E. S. Andrianov

Dipole response of spaser on an external optical wave

We find the conditions upon the amplitude and frequency of an external electromagnetic field at which the dipole moment of a Bergman-Stockman spaser oscillates in antiphase with the field. For these values of the amplitude and frequency the loss in metal nanoparticles is exactly compensated by the gain. This shows that spasers may be used as inclusions in designing lossless metamaterials.

Forced synchronization of spaser by an external optical wave

We demonstrate that when the frequency of the external field differs from the lasing 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 values of the external field amplitude and the frequency detuning (the Arnold tongue) for which the spaser synchronizes with the external wave.

Stationary behavior of a chain of interacting spasers

We show that depending on the values of the coupling constants, two different scenarios for the stationary behavior of a chain of interacting spasers may be realized: (1) all the spasers are synchronized and oscillate with a unique phase and (2) a nonlinear autowave travels along the chain. In the latter scenario, the traveling wave is harmonic, unlike excitations in other known nonlinear systems. Due to the nonlinear nature of the system, any initial distribution of spaser states evolves into one of these steady states.

Rabi oscillations in spasers during nonradiative plasmon excitation

In the approach to the stationary regime, a spaser exhibits complicated and highly nonlinear dynamics with anharmonic oscillations.1 We demonstrate that these oscillations are due to Rabi oscillations of the quantum dot in the field of the nanoparticle. We show that the oscillations may or may not arise dependent on the initial conditions.

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.

Spaser operation below threshold: autonomous vs. driven spasers

At the plasmon resonance, high Joule losses in a metal nanoparticle of a spaser result in its low Q-factor. Due to the latter, to achieve the spasing regime, in which the number of coherent plasmons exceeds the number of incoherent plasmons, unsustainably high pump rates may be required. We show that under the condition of loss compensation by a spaser driven by an external optical wave, the number of coherent plasmons increases dramatically, and the quantum noise is suppressed. Since the compensation of losses of the driving wave may occur even near the spasing threshold, the number of coherent plasmons may exceed the number of spontaneously excited plasmons at achievable pump rates.

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).

Superradiance of non-Dicke states

In 1954, Dicke predicted that a system of quantum emitters confined to a subwavelength volume would produce a superradiant burst. For such a burst to occur, the emitters must be in the special Dicke state with zero dipole moment. We show that a superradiant burst may also arise for non-Dicke initial states with a nonzero dipole moment. Both for Dicke and non-Dicke initial states, superradiance arises due to a decrease in the dispersion of the quantum phase of the emitter state. For non-Dicke states, the quantum phase is related to the phase of long-period envelopes which modulate the oscillations of the dipole moments. A decrease in the dispersion of the quantum phase causes a decrease in the dispersion of envelope phases that results in constructive interference of the envelopes and the superradiant burst.

Parametric instability of optical non-Hermitian systems near the exceptional point

In contrast to Hermitian systems, the modes of non-Hermitian systems are generally nonorthogonal. As a result, the power of the system signal depends not only on the mode amplitudes but also on the phase shift between them. In this work, we show that it is possible to increase the mode amplitudes without increasing the power of the signal. Moreover, we demonstrate that when the system is at the exceptional point, any infinitesimally small change in the system parameters increases the mode amplitudes. As a result, the system becomes unstable with respect to such perturbation. We show such instability by using the example of two coupled waveguides in which loss prevails over gain and all modes are decaying. This phenomenon enables compensation for losses in dissipative systems and opens a wide range of applications in optics, plasmonics, and optoelectronics, in which loss is an inevitable problem and plays a crucial role.

Magnetically Controlled Vertically Emitting Laser with Anisotropic Pumping

A vertically emitting Faraday laser that is pumped by quantum wires or strongly anisotropic quantum dots is considered. As distinct from a similar laser on a quantum well or isotropic quantum dots, such a laser is extremely sensitive to external magnetic field (up to switching-off by magnetic field). This circumstance can be used for development of a rapidly tunable source of coherent radiation.