Super scattering phenomenon in active spherical nanoparticles

Localized surface electromagnetic resonances in spherical nanoparticles with gain are investigated by using the Mie theory. Due to the coupling between the gain and resonances, super scattering phenomenon is raised and the total scattering efficiency is increased by over six orders of magnitude. The dual frequency resonance induced by the electric dipole term of the particle is observed. The distributions of electromagnetic field and the Poynting vector around nanoparticles are provided for better understanding different multipole resonances. Finally, the scattering properties of active spherical nanoparticles are investigated when the sizes of nanoparticles are beyond the quasi-static limit. It is noticed that more highorder multipole resonances can be excited with the increase of the radius. Besides, all resonances dominated by multipole magnetic terms can only appear in dielectric materials.     

Effect of a weak magnetic field on resonant features of conductance in an open circular billiard with Dresselhaus spin-orbit interaction

The effect of a weak magnetic field on the transport properties of an open circular billiard with attached channels in the presence of Dresselhaus spin-orbit interaction are considered. It is shown that the application of a magnetic field leads to splitting of the Fano resonances, which were found earlier on the energy dependence of conductance, into pairs of resonances with half lower amplitudes. The relationship between the energy values to which these resonances collapse when the spin-orbit interaction is absent, and the levels of the energy spectrum in the corresponding closed billiard has been established. It is shown also that the applied magnetic field induces a qualitative change in the spin polarization of a wave in the output channel.     

Effect of a stray magnetic field on nonlinear magneto-optical resonances observed in the geometry of counter-propagating light waves

Magneto-optical resonances of electromagnetically induced absorption (EIA) in a cell filled with the vapor of alkali atoms and buffer gas are considered. The atoms are excited using a configuration of electromagnetic fields composed of two counter-propagating linearly polarized light waves and a static magnetic field. We focus on the influence of the residual magnetic field on the parameters of nonlinear resonances. In real experiments, a residual field is always present in the cell due to imperfect magnetic-field shielding. On the basis of calculations, we formulate practical recommendations for controlling the residual magnetic field in the experiments aimed at observation of high-quality EIA resonances. The results from this work can find application in quantum magnetometry and nonlinear optics.     

Coherent population trapping spectra in presence of ac magnetic fields

Experimental and theoretical investigations are reported on the effects induced by an alternating magnetic field on coherent population trapping resonances. We show that the ac magnetic field produces sidebands of these resonances in such a way that the spectrum observed is similar to those observed via the FM spectroscopic technique. Because of the very narrow linewidth of the resonances, sidebands are resolved even for ac field frequencies as low as a fraction of a kHz. The theoretical model developed, which takes into account a very simple atomic structure, fits the experimental data quite well.     

Deformation of magneto-optical structures in radiation of extended sources

Shape distortions of magneto-optical resonances in emission of an extended source are considered. The shape deformation of the magneto-optical structures is shown to be created by a longitudinal spatial inhomogeneity of the magnetic field. A simple procedure of taking into account distortions and of determining positions of resonances on the magnetic field scale and their widths is proposed.     

Gravitational Waves Interacting with a Spinning Charged Particle in the Presence of a Uniform Magnetic Field

The equations which determine the response of a spinning charged particle moving in a uniform magnetic field to an incident gravitational wave are derived in the linearized approximation to general relativity. We verify that 1) the components of the 4-momentum, 4-velocity and the components of the spinning tensor, both electric and magnetic moments, exhibit resonances and 2) the co-existence of the uniform magnetic field and the GW are responsible for the resonances appearing in our equations. In the absence of the GW, the magnetic field and the components of the spin tensor decouple and the magnetic resonances disappear.     

Cyclotron resonance of inversion electrons on InSb in tilted magnetic fields

Cyclotron resonance (CR) of inversion electrons on InSb is studied in magnetic fields tilted away from the surface normal. Particularly, a pronounced splitting of the CR signals into two distinct resonances is observed. When the magnetic field is parallel to the inversion layer one of the two resonances vanishes and the other evolves into a bulk like CR at sufficiently low electron densities and in sufficiently high resonance magnetic fields. The different absorption modes are explained by a strong coupling of the electric and magnetic quantization on InSb in tilted magnetic fields.     

