G. G. Grigoryan

The near infrared (0.8-2.6 mu m) absorption spectrum of a dense sodium vapor and possible mechanisms of the spectrum formation

The absorption coefficient of a dense sodium vapor (N0 ∼ 1017–1018 cm− 3) in the near infrared spectral range (0.8–2.6 µm) was measured in a homogeneously heated isolated cell. In the range of parameters studied, the sample exhibits significant absorption. Neither the observed spectral features nor the measured absorption coefficients can be explained using the existing notions of the possible absorption mechanisms (absorption due to a forbidden intercombination transition, collision-induced processes, the trimer vapor component, and many-particle effects) and the available data.

Spiky structure of coherent emission from optically thick media

The spiky structure of the spontaneous emission from praseodymium ions in the LaF3 lattice on the 3P0-3H6 transition under coherent pulsed excitation of the adjacent 3H4-3P0 transition has been studied experimentally and theoretically. The experimental results are in good agreement with the theoretical conclusions based on analysis of the emission dynamics of an excited ensemble of three-level systems in the mean field approximation. The generation of a spiky structure is interpreted as the emission of a cnoidal wave pulse. The recorded random pattern of time intervals between the spikes reflects the sensitivity of the cnoidal wave period to fluctuations in the system. The developed theory has been found to be related to models of deterministic chaotic dynamics.

Superradiant emission of LaF3:Pr3+ in resonator

Experimental data concerning superradiant emission from the LaF3 medium doped with impurity praseodymium ions are presented in the cases of a free medium and when the medium is placed into an optical resonator. The spike structure of superradiance is registered and studied. When the medium is placed inside a cavity, a new channel of energy removal by superradiance related to the cavity mode appears; the old noncavity channels are preserved. The duration of superradiance in the cavity channel is decreased, and regular modulation arises. These peculiarities of superradiance induced by the presence of an optical resonator are explained.

Temporal structure of superradiance of praseodymium ions in the LaF3 matrix: theory and experiment

Experimental data and theoretical model describing stochastic pulsations within oscillatory mode of superradiant emission from the LaF3 medium doped with impurity praseodymium ions are presented. The model deals with three-level system with close upper levels and reflects our experimental data on fluorescence of praseodymium ions. The mean-field approximation is used to develop the superradiance theory. In determined case basic equations of the developed model are reduced to well known Lorenz equations of deterministic chaotic dynamics.

Dynamics of superradiant medium in resonator

Experimental data and theoretical model concerning superradiant emission from the LaF3 medium doped with impurity praseodymium ions are presented in cases of free medium and when the medium is placed into resonator. The spiky structure of superradiance is registered and studied. When the medium is placed inside a cavity, a new channel of energy removal by superradiance related to the cavity mode appears; the old noncavity channels are preserved. The duration of superradiance in each channel is decreased and the modulation arises. These peculiarities of superradiance induced by the presence of resonator are explained on the basis of the developed mean-field theory.

The features of coherent stimulated emission of Pr3+ doped into LaF3 matrix

The paper presents the experimental results on temporal characteristics of coherent stimulated emission on the 3PO-3H6 transition of Pr3+ doped into the LaF3 matrix while turning the pumping frequency in the vicinity of 3H4-3PO transition. The stimulated emission was generated in the modes both with and without an external resonator. It was found that the emission duration could be up to 2 μs and consisted of train of spikes. Simultaneously the fluorescence emission was observed on the 3PO-3H4, 3H5j, 3H6, 3F2 transitions Pr3+, which also had a complicated temporal form.

Temporal evolution of coherent stimulated emission in the three-level system LaF3:Pr3+

The paper reports the experimental results on the temporal characteristics of coherent stimulated emission on the 3P0-3H6 transition of Pr3+ ion dopped into the LaF3 matrix while tuning of pumping frequency in the vicinity of the 3H4-3P0 transition. The generation pulse duration was found to be about 10 ns, and it was delayed by 3-4 ns relative to the beginning of the pumping pulse at the exact resonance. It was observed that as the detuning increased, the shape of the coherent stimulated emission pulse changed and its delay increased up to 10ns. A theoretical interpretation of the experimental results observed is proposed.

Effect of the pump absorption on generation of infrared stimulated electronic Raman scattering in alkali-metal vapors

The main properties of infrared stimulated electronic Raman scattering (SERS) at the 62S1/2-72S1/2, 3/2 transitions in cesium atoms are studied theoretically and experimentally as functions of the atomic concentration, which was varied from 1011 to 1016 cm−3. It is found that the efficiency of generation of Stokes radiation strongly depends on one-photon absorption of the pump radiation tuned near frequencies of the 62S1/2-72P1/2, 3/2 transitions. By using the equation for the density matrix, which describes the evolution of a three-level system, the theory of resonance excitation of IR radiation upon one-photon absorption at an adjacent transition is developed. The theory describes well the main features of IR SERS in alkali-metal vapors.