Stefano Cavalieri

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.

Temperature-tunable random lasing: numerical calculations and experiments

We report numerical studies on temperature-tunable, multiple-scattering media with gain. We describe Monte Carlo simulations that model the behavior of such a system through a three-dimensional random walk of light in a temperature-dependent disordered medium with amplification. We compare the results of our model with previous experimental results on a disordered dielectric for which the scattering strength could be tuned by changing the external temperature. The agreement between the numerical and experimental results enables us to predict the spectral features of the emission from the tunable random laser under various conditions. Results obtained from new experimental data are consistent with the predictions of the simulations.

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.

Optimal control of type I second-harmonic generation with ultrashort laser pulses

We apply the optimal control technique to the topic of type I second-harmonic generation with ultrashort laser pulses. We design temporally tailored fundamental-frequency laser pulses that generate, in the regime of pump depletion, temporally symmetric second-harmonic optical pulses.

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.

Resonant interaction of smooth laser pulses with two-level atoms

The authors have studied the fluorescence spectrum of a two-level atom interacting with a resonant smooth laser pulse. Assuming a filter width larger than the Fourier width of the pulse, an approximate analytic closed form for the power spectrum valid for any pulse shape is obtained. In these conditions the power spectrum exhibits a time-developing three-peak structure, while the energy spectrum presents a single line, unless the pulse is near rectangular. Theoretical energy spectra are in qualitative agreement with measurements of the resonance fluorescence emitted by strontium atoms irradiated by short laser pulses.

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.