Roberto Buffa

Laser-induced collisional energy transfer

Abstract A review of the status of theoretical and experimental work on Laser-Induced Collisional Energy Transfer (LICET) is presented. The process involves two dissimilar atoms, one of which is excited, colliding in the presence of a laser field. If the radiation field is properly tuned to an interatomic resonance, the initially excited system undergoes a transition to its ground state, while its partner gains both the excitation energy and that of a photon. The transfer cannot occur unless both collisional and radiative interactions are present. The line shape of the excitation spectrum, markedly asymmetric, is closedly related to the interaction dynamics. Details of theories applicable to low intensities, as well as their high-field counterparts are discussed, as are the predictions of spectral shapes and comparison with measurements. The treatment is extended to include studies of magnetic-state and electronic-state coherences, allowing an additional insight into the nature of the process. Representative experimental investigations are surveyed, including a detailed description of experimental arrangements specifically designed for high-accuracy spectral measurements. Finally, it is shown how a wider approach to the LICET process, by considering it as a radiative transition of a transient molecule, can be promising for an improved understanding of the problem.

Simple and efficient H2 Raman conversion of a XeCl laser with a variable numerical aperture coupling geometry

Abstract A simple combination of a lens-based unstable resonator and an inverted telescope coupling geometry working in a XeCl laser pumped H 2 Raman cell are presented. Raman spectrum optimization is achieved by varying the pump beam numerical aperture. 70% pump depletion and energy conversion efficiencies as high as 66% and 7.8% have been obtained for S 1 , S 2 and S 3 respectively.

Optimal control of population transfer through the continuum

This paper describes an approach to the study of selective excitation through continuum intermediate states which provides the optimal temporal shapes of the laser parameters inducing the maximum population transfer achievable from a real atomic system. As an example, the results obtained when the approach is applied to the specific case of atomic hydrogen are also presented.

Analysis and performance of a nitrogen pumped dye laser optimized for narrowband operation

Abstract The analysis and the operating characteristics of a nitrogen pumped dye laser using four prisms as a beam expander are reported. Three configurations with different expansion values M p and incidence angles on the grating θ 0 , corresponding to a constant total magnification M p /cosθ 0 , have been compared.

Laser-Induced Collisional Energy Transfer: High-Accuracy Measurement of the Spectral Line Shape in Weak-Field Regime

In this paper we report the measurement of the spectral line shape for the laser-induced collisional energy transfer reaction between europium and strontium atoms. Cross-sections were measured in a frequency range of 70 cm–1. Comparison with numerical results obtained by Monte Carlo simulation shows good agreement over the full line shape.

Two-color above-threshold ionization: extension to multiple continua

We present a discussion of the two-color above-threshold ionization process, performed with the aim of studying strong-field continuum–continuum transitions. We extend the approach of Rzazewski [ J. Opt. Soc. Am. B7, 481 ( 1990)] to obtain analytically solvable equations for the multiple continuum model analyzed by Deng Eberly [ J. Opt. Soc. Am. B2, 486 ( 1985)]. Some comments on the effect of continuum–continuum transitions on the line shape of a laser-induced continuum structure are also made.

Effect of a dressing radiation field on the laser-induced collisional energy-transfer line shape.

We describe a new scheme suitable for the study of strong-field effects on the laser-induced collisional energytransfer process. The use of two independently tuned radiation fields, to induce the interatomic transition and to modify the energy levels, is found to give rise to a splitting of the excitation spectrum peak, similar to the Autler-Townes doublet. Owing to the resonant coupling, an observable splitting of a few inverse centimeters can be induced by a dressing laser intensity of the order of 10 MW/cm(2).

Laser-induced resonances in ionizing radiative collisions

Laser-induced resonances in ionizing radiative collisions are investigated. Different pathways to the continuum, induced by laser-assisted collisions, give rise to quantum interferences in the ionization cross section. The process can be viewed as a laser-induced continuum structure of transient molecules formed during atomic collisions.

Resonance fluorescence of a three-level atom driven by delayed laser pulses

A study of the resonance fluorescence emitted by a three-level atom driven by delayed laser pulses is presented with the main aim of investigating the effect of the pulse order on the fluorescence spectrum. The use of a short-pulse approximation, introducing a significant simplification in the problem, allows one to provide an explicit expression for the spectrum. Analytical results, obtained in the framework of the adiabatic interaction, are presented and compared with numerical calculations. As an example, an analytically solvable particular case is also presented.

High-Resolution Lineshape Study of a LICET Process in the Far-Wing

An experimental study of laser-induced collisional energy transfer between europium and strontium atoms is reported. The analysis of the lineshape shows evidence that the cross-section does not follow a simple power law in the quasistatic wing. The experimental results are in agreement with a new theoretical model predicting that this laser-induced excitation cannot be characterised by a universal profile.