On the vibronic theory of resonance Raman scattering

Resonance Raman excitation profiles of totally symmetric vibrational modes are investigated using a model that analytically includes the complete subspace of Franck-Condon active vibrations associated with each intermediate electronic state. This model is used to fit data obtained in resonance with the Soret band of cytochrome c. The excitation profiles are asymmetric and peak distinctively to the blue of the Soret absorption maximum. Large damping factors and/or inhomogeneous site distributions by themselves cannot account for the observed data. The theoretical results imply that the excited state lifetime associated with the Soret band of ferrocytochrome c has a lower limit on the order of 50 fs and that, compared to the ferrous form, the ferric cytochrome has a larger x-y splitting and a shorter lifetime.In constrast to the large multidimensional heme system, we also present the results of a simple model calculation applicable to smaller molecules. A two dimensional subspace is explored, where Raman Franck-Condon (RFC) and Franck-Condon (FC) factors are calculated for different potential energy surface parameters. Under certain conditions the RFC based scattering profiles of one vibration are strongly coupled to the FC based behaviour of the other vibration. Rather complex profiles are then predicted even for the simple two- dimensional case.     

On the quantum theory of superradiance in two-and three-level macroscopic systems

Modified quantum kinetic equations for the superradiance in two-and three-level macroscopic systems that interact with electromagnetic fields are derived based on the method for elimination of the boson variables. It is demonstrated that the theoretical predictions are in good agreement with the experimental data.     

On the theory of lasing at vibronic transitions in impurity crystals

Some aspects of lasing at vibronic transitions in impurity crystals are theoretically studied. The threshold conditions for a vibronic laser are shown to be dependent on the strength of the interaction of optical centers with a local vibration, which forms the vibronic spectrum, and the crystal lattice temperature. The theory can easily be generalized to the spectrum containing a structureless phonon sideband and well agrees with the experimental temperature dependence of the output power of a Mg₂SiO₄:Cr⁴⁺ forsterite laser.     

Generalized Fokker-Planck equation in superradiance theory

An alternative projector technique approach to the Bonifacio-Schwendimann-Haake model of superradiance is presented. A bilinear master equation for the probability distributions of photon number and atomic excitation is derived. In the case of very large numbers of atoms we end up with a generalized Fokker-Planck equation for atoms.     

Exact solution and scaling theory of superradiance

The general scaling theory of transient phenomena near the instability point, which has been proposed by one of the present authors (M.S.), is applied to investigate the fluctuation and relaxation of superradiance near the complete inversion (or instability point). An exact solution for a simple model of superradiance has been obtained to study the relaxation and fluctuation of it near the complete inversion and to confirm the validity of the scaling theory. It is found that this asymptotic evaluation method yields very good results for a large system size Ω. The Ω-expansion method by van Kampen and by Kubo et al. is also discussed in this model in order to clarify the connection of it with the scaling theory.     

New space-time effects in superradiance: Experiment and theory

A new effect has been observed in the superradiance of praseodymium ions in a lanthanum trifluoride matrix: the effect of selecting transverse pumping structures upon the oblique-incidence pumping of superradiant media. A simple explanation for this effect is given. The possible reasons for the stochastization of the oscillatory regime of superradiance, a phenomenon observed upon both the normal and oblique incidence of pumping radiation on a crystal and when the crystal is placed in a resonator with an eigenfrequency close to the frequency of the superradiant transition, are analyzed.     

Scaling theory of fluctuation in superradiance relaxation from the complete inversion

The general scaling theory of transient phenomena near the instability point, which has been proposed by the author, is applied to investigate the fluctuation and relaxation of superradiance from the complete inversion. This study gives a foundation or justification of the treatment of Glauber and Haake.     

On the stability of parameters of molecular models in the parametric method of the theory of vibronic spectra

We have studied the stability of the system of parameters used in the parametric method of the theory of vibronic spectra of polyatomic molecules with respect to whether the initial structural-dynamic model of the ground state of a molecule is formed either by the fragmentary method or by direct quantum-chemical calculation. Modeling of excited states and spectra of the stilbene-h ₁₂ and stilbene-d ₁₂ molecules showed that, although the initial models of the ground states are significantly different, calculated changes in the geometry that occur upon excitation and electronic-vibrational spectra of the models are close and quantitatively agree with experiment. This indicates that the parameters of the method are stable and are applicable for performing predictive calculations of vibronic spectra based on models of the ground states created by different methods. We show that the fragmentary method has a considerable advantage, since models created by this method take into account the continuity of the structure in series of related compounds and calculations can be easily performed for molecules of arbitrarily high complexity. We show that direct quantum-chemical calculations are important in the case of molecules with unknown structural-dynamic models of fragments in the ground states.     

