of Texas at Austin, Department of Physics, Austin, Texas 78712-1081, USA.
authors.forename: P
authors.initials: P
authors.lastname: Figliozzi
authors.forename: L
authors.initials: L
authors.lastname: Sun
authors.forename: Y
authors.initials: Y
authors.lastname: Jiang
authors.forename: N
authors.initials: N
authors.lastname: Matlis
authors.forename: B
authors.initials: B
authors.lastname: Mattern
authors.forename: M C
authors.initials: MC
authors.lastname: Downer
authors.forename: S P
authors.initials: SP
authors.lastname: Withrow
authors.forename: C W
authors.initials: CW
authors.lastname: White
authors.forename: W L
authors.initials: WL
authors.lastname: Mochán
authors.forename: B S
authors.initials: BS
authors.lastname: Mendoza