Near-field effect in optics of small objects composed of dipole atoms

A self-consistent problem of interaction of two dipole atoms separated by an unrestricted distance with the field of a quasi-resonance light wave was solved on the assumption that the investigated atoms are Lorentz linear oscillators and the polarizing fields inside the system consist of the Coulomb and the retarded parts. The solution obtained was investigated for the case where the atoms have the same polarizability and the distance between them is much smaller than the length of the external light wave. Formulas for the electric fields inside a small object and outside it have been obtained. It is shown that inside a small two-atom object there can take place longitudinal and transverse optical vibrations accompanied by corresponding dispersion effects depending on the interatomic distance and the angle between the axis of the system and the direction of propagation of the external light wave. The field outside the small object in the wave zone is linearly polarized when the external wave has linear polarization. However, the direction of polarization of the corresponding waves is largely determined by their frequency. It is also shown that the amplitude of the field outside the small object in the wave zone depends greatly on the frequency of the external field and the interatomic distance. The effects observed are considered as a near-field effect in optics of small objects. This phenomena makes it possible to investigate the structure of small objects with the use of optical radiation. Ul'yanovsk Branch of the Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 48 Goncharov Str., Ul'yanovsk, 432700, Russia; e-mail: gadomsky@quant.univ.simbirsk.su. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 765–770, November–December, 1999.     

The near-field effect in a system of two-level dipole particles

We have solved a self-consistent problem on interaction of two dipole atoms located at an arbitrary distance from each other with the field of a quasiresonance light wave, whose intensity is sufficient for the system to manifest nonlinear properties. The atoms are considered as two-level systems described by means of Bloch optical equations, while the field inside of the system includes both Coulomb and retarded parts. We consider a situation where atoms are identical and the distance between them is much smaller than the length of an outer light wave. The distribution of an electric field both inside of a small object and outside of it is found numerically. It is shown that the amplitude of the electric field in a wave zone depends substantially on the frequency of the external field and interatomic distance, while the field distribution differs from the field pattern of an electric dipole. At definite values of the external field intensity an optical multistability is a feature of the system under investigation. We have elucidated the conditions under which the multistability is manifested in the present system. The results obtained are considered as the near-field effect in the optics of small objects, which makes it possible to investigate the structure of small objects by means of optical radiation. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 375–378, May–June, 2000. The present work was supported by the Russian Foundation for Fundamental Research (grant 98-02-16035) and by a grant from the Federal Purpose-Oriented Program “Integration.”     

Method of resonance near-field optical microscopy

We have solved the problem in which a thin metal wafer (probe) with a nanohole interacts with the flat surface of a metastructured film consisting of metal nanoparticles in an external optical radiation field. Nanoparticles are considered as two-level atomic systems. This interaction of the wafer-probe and the flat surface in the external optical radiation field gives rise to optical near-field resonance, the frequency of which differs significantly from the natural frequencies of two-level atoms in the medium and the probe. The fields inside and outside the probe and metastructured film are calculated in the near-field and far-field zones. The maximum resolution, which is achievable in the suggested scheme of near-field optical microscopy, can reach about 10 nm. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 499–506, July–August, 2007.     

Boundary-value problems in near-field optical microscopy and optical size resonances

We have solved a boundary-value problem for a ball probe interacting with a flat dielectric surface in an external optical radiation field. This interaction gives rise to the optical size resonance at frequencies significantly different from the natural frequencies of two-level atoms both in the medium and in the probe with allowance for the local field corrections. These resonances depend significantly on the distance from the probe center to the surface, on the ball probe size, on the concentration of two-level atoms in the probe and in the medium, on the spectral line width, and on the atomic inversion. The field strengths inside and outside the ball probe and a semiinfinite dielectric medium have been calculated in the near-field and wave zones. It is shown that the proposed electrodynamic theory of optical near-field microscopy agrees with the results of experimental measurements.     

Light scattering by nanosized systems with different spatial organizations

The integrodifferential equation method is used to study the spectrum of a nanoparticle colloid for the example of interaction of three arbitrarily arranged dielectric particles made up of nonresonant atoms (the eigenfrequency of the transition is far from the emission frequency) with incorporated barium atoms in an external optical radiation field. The effect on the light-scattering properties of a nanosphere in the ensemble of its distant “neighbors” is studied; an additional peak associated with them is observed as a frequency close to the resonance for an isolated nanosphere, which under certain conditions has higher intensity than the main peak corresponding to optical near-field resonance in a two-particle system. The dependence of the spectrum of the nanosized system on the geometric structure is studied, and it is shown that very precise tuning of the resonance frequency is possible by varying the angular distribution of the particles. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 641–646, September–October, 2006.     

Electrodynamics with an integer charge and topology

An approach to constructing electrodynamics with an integer charge based on its topological interpretation is considered in the present paper. The condition that changes are integers is shown to endow the space itself with a variable permittivity. It is demonstrated that the concept suggested here solves the main problems of electrodynamics associated with point charges and provides a simple topological classification of field structures compared to that of the main elementary particles, including baryons. Electrodynamics equations of integer-charge fields are derived. Ul'yanovsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 8–13, January, 2000.     

