Large enhancement of spontaneous emission rates of InAs quantum dots in GaAs microdisks

We have studied the enhancement of spontaneous emission rates for InAs quantum dots embedded in GaAs microdisks in a time-resolved photoluminescence experiment. Inhomogeneous broadening of the quantum dot energy levels and random spatial distribution of the quantum dots in a microdisk lead to a broad distribution of the spontaneous emission rates. Using a nonnegative least-norm algorithm, we extract the distribution of spontaneous emission rates from the temporal decay of emission intensity. The maximum spontaneous emission enhancement factor exceeds 10.     

The multi-field Schrödinger lattices

Integrable differential-difference analogues of the generalized Schrödinger equations are constructed. A one-to-one correspondence between them and the triple Jordan algebras is established.     

Absorption-induced confinement of lasing modes in diffusive random media

We present a numerical study of lasing modes in diffusive random media with local pumping. The reabsorption of emitted light suppresses the feedback from the unpumped part of the sample and effectively reduces the system size. The lasing modes are dramatically different from the quasi modes of the passive system (without gain or absorption). Even if all the quasi modes of a passive diffusive system are extended across the entire sample, the lasing modes are still confined in the pumped volume with an exponential tail outside it. The reduction of effective system volume by absorption broadens the distribution of decay rates of quasi modes and facilitates the occurrence of discrete lasing peaks.     

Numerical study of light correlations in a random medium close to the Anderson localization threshold

We applied a finite-difference time domain algorithm to the study of field and intensity correlations in random media. Close to the onset of Anderson localization, we observe deviations of the correlation functions, in both shape and magnitude, from those predicted by the diffusion theory. Physical implications of the observed phenomena are discussed.     

Polariton local states in periodic Bragg multiple-quantum-well structures

We study analytically the optical properties of several types of defect in Bragg multiple-quantum-well structures. We show that a single defect leads to two local polariton modes in the photonic bandgap. These modes lead to peculiarities in reflection and transmission spectra. Detailed recommendations for experimental observation of the effects studied here are given.     

Entrainment and stimulated emission of ultrasonic piezoelectric auto-oscillators

Theoretical modeling and laboratory tests are conducted for nonlinear auto-oscillating piezoelectric ultrasonic devices coupled to reverberant elastic bodies. The devices are shown to exhibit behavior familiar from the theory of coupled auto-oscillators. In particular, these spontaneously emitting devices adjust their limit-cycle frequency to the spectrum of the body. It is further shown that the auto-oscillations can be entrained by an applied field; an incident wave at a frequency close to the frequency of the natural limit cycle entrains the oscillator. Special attention is paid to the phase of entrainment. Depending on details, the phase is such that the oscillator can be in a state of stimulated emission: the incident field amplifies the ultrasonic power emitted by the oscillator. These behaviors are essential to eventual design of an ultrasonic system that would consist of a number of such devices all synchronized to their mutual field, a system that would be an analog to a laser. A prototype uaser is constructed.     

On integrable two-dimensional generalizations of nonlinear Schrödinger type equations

New Bäcklund transformations of integrable 2 + 1 dimensional generalisations of nonlinear Schrödinger type equations are found. The corresponding Miura transformations and modified equations are constructed. The Bäcklund transformations being treated as two-dimensional chain equations provide examples of new integrable difference-differential equations.     

Self-optimization of optical confinement in an ultraviolet photonic crystal slab laser

We studied numerically and experimentally the effects of structural disorder on the performance of ultraviolet photonic crystal slab lasers. Optical gain selectively amplifies the high-quality modes of the passive system. For these modes, the in-plane and out-of-plane leakage rates may be automatically balanced in the presence of disorder. The spontaneous optimization of in-plane and out-of-plane confinement of light in a photonic crystal slab may lead to a reduction of the lasing threshold.     

Discrete equation on a square lattice with a nonstandard structure of generalized symmetries

We clarify the integrability nature of a recently found discrete equation on the square lattice with a nonstandard symmetry structure. We find its L-A pair and show that it is also nonstandard. For this discrete equation, we construct the hierarchies of both generalized symmetries and conservation laws. This equation yields two integrable systems of hyperbolic type. The hierarchies of generalized symmetries and conservation laws are also nonstandard compared with known equations in this class.