Transitions in two-level systems at diffusion modulated isotropic interactions

E. Duman

Anatoly I. Burshtein, Anatoly A. Zharikov, S. I. Temkin

The response of a TLS to waves, phase- and frequency-modulated by a purely Markovian process, is calculated rigorously. The spectrum of luminescence characterised by two rates of phase relaxation Gamma 1 and Gamma 2 , rather than one, as in the case of phase diffusion ( Gamma 2 =4 Gamma 1 ), is found. Saturation of TLS and its absorption of light at arbitrary correlation between successive values of its randomly and suddenly varying frequency are determined. The probability of light absorption at any strength of its interaction with TLS and at any rate of frequency modulation is found for uncorrelated frequency change.

S. A. Fedotov

Игорь Сергеевич Осадько

A dynamic theory of two-photon correlators for a single impurity center developed recently by the author [I. S. Osad’ko, Zh. Éksp. Teor. Fiz. 113 , 1606 (1998) [JETP 86 , 875 (1998)] has been generalized to the case in which the center interacts with nonequilibrium two-level systems (TLSs) in polymers and glasses. Quantum tunneling transitions in TLS manifest themselves as random jumps of a spectral line of an impurity center. These jumps can be either spontaneous or light-induced. Interaction between the impurity center and many nonequilibrium TLSs, which exist in polymers, results in a time dependence of the optical dephasing rate 1/ T 2 of an impurity molecule, i.e., in spectral diffusion. This paper describes how the jumps of the spectral line manifest themselves in the two-photon correlator, which can be measured in experiments.

B. Jaskorzyńska, Evgeny V. Vanin, Sten Helmfrid

Gain-saturation gratings, induced by the interaction between the active medium and standing waves in laser cavities, influence the performance of lasers. The modulation depth of the grating is reduced by diffusion of the excitation energy in most host materials, but gain saturation has been modeled only in the limit of strong or weak diffusion. We present an analytical solution of the diffusion equation for two-level systems at an arbitrary diffusion rate. It is shown that for many rare-earth dopants the migration process is not well described by either the weak- or the strong-diffusion approximation.

Declan Mulhall