The recent experiments on a pulsed superfluorescence and prospects of a CW superradiant lasing in various active media, especially semiconductor heterostructures, [1] attract much attention to new coherent dynamical effects in such lasers. These effects take place in the case of very dense active medium and low-Q cavities when a photon (cavity) lifetime is much shorter than a polarization (optical dipole) lifetime of an active center. Here, on the basis of numerical modeling of the Maxwell-Bloch equations, we describe the steady and dynamic spontaneous symmetry breaking of the structure of the field, polarization and population inversion of an active medium with almost homogeneously broadened spectral line placed into a symmetric low-Q combined distributed feedback (DFB) Fabry-Perot cavity.

We propose an asymmetric electron–hole model of an injection semiconductor quantum-dot laser, which correctly allows for relaxation at transitions between the electron and hole levels. Steady-state solutions of the proposed model, conditions for the simultaneous operation at transitions between the ground and first excited state levels, and relaxation oscillations in the two-wave lasing regime are studied. It is shown that the model can be simplified when the relaxation between hole levels is much faster than the relaxation between electron levels.

Generation of a second giant pulse in a longitudinal mode neighbouring to the longitudinal mode possessing minimal losses is theoretically and experimentally studied in actively Q-switched lasers. A mathematical model is suggested for explaining the giant pulse generation in a laser with multiple longitudinal modes. The model makes allowance for not only a standing, but also a running wave for each cavity mode. Results of numerical simulation and data of experiments with a Nd : YLF laser explain the effect of second giant pulse generation in a neighbouring longitudinal mode. After a giant pulse in the mode with minimal losses is generated, the threshold for the neighbouring longitudinal mode is still exceeded due to the effect of burning holes in the population inversion spatial distribution.

We analyze the electron-hole asymmetry model of a semiconductor quantum dot laser [1] at different relaxation rates of the transitions between electron and hole levels. It is shown that the model can be simplified when the relaxation between hole levels is much faster than the relaxation between electron levels.

We study relaxation oscillations in a semiconductor quantum dot laser using the electron-hole asymmetry model [1]. Two relaxation oscillation frequencies are found in the regime of simultaneous lasing at the ground and excited states. Low-frequency relaxation oscillations are antiphase oscillations at some laser parameters.

A novel model of a semiconductor laser with optical feedback is presented, generalizing Lang-Kobayashi equations to the case of incoherent feedback. The equations are supplemented by a stochastic variable which models random phase difference between the field inside laser cavity and the feedback field. It is shown that for weak-to-moderate feedback the transition from coherent to incoherent feedback leads to replacement of dynamical chaos by almost stationary lasing with slightly fluctuating intensity. Nevertheless, incoherent feedback can lead to chaotic oscillations, but at considerably larger feedback levels.

Simultaneous two-wave lasing was obtained in microchip end-pumped Nd : YAG lasers at the wavelengths of 1061.5 and 1064.17 nm at room temperature. Laser wave intensities were studied as functions of crystal temperature and pump power. The ranges of parameters were determined in which the two-wave lasing occurs and the reasons for such lasing were established. A model is suggested, which adequately describes the experimental results obtained.

It is shown that photonic band-gap (PBG) structures have great potential for the development of widely tunable continues wave and/or mode-locked ultrashort-pulse all-solid-stale lasers in UV and optical ranges. The basic idea is to decrease the laser threshold via inhibition of radiative decay of an upper laser level by embedding an active medium into spatial structure having PBG at the frequency of laser transition. This technique provides favorable conditions for coherent suppression of the excited state absorption crucial for short-wavelength solid-state lasing. It also resolves the laser gain dilemma, providing combination of high emission cross-section and large population inversion. Different designs of 2D and 3D photonic crystal laser are proposed.

A new model of a multi-longitudinal-mode semiconductor laser with weak optical feedback is proposed. This model generalizes the well-known Tang-Statz-deMars equations, which are derived from the first principles and adequately describe solid-state lasers to a semiconductor active medium. Steady states of the model and the spectrum of relaxation oscillations are found, and the laser dynamics in the chaotic regime of low-frequency fluctuations of intensity is investigated. It is established that the dynamic properties of the proposed model depend mainly on the carrier diffusion, which controls mode-mode coupling in the active medium via spread of gratings of spatial inversion. The results obtained are compared with the predictions of previous semiphenomenological models and the scope of applicability of these models is determined.

