Metal nanofilm in strong ultrafast optical fields

Vadym Apalkov and Mark I. Stockman

Phys. Rev. B 88, 245438 – Published 26 December 2013

Abstract

We predict that a metal nanofilm subjected to an ultrashort (near-single oscillation) optical pulse of a high field amplitude $≳$ $3 V / Å$ at normal incidence undergoes an ultrafast (at subcycle times $≲$ $1 fs$ ) transition to a state resembling semimetal. Its reflectivity is greatly reduced, while its transmissivity and the optical field inside the metal are greatly increased. Despite the metal being a centrosymmetric medium, the strong pulse causes net charge transfer in the direction determined by the carrier envelope phase (CEP) of the pulse, which is opposite to the direction of the maximum field.

Received 8 September 2012
Revised 26 October 2013

DOI:https://doi.org/10.1103/PhysRevB.88.245438

Authors & Affiliations

Vadym Apalkov¹ and Mark I. Stockman^1,2,3

¹Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, USA
²Fakultät für Physik, Ludwig-Maximilians-Universität, Geschwister-Scholl-Platz 1, D-80539 München, Germany
³Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany

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Issue

Vol. 88, Iss. 24 — 15 December 2013

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Images

Figure 1
Reflected and transmitted pulses. (a) Spatial distributions of the electric field as functions of the propagation coordinate $z$ shown for different values of $F_{0}$ . The metal film of thickness 25 nm is placed at the center ( $z = 0$ ) and depicted as the red stripe. The distribution of electric field consists of the reflected (to the left) and transmitted (to the right) pulses propagating in the opposite directions. The size of the computational field in the $z$ direction is 6000 nm. (b) Spectral intensities of reflected, transmitted, and sum pulses for $F_{0} = 7.7 V / Å$ as functions of optical frequency $f = ω / (2 π)$ . The transmitted- and sum-pulse spectra are arbitrarily normalized to unity maximum. The reflected pulse spectrum is normalized by the same coefficient as the transmitted one. Fragments of the curves at $f > 2 PHz$ are also shown with the $\times$ 10 magnification as indicated on the graph.
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Figure 2
The electric field of the incident pulse (black lines) and the electric field at the midpoint of the metal film (red line) are shown for different values of the peak electric field $F_{0}$ of the incident pulse: (a) $F_{0} = 3.4$ , (b) $4.3$ , and (c) $6.0$ V $/ Å$ . Note that the pulse areas are nonzero, cf. discussion of Fig. 1, which causes net current and charge transfer along the metal in the $x$ direction.
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Figure 3
(a) The reflectance of optical pulse (black line) and the maximum electric field at the midpoint of the nanofilm (red line) are shown as functions of the peak electric field $F_{0}$ of the incident pulse. The maximum electric field in the metal film is shown in units of the peak electric field $F_{0}$ . (b) The absorbance of the optical pulse is shown as a function of the peak electric field $F_{0}$ .
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Figure 4
Bloch oscillations in the transmitted field and electron momentum. (a) Electric field distribution in space of the transmitted optical pulse is shown for different values of $F_{0}$ . (b) The corresponding dimensionless time-dependent wave vectors in the first Brillouin zone $a k_{T} (q = 0, t)$ as functions of time $t$ . The origin of time is chosen arbitrary, and the graphs are offset vertically for clarity.
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Figure 5
Excitation pulse waveforms $F_{x} (t, ϕ)$ for $F_{0} = 1 V / Å$ and four choices of the CEP, $ϕ = 0, π / 4, π / 2, 3 π / 2$ (as indicated).
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Figure 6
Charge transferred as a result of a single pulse as a function of the carrier-envelope phase (CEP) of the pulse. The results are shown for three pulse amplitudes $F_{0}$ as indicated in the figure using color coding.
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