Lorenzo Fini

Accuracy of remote sensing of water temperature by Raman spectroscopy.

We present an experimental study of the Raman spectrum of pure and synthetic seawater with respect to its salinity and temperature dependence. Experiments made in the laboratory with both cw and pulsed excitation yield information on the limits and applicability of the technique in actual experiments in the field. We have also performed an experimental analysis to determine the presence of stimulated Raman scattering and its influence on the temperature dependence of the spectrum.

Laser-induced structure in the continuum of sodium: a weak dressing field measurement

We report an experimental study of a laser-induced resonance in the continuum of sodium, performed by measuring the modified atomic susceptibility. The sensitivity of the set-up has allowed the observation of the induced structure in conditions of relatively weak intensity of the dressing laser field, where the line shape is independent of the field amplitude and the comparison with theory is strict and direct. We have found a good agreement with theoretical predictions and measured the Fano parameter of the resonance.

Observation of a laser-induced structure in the ionization continuum of sodium atoms using photoelectron energy spectroscopy

We report an experimental analysis of a structure induced by a Nd:YAG laser embedding the sodium excited state in the ionization continuum. The induced structure is probed from the ground state via a one-photon ionization. The experiment is performed on an atomic beam apparatus which uses a time-of-flight spectrometer for energy analysing the emitted photoelectrons. The selectivity of this technique provides the best measurement of a laser-induced resonance in the photoionization spectrum reported to date. A good agreement is found between the theory and experimental results.

Multiphoton time-delay spectroscopy using not transform-limited laser pulses

We report on a two-photon resonant three-photon ionisation experiment performed on atomic barium with a sequence of two identical not transform-limited laser pulses in the weak field regime. We show that our results, obtained by a multimode nanosecond laser source, can be reproduced theoretically by using much shorter transform-limited pulses with the same spectral bandwidth.

Effect of incoherent processes on laser-induced continuum structures

We present an experimental investigation of the effect of incoherent processes on a laser-induced continuum structure. Accurate measurements of the resonance profile, performed in a weak-field regime by the polarization technique, have allowed a quantitative study of the effect of a finite laser bandwidth and of the collisional self-broadening on the line shape.

Electron angular distributions in non-resonant three-photon ionization of xenon

We present the measurement of electron angular distributions in the three-photon non-resonant ionization of xenon (with = 266 nm) above the P1/2 and P3/2 thresholds. Our results for the P3/2 threshold are compatible with previous measurements. The sensitivity of our set-up allowed us to measure the angular distribution of the P1/2 threshold and to resolve unobserved features of P3/2 continua. A measurement of the ionization branching ratio has also been performed. The experimental results show discrepancies with theoretical calculations reported in the literature.

Resonance fluorescence of a two-level atom driven by a short laser pulse: extension to the off-resonance excitation

The resonance fluorescence of a two-level atom interacting with a laser pulse is studied, following the short-pulse approximation. The authors demonstrate that an explicit expression of the energy spectrum in terms of atomic-state amplitudes holds also for an off-resonance excitation. Some analytically solvable cases are studied in detail, showing that the main spectral properties of the fluorescence emitted under adiabatic and non-adiabatic pulsed excitation can be easily described. For the first time the continuous dependence of the fluorescence spectrum on laser detuning is reported for a smooth pulse.

High contrast measurement of a laser-induced structure in the ionization continuum of sodium by photoelectron spectrometry

An experimental analysis of the structure induced by a strong laser field in the continuum of ionization of the sodium atom is reported. The experiment is performed on an atomic beam provided with a time-of-flight spectrometer, for an energy analysis of the photoelectrons. A substantial improvement in the evidence of the resonance has been obtained thanks to the selectivity of the detection system.

Control of the final state photoionization products by laser-induced continuum structure

We report on the observation of the modification of the final status products in a photoionization of the Xe atom through the coherent process of laser-induced continuum structure (LICS). The photoionization decay of the Xe ground state into the two electronic continua, corresponding to the two fine structure levels of the ground state of the Xe ion, is varied by embedding a bound state into the two continua through a laser field (dressing laser). The dressed continua, probed from the atomic ground state through three-photon absorption, exhibit different induced structures. The experiment is performed on an atomic beam apparatus which uses a time-of-flight spectrometer for energy analyzing the emitted photoelectrons. The modified final state amplitudes are controlled by the wavelength of the dressing laser. No significant modification of the 2P3/2 continuum has been observed, in the limit of the detection efficiency. The effect is characterized by a window resonance in the slow electron continuum as the d...

Experimental studies of quantum control in atoms

We present selected examples of recent experimental results in coherent quantum control of processes and products of laser atom interactions. These include control of ionization and autoionization rates, of light induced atomic structure, ionization branching ratios and frequency up-conversion. Quantum interference of atomic transitions, induced by a bichromatic electromagnetic field, is underlying all the results of this work. Since the quantum interference is induced by the field, its parameters govern control of products and processes. Thus control is demonstrated through the wavelength, intensity and phase of the field.