Efficient transfer of light energy to a nanoparticle by means of a resonance atomic lens
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Efficient Transfer of Light Energy to a Nanoparticle by Means of a Resonance Atomic Lens G. N. Nikolaev Institute of Automation and Electrometry, Siberian Division, Russian Academy of Sciences, Universitetskii pr. 1, Novosibirsk, 630090 Russia e-mail: [email protected] Received April 15, 2005
Abstract—A cascade transfer of light energy to a resonance atom situated near a spherical nanoparticle and then, by a nonradiative mechanism, to the nanoparticle itself is considered. It is established that the efficiency of the cascade transfer essentially depends on the frequency and polarization of light, on the distance between the atom and the particle, on the optical properties of the particle, and on the time conditions of radiation. The rate of light absorption by a metal nanoparticle via cascade energy transfer may be 104–105 times higher than the direct absorption of light by a nanoparticle. For a fixed frequency of light, the cascade transfer of energy is a sharply selective function of the distance between the atom and the particle (the resonance width is about 10−2 of the particle radius). Atomic fluorescence exhibits similar behavior. This feature can form the basis for a new method of optical scanning microscopy and location and localization of atoms near the surface of a particle. PACS numbers: 42.50.Ct, 12.20.–m, 42.60.Da, 42.50.Lc, 42.50.Pq, 42.50.Nn DOI: 10.1134/S1063776106030034
1. INTRODUCTION The absorption cross section of an isolated spherical particle with radius a much less than the wavelength λ of the incident light (a/λ 1) is defined by the classical formula [1] a '' ε h σ p = 24π --- ----------------S, λ +22
2. ABSORPTION OF ENERGY OF A CLASSICAL OSCILLATING DIPOLE
(1)
where S = πa2, ≡ εp/εh = ' + i'' is the relative permittivity of the particle, and εp and εh are the permittivities of the particle and the surrounding medium, respectively. As a rule, σp is less than the geometrical cross section S. On the other hand, it is well-known that the cross section of the resonant interaction between an atom and light is much greater: 1 γ 0h 2 -λ , σ a = ------ -----2π γ
transfer of light energy to an atom and, from the latter, to a particle. A part of the results presented below was sketched in [5, 6].
From the classical viewpoint, a transfer of energy from an atom excited by light to a particle occurs due to
S Atom
(2)
where γ0h and γ are the radiative and total halfwidths of the resonance transition of an atom in a homogeneous medium. Note that γ0h is expressed in terms of the rate of spontaneous transition of an atom in vacuum, γ0, by the formula γ0h ≡ ε h |(εh + (see, for example, [2–4]). As a rule, σp σa (Fig. 1). The goal of the present paper is to carry out a detailed investigation of the possibility of the cascade 2)/3|2γ0
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σa σp σp σa Fig. 1. Schematic representation of the cascade transfer of energy to a nanoparticle by means of an “atomic lens.”
EFFICIENT TRANSFER OF LIGHT ENERGY TO A NANOPARTICLE
the work done by the electric and magnetic fields of
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