5,331 research outputs found
Third-harmonic generation in photonic topological metasurfaces
We study nonlinear effects in two-dimensional photonic metasurfaces
supporting topologically-protected helical edge states at the nanoscale. We
observe strong third-harmonic generation mediated by optical nonlinearities
boosted by multipolar Mie resonances of silicon nanoparticles. Variation of the
pump-beam wavelength enables independent high-contrast imaging of either bulk
modes or spin-momentum-locked edge states. We demonstrate topology-driven
tunable localization of the generated harmonic fields and map the
pseudospin-dependent unidirectional waveguiding of the edge states bypassing
sharp corners. Our observations establish dielectric metasurfaces as a
promising platform for the robust generation and transport of photons in
topological photonic nanostructures.Comment: 5 pages, 5 figure
Optical third harmonic generation in black phosphorus
We present a calculation of Third Harmonic Generation (THG) for two-band
systems using the length gauge that avoids unphysical divergences otherwise
present in the evaluation of the third order current density response. The
calculation is applied to bulk and monolayer black Phosphorus (bP) using a
non-orthogonal tight-binding model. Results show that the low energy response
is dominated by mixed inter-intraband processes and estimates of the magnitude
of THG susceptibility are comparable to recent experimental reports for bulk bP
samples.Comment: 9 pages, 5 figure
Angular Dependences of Third Harmonic Generation from Microdroplets
We present experimental and theoretical results for the angular dependence of
third harmonic generation (THG) of water droplets in the micrometer range (size
parameter ). The THG signal in - and -polarization obtained
with ultrashort laser pulses is compared with a recently developed nonlinear
extension of classical Mie theory including multipoles of order .
Both theory and experiment yield over a wide range of size parameters
remarkably stable intensity maxima close to the forward and backward direction
at ``magic angles''. In contrast to linear Mie scattering, both are of
comparable intensity.Comment: 4 pages, RevTeX, 3 figures available on request from
[email protected], submitted to PR
Cascaded third harmonic generation in lithium niobate nanowaveguides
We predict highly efficient third harmonic generation through simultaneous phase-matching of second-harmonic generation and sum-frequency generation in lithium niobate nanowaveguides, enabled due to strong modal dispersion. We demonstrate that the waveguide size which corresponds to phase-matching is also optimal for highest mode confinement and therefore for strongly enhanced conversion efficiency.We acknowledge the support by the Australian Research
Council, the Australian Academy of Science, Australian National
Computational Infrastructure, and German Research
Foundation, Grant No. NanoGuide, PE 1524/5-1
Symmetry selective third harmonic generation from plasmonic metacrystals
Nonlinear processes are often governed by selection rules imposed by the
symmetries of the molecular configurations. The most well-known examples
include the role of mirror symmetry breaking for the generation of even
harmonics, and the selection rule related to the rotation symmetry in harmonic
generation for fundamental beams with circular polarizations. While the role of
mirror symmetry breaking in second harmonic generation has been extensively
studied in plasmonic systems, the investigation on selection rules pertaining
to circular polarization states of harmonic generation has been limited to
crystals, i.e. symmetries at the atomic level. Here we demonstrate the
rotational symmetry dependent third harmonic generation from nonlinear
plasmonic metacrystals. We show that the selection rule can be imposed by the
rotational symmetry of meta-crystals embedded into an isotropic organic
nonlinear thin film. The results presented here may open new avenues for
designing symmetry-dependent nonlinear optical responses with tailored
plasmonic nanostructures.Comment: 13 pages, 3 figure
Dynamical mean field theory of optical third harmonic generation
We formulate the third harmonic generation (THG) within the dynamical mean
field theory (DMFT) approximation of the Hubbard model. In the limit of large
dimensions, where DMFT becomes exact, the vertex corrections to current
vertices are identically zero, and hence the calculation of the THG spectrum
reduces to a time-ordered convolution, followd by appropriate analytic
continuuation. We present the typical THG spectrum of the Hubbard model
obtained by this method. Within our DMFT calculation, we observe a nontrivial
approximate {\em scaling} function describing the THG spectra in all Mott
insulators, independent of the gap magnitude.Comment: 4 eps figure
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