A. V. Dorofeenko

Optical Tamm States in One-Dimensional Magnetophotonic Structures

We demonstrate the existence of a spectrally narrow localized surface state, the so-called optical Tamm state, at the interface between one-dimensional magnetophotonic and nonmagnetic photonic crystals. The state is spectrally located inside the photonic band gaps of each of the photonic crystals comprising this magnetophotonic structure. This state is associated with a sharp transmission peak through the sample and is responsible for the substantial enhancement of the Faraday rotation for the corresponding wavelength. The experimental results are in excellent agreement with the theoretical predictions.

Steady state superradiance of a 2D-spaser array

We demonstrate that a 2D array of spasers may be synchronized. Since in the sole spaser the joule losses exceed radiation ones it is the near fields of surface plasmons that are amplified. In the array of synchronized spasers due to superradiance the radiation of photons prevails over the joule losses and spasers start working as nanolasers. Since the synchronization is due to near field interaction the system size may be greater than the wavelength, opposite to the case of usual supperradiance. Thus, the aperture of the system may be chosen greater than wavelength that results in narrowing of the radiation pattern and in cubic dependence of the intensity on the number of spasers.We show that due to near-field interaction of plasmonic particles via gain particles, a two-dimensional array of incoherently pumped spasers can be self-synchronized so that the dipole moments of all the plasmonic particles oscillate in phase and in parallel to the array plane. The synchronized state is established as a result of competition with the other possible modes having different wavenumbers and it is not destroyed by radiation of leaking waves, retardation effects, and small disorder. Such an array produces a narrow beam of coherent light due to continuous-wave superradiance. Thus, spasers, which mainly generate near-fields, become an efficient source of far-field radiation when the interaction between them is sufficiently strong.

Spectrum of surface plasmons excited by spontaneous quantum dot transitions

We consider quantum fluctuations of near fields of a quantum emitter (two-level system (TLS) with population inversion sustained by incoherent pumping) in the near-field zone of a plasmon (metallic) nanoparticle. The spectrum of surface plasmons excited by spontaneous transitions in the quantum emitter is obtained below the lasing threshold of such a system (spaser) in the approximation of a small number of plasmons. It is shown that the relaxation rate is the sum of the quantum emitter’s rates of relaxation to its thermal reservoir and the plasmon cavity. The resulting dependence of the average number of plasmons on the pump intensity indicates the nonthreshold nature of the process.

Dynamics of the transient regime of spaser

The dynamics of the nonradiative excitation of plasmons in the surface plasmon amplifier by stimulated emission of radiation (spaser) that represents a two-level quantum dot in the vicinity of the metal (plasmon) nanoparticle is considered. It is demonstrated that the steady-state generation of spaser is preceded by the regime with the oscillations at the Rabi frequency in which the phase difference between the dipole moments and the direction of the energy flux from the quantum dot to the nanoparticle exhibit the sign alternation.

Modification of the Resonance Fluorescence Spectrum of a TwoLevel Atom in the Near Field of a Plasmonic Nanoparticle

The resonance fluorescence spectrum of an atom located in the near field of a plasmonic nanoparticle is considered. It is shown that, as the atom gets close to the nanoparticle, the high-frequency peak of the Mollow triplet disappears and the spectrum has a Fano resonance shape. The low-frequency peak also disappears as the distance between the atom and the nanoparticle decreases further. For small distances, when the atom interacts with the nanoparticle much more strongly than with the external field, the spectrum represents a Lorentzian line whose width is proportional to the square of the atom-nanoparticle coupling constant.

Lasing in a gain slab as a consequence of the causality principle

Transmission of a semi-infinite light pulse through a slab of an gain medium is considered. It is demonstrated that, in the presence of lasing, the Fresnel formulas yield a finite field distribution violating the causality principle: lasing in the slab begins starts the moment at which the pulse front reaches the slab. A modification of the Fresnel approach providing for causality through adding time-diverging terms for description of the linear stage of lasing is proposed. The correctness of the proposed approach is proved by the comparison with the numerical solution of the system of Maxwell-Bloch equations. It is shown that fulfillment of lasing conditions does not contradict the causality principle.

Frequency Control of the Microwave Tamm State

Tunneling of microwave radiation through the surface Tamm state that is generated at the interface between two different periodic structures (photonic crystals) has been studied theoretically and experimentally. The possibility of controlling the transmission frequency of this system with the use of an external magnetic field has been predicted theoretically and confirmed experimentally.

Forced Spaser Oscillations

We study oscillations of a spaser driven by an external optical wave. When the frequency of the external field is shifted from the frequency of an autonomous spaser, the spaser exhibits stochastic oscillations at low field intensity. The plasmon oscillations lock to the frequency of the external field only when the field amplitude exceeds a threshold value. We find a region of external field amplitude and the frequency detuning (the Arnold tongue) for which the spaser becomes synchronized with the external wave. We obtain the conditions upon the amplitude and frequency of the external field (the curve of compensation) at which the spaser’s dipole moment oscillates with a phase shift of π relatively to the external wave. For these values of the amplitude and frequency, the loss in the metal nanoparticles within the spaser is exactly compensated for by the gain. It is expected that if these conditions are not satisfied, then due to loss or gain of energy, the amplitude of the wave travelling along the system of spasers either tends to the curve of compensation or leave the Arnold tongue. We also consider cooperative phenomena showing that in a chain of interacting spasers, depending on the values of the coupling constants, either all spasers oscillate in phase or a nonlinear autowave travels in the system. In the latter scenario, the traveling wave is harmonic, unlike excitations in other nonlinear systems. Due to the nonlinear nature of the system, any initial distribution of spaser states evolves into one of these steady states.

Spaser operation in the presence of external optical field

The operation of surface plasmon amplifier by stimulated emission of radiation (spaser) in the presence of external optical field is analyzed. The range of external field amplitude E and mismatch Δ of the external field frequency and the spaser generation frequency (Arnold tongue) E > Esynchr(Δ) in which the spaser works at the external field frequency is determined. The analytical and numerical calculations at the given mismatch Δ yield three ranges: E < Esynchr(Δ) (the spaser exhibits stochastic regime and point (Δ, E) is outside the Arnold tongue), Esynchr(Δ) < E < EL(Δ) (transient range where the spaser polarization weakly depends on the field amplitude and is mainly determined by the pump level), and E > EL (the spaser generation is suppressed and the spaser polarization is equal to the polarization of nanoparticle in the presence of external field).

Plasmons in Chains of Spherical Nanoparticles with the Account of All Pairwise Interactions

The excitation of the electromagnetic field in the chain of spherical metal nanoparticles by an arbitrary finite source is considered with the account of interactions of all nanoparticles. The contributions of plasmons and waves having the nonexponential spatial field dependence are distinguished. The dispersion of plasmon solutions is determined. The solution of the problem of summation of the diverging sum appearing when the local field is calculated is demonstrated.