One-and two-front states of equilibrium in a thin superconducting film

Two-phase states of equilibrium of a thin superconducting film carrying a current under conditions of convective heat exchange at the free surface of the film are studied. It is shown that for a classical superconductor the two-phase state of the film remains a single-front state over a wide range of parameters of the system. For high-T _c superconductors there exists a maximum value of the Steckl number above which weakly nonequilibrium stationary states can only be multifront states. The solutions of the boundary-value problem modeling a two-front state of equilibrium are investigated, and the conditions under which they obtain are examined. Zh. Tekh. Fiz. 68, 84–87 (March 1998)     

Two-photon interaction of coherent radiation with a thin film of resonant atoms

The problem of the interaction of an ultrashort optical pulse and a thin film of resonant atoms under the conditions of two-photon absorption, third-harmonic generation, and the inverse effect of the latter on the pump pulse via Raman scattering is studied. The fact that the field acting on an atom differs from the macroscopic field in the film is also taken into consideration. It is shown that the polarization of the film undergoes dynamic relaxation even in the absence of irreversible relaxation, suppressing Rabi oscillations and establishing stationary values of the populations of the resonant energy levels and of the polarization of the film at the pump and the third-harmonic frequencies. Zh. éksp. Teor. Fiz. 115, 30–42 (January 1999)     

Intercalation of two-dimensional graphite films on metals by atoms and molecules

An analysis is made of some general laws governing a new physical effect, i.e., the spontaneous penetration of particles (atoms, C₆₀ molecules) adsorbed on a two-dimensional graphite film on a metal (Ir, Re, Pt, Mo,...) to beneath the graphite film (intercalation). It is shown that atoms having low ionization potentials (Cs, K, Na) intercalate a two-dimensional graphite film on iridium at T=300–400K with an efficiency χ≈0.5, accumulating beneath the film to a concentration of up to a monolayer. Atoms having high ionization potentials (Si, Pt, Ni, C, Mo, etc.) intercalate a two-dimensional graphite film on iridium at T≈1000K with an efficiency, χ≈1, forming beneath the film a thick intercalate layer which is strongly bonded chemically to the metal substrate but is probably weakly bonded to the graphite monolayer by van der Waals forces. The presence of a graphite “lid” impeding the escape of atoms from the intercalated state up to record high temperatures T∼2000K leads to superefficient diffusion (with an efficiency close to one) of various atoms (Cs, K) into the bulk of the substrate (Re, Ir). Zh. Tekh. Fiz. 69, 72–75 (September 1999)     

Electrodynamic response of a colloid ensemble with allowance for the influence of distant nanoparticles

The optical properties of a colloid consisting of nanoparticles are investigated on the example of interaction of three dielectric particles consisting of nonresonant atoms (whose natural transition frequencies are far from the radiation frequency) with interstitial barium atoms in the field of external optical radiation. On the basis of integrodifferential equations, expressions for the electric and magnetic fields in the wave zone are derived. The influence of distant neighbors in the ensemble on the light-scattering properties of a nanoparticle is considered, and the condition of applicability of the frequently used two-particle approximation is obtained. The spectrum of the system is investigated, and an additional resonant peak at the natural frequency of the isolated particle caused by the distant neighbor is established. Under some specific conditions, the additional peak intensity may exceed the main peak intensity of the optical near-field resonance in the two-particle system. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 3–11, August, 2006.     

Light-Induced shifts in the frequency of a multiphoton radiooptical SHF resonance in alkali atoms

A computation is carried out for light-induced shifts in the frequency of a multiphoton radiooptical SHF resonance in alkali atoms on the basis of the quantum formalism of spherical tensors. The components of a light-induced shift in frequency at magneto-independent 0–0– and 1,–1-transitions in⁸⁷Rb atoms under the conditions of isotopic filtration of the resonance light of pumping are calculated. The difference between the temperatures of a filter cell is discovered at which the point of zero shift in the frequency of radiooptical resonance is attained. The components of the light-induced shift of frequency in optically oriented⁸⁷Rb and¹³³Cs atoms are compared in the absence of collisional reorientation in excited state. The prevailing role of the tensor component of light-induced shift in pumping by the D₁-line of a head doublet and the effect of the orientational dependence of the frequency of a multiphoton resonance on change in the sign of the pumping source radiation polarization are noted. St. Petersburg State Polytechnical University, 29 Politekhnicheskaya Str., St. Petersburg, 195251, Russia. Translated from Zburnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 832–838, November–December, 1998.     

