Second‐harmonic spectroscopy of nano‐interfaces

Current address: School of Physics, Peking University, Beijing 100871, China
physica status solidi (c) 11/2005; 2(12):4067 - 4071. DOI: 10.1002/pssc.200562228

ABSTRACT Optical second-harmonic is shown to be a noninvasive, interface-sensitive probe of silicon nanocrystals. The TEM01 spatial mode of SHG radiation from a silicon nanocrystal composite indicates there is nonlocal dipolar (quadrupolar) polarization source which is proportional to the gradient of the incoming electric field. With two orthogonally polarized laser beams, we enhanced the SHG from nanocrystals by creating wavelength-scale, forward-radiating gradient in the second-harmonic polarization. The quantitative features of two-beam SHG were also studied with a fused silica slide. We demonstrate several techniques for isolating the nano-interface signal from the (bulk-quadrupolar) substrate signal in our samples. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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    ABSTRACT: Extending previous second-harmonic generation (SHG) single-wavelength studies [1] of Si nanocrystals (NCs) embedded in fused silica, we implement spectroscopic cross-polarized two-beam SHG (XP2-SHG) by employing an optical parametric amplifier as a source of widely tunable (1.6 ≤ Eph ≤ 2.4 eV) femtosecond pulses.Subsequent isolation of the SH signal produced by the NCs yields the oscillator strength and phase of their nonlinear response. We obtain a broad resonance between bulk Si E1 and E2 critical points. Possible explanations for the spectroscopic result are discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 05/2008; 5(8):2662 - 2666.

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