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@@ -215,11 +215,11 @@ baranov2016nonlinear, baranov2016tuning} and
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metasurfaces~\cite{iyer2015reconfigurable, shcherbakov2015ultrafast,
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yang2015nonlinear}.
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-In all this works on all-dielectric nonlinear nanostructures, the
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+In these works on all-dielectric nonlinear nanostructures, the
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building blocks (nanoparticles) were considered as objects with
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dielectric permittivity homogeneously distributed over
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-nanoparticle. Therefore, in order to manipulate by propagation angle
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-of transmitted light it is necessary to use complicated nanostructures
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+nanoparticle. Therefore, in order to manipulate the propagation angle
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+of the transmitted light it is necessary to use complicated nanostructures
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with reduced symmetry~\cite{albella2015switchable, baranov2016tuning,
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shibanuma2016unidirectional}.
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@@ -236,16 +236,16 @@ In this Letter, we show that ultra-short laser-based EHP photo-excitation in
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a spherical semiconductor (e.g., silicon) nanoparticle leads to a strongly
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inhomogeneous carrier distribution. To reveal and study this effect, we
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perform a full-wave numerical simulation of the intense
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-femtosecond ($f\!s$) laser pulse interaction with a silicon
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+femtosecond ($\,f\!s$) laser pulse interaction with a silicon
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nanoparticle supporting Mie resonances and two-photon free carrier generation. In particular, we couple finite-difference time-domain (FDTD)
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method used to solve Maxwell equations with kinetic equations describing
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nonlinear EHP generation. Three-dimensional transient variation of the material dielectric permittivity is calculated for nanoparticles of several sizes. The obtained results propose a novel strategy to create
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complicated non-symmetrical nanostructures by using photo-excited
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-single spherical silicon nanoparticles. Moreover, we show that dense EHP can
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+single spherical silicon nanoparticles. Moreover, we show that a dense EHP can
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be generated at deeply subwavelength scale
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-($\approx$$\lambda$$^3$/100) supporting formation of small metalized
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-parts inside the nanoparticle, which transforms all-dielectric
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-nanoparticle to a hybrid one that extends functionality of the ultrafast
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+($\approx$$\lambda$$^3$/100) supporting the formation of small metalized
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+parts inside the nanoparticle. In fact, such effects transform an all-dielectric
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+nanoparticle to a hybrid one strongly extending functionality of the ultrafast
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optical nanoantennas.
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@@ -272,7 +272,7 @@ optical nanoantennas.
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\section{Modeling details}
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-We focus out attention on silicon because this material is promising
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+We focus attention on silicon because this material is promising
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for the implementation of numerous nonlinear photonic devices. This advantage is based on a broad
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range of optical nonlinearities, strong two-photon absorption, as well as a possibility of the photo-induced EHP
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excitation~\cite{leuthold2010nonlinear}. Furthermore, silicon
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@@ -309,7 +309,7 @@ where $\theta$ is the temporal pulse width at the half maximum (FWHM), $t_0$ is
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\subsection{Material ionization}
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-To account for the material ionization that is induced by a sufficiently intense laser field inside the particle, we couple Maxwell's equations with the kinetic equation for the electron-hole plasma as follows
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+To account for the material ionization that is induced by a sufficiently intense laser field inside the particle, we couple Maxwell's equations with the kinetic equation for the electron-hole plasma as described below.
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% \begin{figure*}[ht!]
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% \centering
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% \includegraphics[width=120mm]{fig2.png}
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@@ -331,10 +331,22 @@ where $I=\frac{n}{2}\sqrt{\frac{\epsilon_0}{\mu_0}}\left|\vec{E}\right|^2$ is th
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\begin{tabular*}{0.76\textwidth}{ c@{\extracolsep{\fill}} c@{\extracolsep{\fill}} c@{\extracolsep{\fill}} c@{\extracolsep{\fill}} c}
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$-80\:f\!s$&$-60\:f\!s$&$-30\:f\!s$&$ -20\:f\!s$&$ -10\:f\!s$\\
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\end{tabular*}
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+{\setlength\topsep{-1pt}
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+\begin{flushleft}
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+$R=75$~nm
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+\end{flushleft}}
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\includegraphics[width=0.9\textwidth]{2nm_75}
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+{\setlength\topsep{-1pt}
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+\begin{flushleft}
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+$R=100$~nm
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+\end{flushleft}}
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\includegraphics[width=0.9\textwidth]{2nm_100}
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+{\setlength\topsep{-1pt}
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+\begin{flushleft}
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+$R=115$~nm
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+\end{flushleft}}
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\includegraphics[width=0.9\textwidth]{2nm_115}
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-\caption{\label{plasma-105nm} Evolution of lectron density $n_e$ (using $10^{\,20} \ {\rm cm}^{-3}$ units) for (a--e)~$R=75$, (f--j)~$R=100$~nm, and (k--o)~$R=115$~nm. Gaussian pulse duration $80\:f\!s$, snapshot are taken before the pulse maxima, the corresponding time-shifts are shown in the top of each column.}
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+\caption{\label{plasma-105nm} Evolution of electron density $n_e$ (using $10^{\,20} \ {\rm cm}^{-3}$ units) for (a$\,$--$\,$e)~$R=75$~nm, (f$\,$--$\,$j$\,$)~$R=100$~nm, and ($\,$k$\,$--$\,$o)~$R=115$~nm. Gaussian pulse duration $80\:f\!s$, snapshots are taken before the pulse maxima, the corresponding time-shifts are shown in the top of each column. Laser irradiation fluences are (a-e) $0.12$ J/cm$^2$, (f-o) $0.16$ J/cm$^2$.}
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\end{figure*}
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The changes of the real and imaginary parts of the permittivity associated with the time-dependent free carrier response \cite{Sokolowski2000} can be derived from equations (\ref{Maxwell}, \ref{Drude}) and are written as follows
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@@ -384,10 +396,7 @@ electron densities $n_e$. We stress here that such regime
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could be still safe for nanoparticle due to the very small volume where such high
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EHP density is formed.
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-TODO: need to discuss this -
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-Of cause, this plasma is expected to diffuse after the considered time and turn to the homogeneously distributed one over the nanoparticle volume with a smaller density. Part of the electrons can also be ejected/injected into the surrounding medium, the process known to depend on the Shottky barrier at the particle border.
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-
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-\subsection{Effects of nanoparticle size/scattering efficiency factor
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+\subsection{Effects of nanoparticle size and scattering efficiency factor
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on scattering directions}
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% \begin{figure}[ht] \centering
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