Optical Manifestations of Energy and Phase Relaxation in Vibronic Systems

Vladimir A. Shcheglov

Boris D. Fainberg, Vladimir N. Nazarov

Changes in the modulus and phase of a slowly varying envelope of an ultrashort pulse are calculated for the case of propagation across a saturable absorber. Vibronic relaxation of the optical transition in the absorber is allowed for. A study is made of the dependences of the duration of a pulse transmitted by a nonlinear absorber on the vibrational relaxation time of dye molecules and on the detuning of the carrier frequency of a pulse relative to the maximum of the equilibrium absorption spectrum. It is shown that a chirp appears even in the absence of such detuning provided the energy of lf quanta of optically active vibrations is comparable with the thermal excitation energy. This chirp originates from partial completion of the vibrational relaxation process during a pulse, so that absorption and refraction occur in a system which is not in a vibrational equilibrium.

K.‐E. Süsse, W. Vogel, D.‐G. Welsch

The problem of resonant interaction between an electromagnetic radiation field and a vibronic system, such as a molecule or a localized electronphonon system, is considered. The vibronic coupling is assumed to result from displaced and distorted potential energy surfaces for the vibrational motion in the electronic quantum states involved in the resonant interaction with the radiation field. Furthermore, the vibrational energy relaxation is taken into account without assumptions about Markovian-type relaxation. In order to study correlation properties of higher than second order in the electric field strength of the light emitted a method of calculation of the expectation value of an arbitrary product combination of effective time evolution operators of the vibronic system is developed. The calculations are performed by utilizing Feynman's disentangling and operator ordering techniques and yield closed solutions in the low-temperature limit. The theory is used for studying the intensity and the normally ordered intensity correlation function of the resonance fluorescence light from a two-atom molecule excited by a relatively weak laser field, which undergoes phase fluctuations. It is shown that the vibronic coupling can give rise to an anticorrelation effect which is substantially stronger than in the case of resonance fluorescence from an atom. For the case of small vibrational damping a general formula which directly connects the asymptotic long-time behaviour of the normalized intensity correlation function with the vibrational relaxation in the molecule is deduced. It should be convenient for the determination of very small vibrational decay rates.

Takashi Kushida, Shuichi Kinoshita

N. G. Preobrazhenskii, S. V. Senina

Andrei V. Ivanov, Evgeniy Perlin

Abstract Vibronic coupling effects usually manifest themselves in molecules and crystals rather than in unbound atoms. We theoretically demonstrate the existence of vibronic states in a moving two-level atom exposed to a strong electromagnetic (EM) wave. In this case, the Rabi oscillations of the electron density give rise to periodic displacements of the atomic nucleus with the Rabi frequency. The periodic displacements mix the Stark split electron levels and lead to the establishment of a channel for energy transfer in the atomic system. Such a channel paves the way for fast control of the kinetic energy of a free atom with the use of the parameters of an EM wave. Thus, the system kinetic energy can be decreased or increased if the detuning between the laser pulse frequency and the optical transition is positive or negative, respectively. For actual values of the detuning, the pulse duration should be an order of magnitude longer than the lifetime of the excited atomic level in order to complete the energy transfer process.