Vladimir V. Likhanskii

Phase locking in multichannel laser systems

It is well known way to increase the radiation power by combining beams from many lasers. However, the great increase in the intensity on the target may be obtained only if all beams are mutually coherent. The problem of making radiation of multichannel (multi-element) laser coherent was widely discussed. Several review articles were published recently [1-3] . The idea of coherent combining of a large number of phase locked beams is used in several concepts of super-high-power laser system: for chemical HF/DF lasers [4], for free electron lasers [5), for semiconducter lasers [6). The following methods to phase locking for laser array were considered: 1. frequency and phase locking of laser array to the radiation of master oscillator (MO) by adaptive optics method [7]; 2. the scheme master oscillator and power amplifier array [8; 3. phase locking of slave laser array to the injection signal from MO [9); 4. optical coupling between resonators (channels) of laser array [10]. Method of adaptive optics is attractive because it may have universal applications. However it needs design and production of many detectors, modulators, electrical serve loops and so on. Finally, it would be very complex system. The schemes 2 and 3 are at very initial stage of development. It was shown experimentally that the HF multiline radiation after the power amplifier (PA) may be coherently combined on a target with the radiation from MO [8] . The questions are leaving open of oscillator isolation and of choosing parameters of PA and MO to achieve high power and efficiency simultaneously. The amplifier array concept was not tested experimentally. There is a successful attempt at coherent combining of MO radiation with the radiation of injection locked Nd-YAG laser [11] . However, the transfer of this method to the array of injection locked lasers seems to be highly problematic due to tight tolerances for resonator length detunings. The concept of optically coupled laser array evolved very fast. So, this paper will be devoted to new results and ideas that made a progress in the concept of optically coupled lasers after the overviews [1-3] . These results relate to the problem of phase locking for two lasers and for the array of N lasers and concern the spectrum of collective modes and their stability. The dynamics of optically coupled lasers due to the resonator lengths detunings will be considered, too.

Dynamic modes of operation of a laser with periodic pumping

The paper reports on results of studies on dynamic modes of operation of a laser with periodic pumping. The bifurcation diagram in a two-dimensional space of managing parameters is constructed. The obtained characteristics allow for prediction of modes of synchronous operation of two optically coupled lasers.

Instabilities and waves of coherence in 1D diode laser arrays

Theory and numerical simulation of the stability and dynamic behavior of a diode laser array with nearest-neighbor coupling are discussed. The coupling coefficient is assumed to be the complex number. The linewidth enhancement factor plays the crucial role in instability development and wave field dynamics. In dependence on the values of the amplitude and phase of the coupling coefficient and of the linewidth enhancement factor the stable phase- locked operation, waves of the laser field distribution, regular oscillations, and chaotic dynamics can be observed. For different above threshold conditions as phase as amplitude chaos could be realized. The steady state and dynamic operation for a linear and ring arrays are compared. The linear stability analysis of nonlinear array modes for ring configuration is developed. Along with the wave field amplitudes the discrete Fourier spectrum was calculated. Results of simulations demonstrate that the active medium inertia plays an important role in the evolution of wave fields in the array, particularly when the characteristic variation time is on the order of the period of the relaxation oscillation for a sole laser. In the near-to-resonance conditions the increase in the intensity modulation depth took place, and the cooperative nature of oscillations became more pronounced.

Regular and chaotic pulsations of radiation intensity in a CO2 laser with modulated parameters

The experimental and theoretical investigations of radiation dynamic in a system of two optically-coupled C02-lasers and in a periodically - pumped COlaser are carried out. In a optically-coupled lasers on the edge of theirs locke- band and in a periodically-pumped laser near threshold the transition of lasers to the chaotic generation through subsequent period-doubling bifurcations are experimentally revealed. A good agreement between experimental and theoretical results was obtained.

Stability Of Phase-Locked Lasing In A Two Coupled Unstable Resonator System

We describe the performance of two lasers with homogeneously saturated gain, coupled through central hole in a common mirror of symmetric unstable resonators. New iterative procedure is proposed based on combining the Fox-Li and Prony methods. The suggested procedure allowed us to calculate several resonator modes and find a stable phase-locked operating region for various sizes of coupling hole and small signal gain values. Far field patterns from combined lasers are computed for various operating regimes.