A chaos-based communication scheme allowing simultaneous bidirectional message transmission (Opt. Lett. 32, 403, 2007) is investigated numerically. Incoherent feedback and coupling case is analyzed, which is expected in real long-distance optical communication systems. It is shown that identical synchronization of chaotic laser waveforms and bidirectional message transmission are possible as in the coherent coupling case. However, the chaotic regime at incoherent feedback and coupling is quite different. It is regular destabilized relaxation oscillations with the chaotic envelope. Such dynamics leads to restriction of the transmitting signal bit rate by a portion of relaxation oscillations frequency.

A novel multilongitudinal mode model of a semiconductor laser is presented. The model takes into account four-wave mixing of the longitudinal modes and is based on the correct procedure of simultaneous expansion of the population inversion in time and space series. It is shown that the model has antiphase regimes similar to those observed in experiment. Such behavior exists in a narrow range of the carrier diffusion coefficient, which allows us to estimate the value of this parameter.

A new method is proposed for estimating the control parameters of single-mode semiconductor optical-feedback lasers from experimentally measured time series of the laser intensity. The procedure is based on a statistical analysis of specially selected points of the time series and on the phenomenon of chaotic synchronization of unidirectionally coupled lasers with coinciding parameters.

Experimental study of low-frequency dynamics of an intracavity frequency-doubled Nd:YAG laser demonstrates the influence of the interaction of orthogonally polarized modes, participating in frequency doubling (type II phase matching), on the stability of the laser output. At a sufficiently low pump rate and low conversion efficiency, the laser shows stable operation with a low noise level at the frequencies of relaxation oscillations. At a high pump power and/or a high conversion efficiency, the laser emission becomes unstable as a result of Hopf bifurcation at the frequencies of relaxation oscillations that are responsible for the anti-phase polarization dynamics of the laser.

The role of spontaneous emission noise and gain line profile in the dynamics of a multimode semiconductor laser with weak-to-moderate optical feedback is studied. Two models of such a laser are compared. If the gain profile is flat and in the absence of noise, model A predicts that all modal intensities are in phase, and model B predicts antiphase dynamics of the modal intensities. Noise induces out-of-phase solutions in model A and hardly affects model B. Weakly curved gain profile determines the number of lasing modes but otherwise has little effect on the laser dynamics in both models.

We analyze the experiment of A. Uchida et al. (2001) reporting on the synchronization of multimode semiconductor lasers coupled unidirectionally through one of the transmitter modes. We show that only the coupled modes are synchronized and that the dynamical regimes of the two lasers are different, though leading to similar power spectra.

We analyze unidirectionally coupled semiconductor lasers in the feedback/injection scheme to determine their synchronization performance. As the mismatch between the two lasers increases, there is a transition from complete synchronization for identical lasers to time lag synchronization which is only partial. This corresponds to a continuous change of the global minimum that becomes a relative minimum of the synchronization error function and vice versa.

We analyse the two longitudinal mode threshold of a solid-state Fabry-Perot laser with a spatially nonuniform pump for two configurations: an end-pumped laser and a laser with a partially filled cavity. The threshold is derived in a consistent way. We prove that inhomogeneous pumping or partial filling of the cavity hardly modify the two-mode threshold.

The interaction of man and nature is considered in terms of classical ecology, which is becoming a synthetic systemic science based on a set of other sciences. The divisions of modern human ecology that deal with different organizational levels of ecological systems have been developed to different degrees. Attention is given to the necessity of discrediting the mechanistic concept of opposition between man and nature and taking into account the specific ecological functions of man related to group adaptation (culture), as well as the global role of all living organisms in the maintenance of environmental conditions on Earth.

When the laser medium only partially fills the cavity of a multimode solid-state laser, there are significant changes in the spectral profile of the emission, the intensity fluctuation power spectra, and modulation transfer functions in comparison with lasers which have media that entirely fill the cavity. These effects are computed according to several approximate models for the multimode interactions and compared with experimental measurements. Symmetries and asymmetries in the multimode optical spectrum have corresponding features in the relaxation oscillation spectra. Changes in the laser cavity detuning and laser excitation lead to relatively abrupt changes in some variables (modal intensities, low-frequency relaxation oscillations) while the total intensity and largest relaxation oscillation frequency vary as they would for a single-mode laser.

The influence of longitudinal pump nonuniformity on the behaviour of a multimode standing wave solid-state laser is studied. It is found that this nonuniformity leads to changes in both the optical spectrum and in the spectrum of relaxation oscillations in comparison with a uniformly pumped laser. Results obtained for two laser models, the global rate equation model and the TSD+ model as its simplified version, are compared. It allows us to verify the validity of the TSD+ model and define the scope of its application.