H. S. Brandi

Inert gas atom–molecule collisions in a laser field: Vibrational excitations in homopolar molecular ions

We investigate the effect of an electromagnetic field in the vibrational excitations of diatomic molecules, considering its collisions with noble gas atoms. Considering colinear collisions we obtain an expression for the vibrational transition amplitudes, and we apply the formalism to the specific collision He+H+2 in CO2 laser field, in the high energy approximation. The general behavior of the multiphoton transition amplitude as a function of the relevant parameters of the system is discussed for the 0→1 vibrational excitation.

Effects of a spatially inhomogeneous laser field in non-linear absorption in solids☆

Abstract We investigate the influence of a spatially inhomogeneous laser field on the multiphoton absorption processes occurring in direct-gap semiconductors. We adopt a “non-perturbative” approach to treat the single-mode spatially homogeneous case using a parabolic band model to describe the solid. We show that corrections due to inhomogeneity may change the results in a significant way and thus have to be considered when comparing the calculated multiphoton absorption coefficients with the experimental data.

Laser multimode effects in non-linear absorption in solids

Abstract We show that a more realistic description than the single mode laser field may introduce modifications in the results concerning multiphoton absorption in solids more significant than those introduced by correcting for non-parabolicity, excitonic effects and so on. A multimode description corresponding to pulsed lasers is considered as an example.

Resonance enhanced two-photon absorption in solids☆

Abstract We apply the dressed bands approach to investigate the role of intermediate states in two-photon absorption in solids. Calculations show that the transition probability is sensitive to intermediate state resonances and is also strongly affected by the laser field intensity. Qualitative comparison is made with experiments.

Random soliton distribution in trans-polyacetylene

Abstract We investigate the electronic density of states (DOS) and the localization properties of trans-polyacetylene with a random distribution of neutral narrow soliton-type defects. The problem is treated within the Renormalized Virtual Crystal Method with triplet decimation, which preserves the soliton contribution to the DOS. The localization of the state at the Fermi energy is calculated as a function of soliton concentration cs, and our results indicate that a significative increase of the hopping conductivity may occur for cs ∼ 5 - 10%.