Optical magnetic resonances induced by the interference of reactive components in the near radiation-field zone of atoms in a glow discharge of a mixture of even neon isotopes

Four types of anomalous optical magnetic resonances shifted with respect to the zero magnetic field and with different shapes are found in radiation of a glow discharge in a mixture of even neon isotopes placed in a swept longitudinal magnetic field. This testifies to the manifestation of collective processes of synchronous light emission by oscillators belonging to isotopically different spatially separated atoms in discharge plasma. The origin of resonances is associated with nonstationary interference of reactive fields in the near radiation-field zones of emission of atoms, averaged over the lifetime of the fields (interference), while different types of resonances are associated with different methods of synchronization of the phases of the fields.     

Magnetooptic resonances in dichroism and birefringence related to the self-alignment of atoms in a discharge at an arbitrary orientation of the magnetic field

Variations in structure of the magnetooptic resonances, formed by a transverse magnetic field in the presence of an additional field of arbitrary orientation, are analyzed. These resonances are shown to be sensitive to the type of excitation anisotropy. The ways of detecting false magnetic fields are proposed.     

Inspection of a magneto-optical trap via electromagnetically induced absorption

Electromagnetically induced absorption (EIA) was observed for the first time on a sample of ⁸⁵Rb in a magneto-optical trap using low intensity cw copropagating pump and probe optical fields. Narrow resonances revealing the dependence of the ground-state Zeeman sublevels energy structure on the quadrupolar magnetic field and the trapping optical field intensity at different trap positions, were observed. Coherence resonances as narrow as 30 kHz were obtained under low trapping field intensities. The use of EIA spectroscopy for the magnetic field mapping of cold atomic samples is illustrated.     

Electric and magnetic excitations in anisotropic broadside-coupled triangular-split-ring resonators

The electric and magnetic resonances of anisotropic broadside-coupled triangular-split-ring resonators are studied for different incident wave excitations. It is shown that the higher order modes exist in both electric and magnetic resonances. It is observed that the incident electric field couples to the magnetic resonance of the designed structure under different excitations. Multiple resonance features due to the anisotropy of the structure are found in the case of different excitations and the nature of these resonances can be regulated as either an electric or a magnetic mode for different frequencies. In this way, a resonant effective permittivity or permeability can be obtained. Hence, controllable properties of the constitutive material parameters (i.e. electric or magnetic resonances, negative values, etc.) can be determined by changing the incident wave excitation.     

Onset and saturation of ion heating by odd-parity rotating magnetic fields in a field-reversed configuration

Heating of figure-8 orbit ions by odd-parity rotating magnetic fields (RMF(O)) applied to an elongated field-reversed configuration (FRC) is investigated. The largest energy gain occurs at resonances (s congruent to omega(R)/omega) of the RMF(O) frequency, omega(R), with the figure-8 orbital frequency, omega, and is proportional to s2 for s-even resonances and to s for s-odd resonances. The threshold for the transition from regular to stochastic orbits explains both the onset and saturation of heating. The FRC magnetic geometry lowers the threshold for heating below that in the tokamak by an order of magnitude.     

Determination of the structure of hyperfine sublevels of Rb in strong magnetic fields by means of the coherent population trapping technique

The splitting of hyperfine sublevels of the ⁸⁵Rb atom in strong magnetic fields has been studied by means of the coherent population trapping technique. Narrow resonances with a high signal-to-noise ratio have been detected in a 30-μm-thick spectroscopic cell. The magnetic field in the direction transverse to the laser beams has been created by permanent magnets and has reached 1600 G. Owing to the exclusive narrowness of the cell, the field in it is almost uniform. The break of the coupling between the electronic and nuclear moments, as well as the transition to the Paschen-Back regime in magnetic fields above 600 G, has been observed. The derivatives of the frequency shifts of the observed resonances and their asymptotic values in strong magnetic fields have been determined in terms of the magnetic field strength. The experimental results have been interpreted within a theoretical model based on the known constants of the hyperfine structure of the Rb atom.     

Ultracold RbSr molecules can be formed by magnetoassociation

We investigate the interactions between ultracold alkali-metal atoms and closed-shell atoms using electronic structure calculations on the prototype system Rb+Sr. There are molecular bound states that can be tuned across atomic thresholds with a magnetic field and previously neglected terms in the collision Hamiltonian that can produce zero-energy Feshbach resonances with significant widths. The largest effect comes from the interaction-induced variation of the Rb hyperfine coupling. The resonances may be used to form paramagnetic polar molecules if the magnetic field can be controlled precisely enough.     