Semiempirical adiabatic theory of the vibronic spectra of multiatomic molecules

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 48, No. 6, pp. 963–967, June, 1988.     

On a solution to the single-mode model of superradiance

A self-similar solution of the diffusion equation for the atomic quasi-probability function discussed by Narducci and Bluemel is derived.     

Charge transfer excitons: dynamic theory of vibronic spectra

The vibronic spectra of charge transfer excitons (CTE) in a molecular one-component or alternatingly ordered two-component chain are treated in the framework of a dynamic approach (neglecting thermal excitations of the intramolecular vibrations). The model introduces two mechanisms of coupling between CTEs and vibrational quanta: (1) shift of the equilibrium positions of the nuclei in the ionized donor or acceptor; (2) change of the vibrational frequency in the ionized molecule. This model allows to generalize the simple CTE Hamiltonian and the vibronic Hamiltonian of Frenkel excitons. The linear optical susceptibility is calculated in the vibronic region (one CTE and one vibrational quantum). The double splitting of vibronics of CTEs was analyzed: (1) the splitting connected with the location of the intramolecular vibration on the donors or on the acceptors; (2) the splitting connected with the symmetry of the vibronic spectra (in the degenerate case). The general structure of the vibronic spectra of CTEs is established. It contains structureless absorption lines, which correspond to two-particle bands (the phonon is excited on a neutral molecule neighboring the donor or the acceptor) and Lorentz-type lines of one-particle states, which correspond to the bound propagation of the CTE and the phonon.     

Stimulated superradiance

If N atoms simultaneously interact with quasiresonant classical and quasiresonant quantized fields, the modes exchange photons. This processes exhibits cooperative properties, i.e., the number of photons in the quantized mode oscillates, and the amplitude of these oscillations is proportional to N ². Zh. éksp. Teor. Fiz. 116, 858–869 (September 1999)     

The Argyres-Kelley approach to the master equation and an extended theory of superradiance

A discussion of the Argyres-Kelley approach to the Master Equation is set up, and applied to the Bonifacio-Schwendimann-Haake model of Superradiance. Some properties of the approach and its limits are discussed, and an extension of the BSH theory of Superradiance is obtained.     

在群论框架下电子三重态与声子耦合的理论研究

本文基于绝热近似和群论导出了电声耦合系统的哈密顿量的一般形式,讨论了电声耦合系统中的电子算符和活跃的声子模式. 应用幺正平移变换和能量最小化方法,进一步计算了正四面体群下T*(e+t₂)杨-泰勒系统中的激发态能量,从对称性的角度分析了T₁电子态的能级分裂以及晶格体系的对称性破缺,得出了对称性的破缺方式和电声耦合系统密切相关的结论. 结果表明:通过群论与对称性分析完全可以定性地解释由于电声耦合所造成的简并电子 关键词： 电声耦合 杨-泰勒畸变 活跃的杨-泰勒声子模式 电声耦合哈密顿量     

On the structure of field at the phase transition to the superradiance state

It is shown that at the phase transition to the superradiance state a nonlinear periodic wave structure of the field may be excited. Amplitude, width and number harmonics in the wave packet are determined by the boundary conditions and temperature.     

Photon echo under superradiance

The dynamics of optical coherence and phase memory in three-level medium in conditions of superradiance pulse emission is considered. In the case of coherent excitation of the upper level in three-level system of lambda configuration it is shown that the superradiance eliminates optical coherence on the adjacent transitions of excitation and superradiance emission and induces optical coherence on the remain transition. This, in turn, makes it possible to observe new effects of photon-echo, simple example of which is described in the present Letter.     

Fluctuation in superradiance

The fluctuation of the intensity of superradiant pulse is calculated by applying a general asymptotic evaluation method of quantal macrovariables to a superradiant master equation. It is shown that the fluctuation of superradiant intensity is proportional to the cube of the number of the relevant atoms. The time-dependence of the proportional coefficient has been evaluated explicitly. It is predicted that there occurs an enhancement of fluctuation of superradiant intensity at an intermediate time. The intensity and fluctuation of higher order are also calculated. General expressions of expansion coefficients of a generating function are also given rigorously.