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@@ -467,7 +467,11 @@ license.
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\caption{\label{time-evolution} Temporal EHP (a, c, e) and asymmetry factor
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$G_{N_e}$ (b, d, f) evolution for different Si nanoparticle radii of
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(a, b) $R = 75$~nm, (c, d) $R = 100$~nm, and (e, f) $R = 115$~nm. Pulse
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- duration $50$~\textit{fs} (FWHM). Wavelength $800$~nm in air. (b,
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+ duration $50$~\textit{fs} (FWHM). \red{\textbf{TODO:} on the plot
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+ it looks more like 75 fs for FWHM!!! Anton? \textbf{TODO2:} in
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+ text period of 800nm light is 2.6 fs, on the plot it is for sure
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+ < 2 fs. Anton???}
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+ Wavelength $800$~nm in air. (b,
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d, f) Different stages of EHP evolution shown in Fig.~\ref{plasma-grid}
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are indicated. The temporal evolution of Gaussian beam intensity is
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also shown. Peak laser fluence is fixed to be $0.125$~J/cm$^2$.}
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@@ -506,7 +510,7 @@ license.
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determined in a similar way by using volume integrals of squared
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intensity to predict EHP asymmetry due to two-photon absorption.
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Fig.~\ref{mie-fdtd}(b) shows $G$ factors as a function of the NP
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- size. For the NPs of sizes below the first magnetic dipole resonance,
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+ size. For the NPs of sizes below the first MD resonance,
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the intensity is enhanced in the front side as in
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Fig.~\ref{mie-fdtd}(c) and $G_I > 0$. The behavior changes near the
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size resonance value, corresponding to $R \approx 105$~nm. In
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@@ -538,7 +542,12 @@ license.
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EHP densities and the asymmetry factor $G_{N_e}$. It reveals the EHP
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evolution stages during pulse duration. Typical change of the
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permittivity corresponding to each stage is shown in
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- Fig.~\ref{plasma-grid}.
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+ Fig.~\ref{plasma-grid}. For better visual representation of time
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+ scale of the whole incident pulse and its single optical cycle we put a
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+ squared electric field profile on all plots at
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+ Fig.~\ref{time-evolution} in gray color as a backgroud image (note
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+ linear time scale on the left column and logarithmic scale on the
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+ right one).
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To describe all the stages of light non-linear interaction with Si
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NP, we present the calculation results obtained by using Maxwell's
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@@ -546,30 +555,29 @@ license.
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radii for resonant and non-resonant conditions. In this case, the
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geometry of the EHP distribution can strongly deviate from the
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intensity distribution given by Mie theory. Two main reasons cause
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- the deviation: (i) non-stationarity of the energy deposition and (ii)
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- nonlinear effects, taking place due to transient optical changes in
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- Si. The non-stationary intensity deposition results in different time
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- delays for exciting electric and magnetic resonances inside Si NP
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- because of different quality factors $Q$ of the resonances.
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-
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- In particular, magnetic dipole resonance (\textit{b1}) has
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- $Q \approx 8$, whereas electric one (\textit{a1}) has $Q \approx
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- 4$. The larger particle supporting magnetic quadrupole resonance
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- (\textit{b2}) demonstrates \textit{Q} $\approx 40$. As soon as the
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- electromagnetic wave period at $\lambda$~=~800~nm is 2.6~\textit{fs},
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- one needs about 10~\textit{fs} to pump the electric dipole,
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- 20~\textit{fs} for the magnetic dipole, and about 100~\textit{fs} for
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- the magnetic quadrupole. According to these considerations, after few
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- optical cycles taking place on a 10~\textit{fs} scale it results in
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- the excitation of the low-\textit{Q} electric dipole resonance
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- independently on the exact size of NPs. Moreover, during the first
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- optical cycle there is no multiple mode structure inside of NP, which
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- results into a very similar field distribution for all size of NP
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- under consideration. We address to this phenomena as
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- \textit{'Stage~1'}, as shown in Figs.~\ref{plasma-grid}(a,e,i).