Spontaneous emission from an atomic oscillator located near an ideally conducting conical surface

The linewidth for an atom located near an ideally conducting tip or inside a conical cavity in an ideal conductor is analyzed. It is shown that the effect of the tip decreases as its opening angle decreases. At the same time, the linewidth for an atom in a conical cavity can strongly increase or strongly decrease, depending on the position of the atom and the opening angle of the cavity. The results obtained could be helpful in designing spectrally-selective near-field nanoscopes. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 8, 610–613 (25 October 1998)     

Reflection and refraction of light by a system of interfering atomic states

The boundary problem of nonlinear optics was investigated for a trial wave reflected (refracted) by an excited region of a nonlinear medium considered as a system of multilevel atoms in the spectrum of which there are two closely-spaced energy levels excited by a powerful quasi-resonant radiation. It is shown that under interference conditions of the atomic states in the field of the trial and resonance waves there exist three types of waves: an inverse wave and two polarization waves. By way of extension of the Ewald-Oseen procedure to this case a formula for the complex refractive index of a nonlinear medium for the three types of waves as well as a generalized extinction theorem have been obtained. It is shown that the trial wave can be amplified without inversion of the interfering atomic states and that the refractive index can be markedly changed at certain concentrations of atoms in the medium. General formulas for the amplitudes of the reflected and refracted waves have been obtained. Ul’yanovsk State University, 42, Tolstoi Str., Ul’yanovsk, 432700, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 568–575, July–August, 1998.     

Waveguide properties of a four-layer planar structure with an absorbing coating layer

An exact solution is obtained and a problem of waveguide light propagation in a scalar asymmetric four-layer waveguide with an absorbing coating layer is analyzed numerically. The periodicity of modal characteristics with change in the coating layer thickness is established. The feasibility of achieving a single-mode light propagation regime at the expense of the absorbing coating layer is demonstrated. Ul'yanovsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 79–85, July, 2000.     

Radiation from a small spheroidal antenna with plasma shell

We construct and study an analytical solution of the boundary-value problem for the radiation field of a small spheroidal antenna located in free space and surrounded by a thin shell of cold homogeneous isotropic plasma. Conditions for a resonant increase in the field in free space as a function of the plasma-shell thickness with the variation in the spheroidal-antenna shape are studied. It is shown that the plasma shell has the largest effect on the radiation field of a strongly prolate spheroidal antenna. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 3, pp. 246–257, March 2006.     

Formation of quasi-free graphene on the Ni(111) surface with intercalated Cu,Ag, and Au layers

This paper reports on a study by angle-resolved photoelectron and low-energy electron energy loss spectroscopy of graphene monolayers, which are produced by propylene cracking on the Ni(111) surface, followed by intercalation of Cu, Ag, and Au atoms between the graphene monolayer and the substrate, for various thicknesses of deposited metal layers and annealing temperatures. It has been shown that the spectra of valence-band π states and of phonon vibrational modes measured after intercalation become similar to those characteristic of single-crystal graphite with weak interlayer coupling. Despite the strong coupling of the graphene monolayer to the substrate becoming suppressed by intercalation of Cu and Ag atoms, the π state branch does not reach at the K point of the Brillouin zone the Fermi level, with the graphene coating itself breaking up partially to form graphene domains. At the same time after intercalation of Au atoms, the electronic band structure approaches the closest to that of isolated graphene, with linear π-state dispersion near the K point of the Brillouin zone, and the point of crossing of the filled, (π), with empty, (π*), states lying in the region of the Fermi level, which makes this system a promising experimental model of the quasi-free graphene monolayer.     

Elemental and phase composition analysis of hydrogen-sensitive Pd/Mg–Ni films

A magnesium–nickel (Mg–Ni) film with a palladium (Pd) overcoat is switchable between a conducting metallic state and a semiconducting state through hydridation and dehydridation processes. The Pd overcoat is added to suppress possible oxidation of the alloy layer. However, some Pd and oxygen (O) atoms are still able to diffuse into the alloy layer, such that the distributions of elemental and phase compositions along the direction of depth are quite complicated. In this work, we propose a method to obtain more detailed information on the elemental and phase compositions in a Pd/Mg–Ni film by means of analyzing Pd 3d_5/2, Pd 3p_3/2, Ni 2p_3/2, Mg 1s and O 1s photoelectron spectra. The method was applied to analyze a typical Pd/Mg–Ni film sample. Results verified that Pd can diffuse into the alloy layer. An Mg–O phase is formed near the surface. An Mg–Ni alloy phase dominates at deeper regions. The Mg–Ni phase contains 80% of the total number of atoms in the film, and is non-stoichiometric and highly disordered. Nevertheless, it can give a remarkable change of electrical resistivity during hydridation–dehydridation processes. PACS 79.60.-i; 61.05.C-; 79.60.Ht     

A Monatomic Optical Near-Field Microscope with Subnanometer Spatial Resolution

We propose the principle of operation of an optical near-field microscope on the basis of linear steady-state optical dimensional resonances in the system atom-probe–atoms of the sample. It is shown that such a microscope has high sensitivity and a spatial resolution of less than 1 nm and does not set limits on the choice of samples. The distribution of the optical fields in the wave and near zones in the near-field microscope at frequencies close to the optical dimensional resonances arising as a result of dipole-dipole interactions of atoms at small distances has been investigated. The optical scheme of the monatomic near-field microscope is presented.