212 research outputs found
Interferometry of hyper-Rayleigh scattering by inhomogeneous thin films
The use of specific symmetry properties of the optical second-harmonic
generation (the s,s-exclusion rule) has allowed us to observe high-contrast
hyper-Rayleigh interference patterns in a completely diffuse light - an effect
having no analog in case of linear (Rayleigh) scattering.Comment: 8 pages, 3 figure
DC-electric-field-induced and low-frequency electromodulation second-harmonic generation spectroscopy of Si(001)-SiO interfaces
The mechanism of DC-Electric-Field-Induced Second-Harmonic (EFISH) generation
at weakly nonlinear buried Si(001)-SiO interfaces is studied experimentally
in planar Si(001)-SiO-Cr MOS structures by optical second-harmonic
generation (SHG) spectroscopy with a tunable Ti:sapphire femtosecond laser. The
spectral dependence of the EFISH contribution near the direct two-photon
transition of silicon is extracted. A systematic phenomenological model of the
EFISH phenomenon, including a detailed description of the space charge region
(SCR) at the semiconductor-dielectric interface in accumulation, depletion, and
inversion regimes, has been developed. The influence of surface quantization
effects, interface states, charge traps in the oxide layer, doping
concentration and oxide thickness on nonlocal screening of the DC-electric
field and on breaking of inversion symmetry in the SCR is considered. The model
describes EFISH generation in the SCR using a Green function formalism which
takes into account all retardation and absorption effects of the fundamental
and second harmonic (SH) waves, optical interference between field-dependent
and field-independent contributions to the SH field and multiple reflection
interference in the SiO layer. Good agreement between the phenomenological
model and our recent and new EFISH spectroscopic results is demonstrated.
Finally, low-frequency electromodulated EFISH is demonstrated as a useful
differential spectroscopic technique for studies of the Si-SiO interface in
silicon-based MOS structures.Comment: 31 pages, 14 figures, 1 table, figures are also available at
http://kali.ilc.msu.su/articles/50/efish.ht
Optical second harmonic generation probe of two-dimensional ferroelectricity
Optical second harmonic generation (SHG) is used as a noninvasive probe of
two-dimensional (2D) ferroelectricity in Langmuir-Blodgett (LB) films of
copolymer vinylidene fluoride with trifluorethylene. The surface 2D
ferroelectric-paraelectric phase transition in the topmost layer of LB films
and a thickness independent (almost 2D) transition in the bulk of these films
are observed in temperature studies of SHG.Comment: 9 pages, 2 figures, Optics Letters, in prin
Optical second harmonic generation near a black hole horizon as possible source of experimental information on quantum gravitational effects
Optical second harmonic generation near a black hole horizon is suggested as
a source of experimental information on quantum gravitational effects. While
absent in the framework of general relativity, second harmonic generation
appears in the toy models of sonic and electromagnetic black holes, where
spatial dispersion at high frequencies for waves boosted towards the horizon is
introduced. Localization effects in the light scattering from random
fluctuations of matter fields and space-time metric near the black hole horizon
produce a pronounced peak in the angular distribution of second harmonics of
light in the direction normal to the horizon. Such second harmonic light has
the best chances to escape the vicinity of the black hole. This phenomenon is
similar to the well-known strong enhancement of diffuse second harmonic
emission from a randomly rough metal surface in the direction normal to the
surface.Comment: 4 pages, 1 figur
Ultrafast transport of laser-excited spin polarized carriers in Au/Fe/MgO(001)
A time domain approach to probe hot carrier-induced spin dynamics is
demonstrated. The experiments are performed in epitaxial Au/Fe/MgO(001), where
spin-polarized hot carriers are excited in the Fe layer by 35 fs laser pulses.
They propagate to the Au surface where the transient spin polarization is
detected by magneto-induced second harmonic generation. Different energies of
majority and minority hot carriers excited in the exchange-split Fe band
structure lead to their spindependent lifetimes in Au. Accordingly, two
spin-polarized current contributions which propagate superdiffusively at
different velocities result in a spin current pulse of about 100 fs duration.Comment: 5 pages, 4 figure
Surface-enhanced optical third-harmonic generation in Ag island films
Surface-enhanced optical third-harmonic generation (THG) is observed in
silver island films. The THG intensity from Ag nanoparticles is enhanced by
more than two orders of magnitude with respect to the THG intensity from a
smooth and homogeneous silver surface. This enhancement is attributed to local
plasmon excitation and resonance of the local field at the third-harmonic
wavelength. The diffuse and depolarized component of the enhanced THG is
associated with the third-order hyper-Rayleigh scattering in a 2-D random array
of silver nanoparticles.Comment: 4 pages, 2 figure
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