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- and~\ref{plasma-grid}. The first stage at the first optical cycle
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- demonstrates the initial penetration of electromagnetic fild into the
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- NP.
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+ the deviation: (i) non-stationarity of interaction between
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+ electromagnetic pulse and NP (ii) nonlinear effects, taking place due
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+ to transient optical changes in Si. The non-stationary intensity
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+ deposition during \textit{fs} pulse results in different time delays
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+ for exciting electric and magnetic resonances inside Si NP because of
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+ different quality factors $Q$ of the resonances.
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+
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+ In particular, MD resonance (\textit{b1}) has $Q \approx 8$, whereas
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+ electric one (\textit{a1}) has $Q \approx 4$. The larger particle
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+ supporting MQ resonance (\textit{b2}) demonstrates $ Q \approx
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+ 40$. As soon as the electromagnetic wave period at $\lambda = 800$~nm
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+ is 2.6~\textit{fs}, one needs about 10~\textit{fs} to pump the ED,
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+ 20~\textit{fs} for the MD, and about 100~\textit{fs} for the MQ.
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+ According to these considerations, after few optical cycles taking
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+ place on a 10~\textit{fs} scale it results in the excitation of the
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+ low-\textit{Q} ED resonance, which dominates MD and МQ independently
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+ on the exact size of NPs. Moreover, during the first optical cycle
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+ there is no multiple mode structure inside of NP, which results into
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+ a very similar field distribution for all size of NP under
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+ consideration as shown in Figs.~\ref{plasma-grid}(a,e,i) . We address
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+ to this phenomena as \textit{'Stage~1'}. This stage demonstrates the
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+ initial penetration of electromagnetic field into the NP during the
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+ first optical cycle.
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\textit{'Stage~2'} corresponds to further electric field oscillations
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($t \approx 2\div15$) leading to the unstationery EHP evolution
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@@ -584,19 +592,19 @@ license.
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Mie-based intensity distribution at the \textit{'Stage~3'} (see
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Fig.~\ref{time-evolution}). The EHP density is still relatively small to affect
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the EHP evolution or for diffusion, but is already high enough to
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- change the local optical properties. Below the magnetic dipole
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+ change the local optical properties. Below the MD
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resonance $R \approx 100$~nm, the EHP is mostly localized in the
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front side of the NP as shown in Fig.~\ref{plasma-grid}(c). The highest
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stationary asymmetry factor $G_{N_e} \approx 0.5\div0.6$ is achieved
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- in this case. At the magnetic dipole resonance conditions, the EHP
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+ in this case. At the MD resonance conditions, the EHP
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distribution has a toroidal shape and is much closer to the
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- homogeneous distribution. In contrast, above the magnetic dipole
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+ homogeneous distribution. In contrast, above the MD
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resonant size for $R = 115$~nm, and the $G_{N_e} < 0$ due to the fact
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that EHP is dominantly localized in the back side of the NP.
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For the higher excitation conditions, the optical properties of
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silicon change significantly according to the equations
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- (\ref{Index}). As a result, the non-resonant electric dipole
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+ (\ref{Index}). As a result, the non-resonant ED
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contributes to the forward shifting of EHP density
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maximum. Therefore, EHP is localized in the front part of the NP,
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influencing the asymmetry factor $G_{N_e}$ in
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@@ -619,7 +627,7 @@ license.
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It is worth noting that it is possible to achieve a formation of
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deeply subwavelength EHP regions due to high field localization. The
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smallest EHP localization and the larger asymmetry factor are
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- achieved below the magnetic dipole resonant conditions for $R < 100$~nm.
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+ achieved below the MD resonant conditions for $R < 100$~nm.
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Thus, the EHP distribution in Fig.~\ref{plasma-grid}(c) is optimal for
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symmetry breaking in Si NP, as it results in the larger asymmetry
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factor $G_{N_e}$ and higher electron densities $N_e$. We stress here
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