7,964 research outputs found
Effect of the surface-stimulated mode on the kinetics of homogeneous crystal nucleation in droplets
A kinetic theory of homogeneous crystal nucleation in unary droplets is
presented taking into account that a crystal nucleus can form not only in the
volume-based mode (with all its facets within the droplet) but also in the
surface-stimulated one (with one of its facets at the droplet surface). The
previously developed thermodynamics of surface-stimulated crystal nucleation
rigorously showed that if at least one of the facets of the crystal is only
partially wettable by its melt, then it is thermodynamically more favorable for
the nucleus to form with that facet at the droplet surface rather than within
the droplet. So far, however, the kinetic aspects of this phenomenon had not
been studied at all. The theory proposed in the present paper advocates that
even in the surface-stimulated mode crystal nuclei initially emerge (as
sub-critical clusters) homogeneously in the sub-surface layer, not
"pseudo-heterogeneously" at the surface. A homogeneously emerged sub-critical
crystal can become a surface-stimulated nucleus due to density and structure
fluctuations. This effect contributes to the total rate of crystal nucleation
(as the volume-based mode does). An explicit expression for the total
per-particle rate of crystal nucleation is derived. Numerical evaluations for
water droplets suggest that the surface-stimulated mode can significantly
enhance the per-particle rate of crystal nucleation in droplets as large as 10
microns in radius. Possible experimental verification of the proposed theory is
discussed.Comment: 33 pages, 3 figure
Broadband light coupling to dielectric slot waveguides with tapered plasmonic nanoantennas
We propose and theoretically verify an efficient mechanism of broadband
coupling between incident light and on-chip dielectric slot waveguide by
employing a tapered plasmonic nanoantenna. Nanoantenna receives free space
radiation and couples it to a dielectric slot waveguide with the efficiency of
up to 20% in a broad spectral range, having a small footprint as compared with
the currently used narrowband dielectric grating couplers. We argue that the
frequency selective properties of such nanoantennas also allow for using them
as ultrasmall on-chip multiplexer/demultiplexer devices
Second-harmonic generation in subwavelength graphene waveguides
We suggest a novel approach for generating second-harmonic radiation in
subwavelength graphene waveguides. We demonstrate that quadratic phase matching
between the plasmonic guided modes of different symmetries can be achieved in a
planar double-layer geometry when conductivity of one of the layers becomes
spatially modulated. We predict theoretically that, owing to graphene nonlocal
conductivity, the second-order nonlinear processes can be actualized for
interacting plasmonic modes with an effective grating coupler to allow external
pumping of the structure and output of the radiation at the double frequency.Comment: 5 pages, 3 figure
Necklace-ring vector solitons
We introduce novel classes of optical vector solitons that consist of incoherently coupled self-trapped “necklace” beams carrying zero, integer, and even fractional angular momentum. Because of the stabilizing mutual attraction between the components, such stationary localized structures exhibit quasistable propagation for much larger distances than the corresponding scalar vortex solitons and expanding scalar necklace beams
- …