Intense Resonant Field Research Articles

Non-linear optical spectroscopy of single molecules in solids at low temperatures

We report on pump-probe experiments on single molecules in a solid matrix, with strong laser fields and on a new host-guest system, dibenzanthanthrene in a naphthalene crystal. Besides strong light-shifts of the molecular lines, we observe the hyper-Raman resonance and for strong pump and probe beams, we also observe subharmonic resonances due to a ‘kicked pendulum’ motion of the Bloch vector. The experimental results are in very good agreement with calculations based on Bloch's equations, demonstrating their validity for single molecules in solids under intense resonant fields.

Pump–probe spectroscopy and photophysical properties of single di-benzanthanthrene molecules in a naphthalene crystal

We report on a new crystalline host–guest system for single molecule spectroscopy; dibenzanthanthrene (DBATT) in a naphthalene crystal. As compared to DBATT in an n-hexadecane Shpol’skii matrix (a combination studied earlier), this system is shifted to the red (618.7 nm), has a lower triplet yield and shorter triplet lifetimes. Thanks to the narrow lines of this system (20 MHz), to its high photostability and to the absence of spectral diffusion, even in strained crystals, we could measure line shapes and widths with great accuracy. As an illustration of the potential of this new system for quantum optical experiments, we present pump–probe experiments with strong laser fields. The experiments are in very good agreement with calculations based on Bloch’s equations, demonstrating the validity of these equations for single molecules in solids under intense resonant fields.

Fluctuational transitions between stable states of a nonlinear oscillator driven by random resonant force.

Fluctuations of a nonlinear oscillator driven by an intense resonant field with fluctuating phase are considered in the region of bistability. The general expression for the probability of a fluctuational transition between stable states is found to logarithmic accuracy. In the weak-damping limit the probabilities are obtained in the explicit form including both the argument of the exponential and the preexponential factor. A simple general method of determining the latter for underdamped systems is suggested. The probability of an escape from a metastable state near the bifurcation point where this state disappears is analyzed. The low-frequency susceptibility of the oscillator is shown to have a peculiar structure in the region of parameters where the stationary populations of the stable states are of the same order of magnitude. The stochastic modulation of the phase of an oscillator due to coupling to a bath is considered and its consequences are compared to those of randomness of the phase of a driving field.

Cooperative effects in a system of strongly driven three-level atoms.

Cooperative effects in a system of three-level atoms in cascade configuration interacting with intense resonant fields are investigated. Analytical expressions for atomic populations in the excited levels, fluorescence intensities, and normalized intensity correlations are presented. The intensity correlations are used to test the violation of the Cauchy-Schwarz inequalities. The analytical results predict in the cooperative limit N\ensuremath{\rightarrow}\ensuremath{\infty}, a discontinuous behavior of all atomic observables with respect to a parameter related to the field amplitudes and the atomic decay coefficients. This discontinuous behavior is analogous to a typical nonequilibrium first-order phase transition.

Heitler-Ma solution of the schrödinger equation for an atom in an intense resonant field

We show how the formalism developed by Heitler and Ma can be used to study the time development of a system consisting of an atom interacting with an intense resonant electromagnetic field.