Identification of anomalous optical magnetic resonances in the total emission of a mixture of neon isotopes

In the dependence of the emission of a glow discharge in a mixture of isotopes ²⁰Ne and ²²Ne on the longitudinal magnetic-field strength, we have revealed narrow resonances, while the waves have non-Lorentzian shapes and are shifted with respect to zero field. Variations in the concentration of isotopes and discharge current can vary the amplitude, the shape, and the number of resonances; however, the position of each of them on the scale of the magnetic field almost does not depend on the spectral composition of the registered emission. We have elucidated a relation between the positions of the resonances on the scale of the magnetic field and the isotope shifts of neon transitions.     

Emission anomalous optical magnetic resonances in a mixture of even neon isotopes

Unusual resonances have been detected in the dependence of the discharge glow in neon on the longitudinal magnetic field. The resonances appear in fairly high magnetic fields and are observed only at low gas pressures and exclusively in a mixture of ²⁰Ne and ²²Ne isotopes. This phenomenon is an evidence of collective resonant radiation processes involving atoms of different neon isotopes.     

Collision of atoms under action of external magnetic and laser radiation fields with formation of Fano-Feshbach resonances

We investigate collision of two atoms in an external magnetic field and in the field of laser radiation with formation of Fano-Feshbach resonances. At one-photon resonance of laser radiation with two discrete vibrational states of molecule the dressed states are formed (Autler-Townes effect) which form Fano-Feshbach resonances in interaction with the external magnetic field. In addition, the lower molecular vibrational state is coupled with the continuum of the elastic channel via also LICS (laser-induced continuum structure) forming laser-induced resonance. We obtain cross-sections of elastic and inelastic resonant scattering and expression for the scattering length depending on the external magnetic and laser radiation fields.     

Study of EIT resonances in an anti-relaxation coated Rb vapor cell

We study the sign of resonances obtained in electromagnetically induced transparency (EIT). Resonances of both kinds—bright (corresponding to enhanced absorption) and dark (corresponding to reduced absorption)—are obtained when the frequency of a probe beam is scanned. The experimental results, presented earlier, use magnetic sublevels of a hyperfine transition in the D₁ line of ⁸⁷Rb along with a magnetic field of 27 G. The atoms are contained in a vapor cell at room temperature, and with anti-relaxation coating on the walls. A quantitative theoretical model, which reproduces the experimental results quite well, is presented for the first time. The model solves the density matrix of the sublevels involved, and uses two regions—one with both the light and magnetic field, and the second without light and just a magnetic field. This ability to have both bright and dark resonances promises applications in sub- and super-luminal propagation of light.     

Handedness of magnetic-dipolar modes in ferrite disks

For magnetic-dipolar modes in a ferrite, components of the magnetic flux density in a helical coordinate system are dependent on both an orientation of a gyration vector and a sign of a pitch. It gives four types of helical harmonics for magnetostatic-potential wave functions in a ferrite disk. Because of the reflection symmetry breaking, coupling between certain types of helical harmonics takes place in the reflection points. The reflection feature leads to exhibition of two types of resonances: the “right” and “left” resonances. These resonances become coupled for a ferrite disk placed in a homogeneous tangential RF magnetic field. One also observes such resonance coupling for a ferrite disk with a symmetrically oriented linear surface electrode, when this ferrite particle is placed in a homogeneous tangential RF electric field. In a cylindrical coordinate system handedness of magnetic-dipolar modes in a ferrite disk is described by spinor wave functions.     

Nonlinear resonances free of field and doppler broadenings

For the case where the Rabi frequencies of the guiding fields are much larger than the relaxation constants but much smaller than the Doppler broadening, it is shown that resonances which are neither field nor Doppler broadened can appear in the absorption (or gain) spectrum of the probe field. A classification of four-level systems according to the number of resonances is made for cases where two strong fields interact either with opposite or adjoining transitions. The conditions under which the number of resonances reaches eight, while for stationary atoms the maximum number is four, are found. A method is proposed for calculating the number of resonances in a multilevel system with several strong fields using analysis of the extremum points of the frequency branches in the velocity-frequency plane.