E. Sali

Ramsey spectroscopy of bound atomic states with extreme-ultraviolet laser harmonics

We report the experimental measurement of Ramsey interference fringes in the single-photon excitation to a high-lying bound state of atomic argon by pairs of phase-locked, time-delayed, extreme UV high-order-harmonic pulses at 87 nm. High-visibility Ramsey fringes are observed for delays larger than 100 ps, thus demonstrating a potential resolving power >10(5) at this wavelength.

Enhancement of harmonic generation by Fresnel-lensing effects

We present experimental results of enhanced second- and third-harmonic generation efficiency from Fresnel-lensing effects. We obtained enhancement by a factor of 6 in the third-harmonic yield by simply limiting the laser beam with an iris. Higher enhancement factors (up to 16) were obtained with a Fresnel zone plate. The experimental findings are in good agreement with the results of a simple theoretical analysis.

A Titanium-doped-sapphire laser source with tunable frequency, single-mode emission, and adjustable pulse duration

We present a laser source with several desirable characteristics, such as tunable wavelength in the near infrared, single-longitudinal-mode emission and variable pulse temporal duration in the nanosecond regime. The laser is based on an injection-seeded Titanium-doped-sapphire ring cavity. Our experiments show how the pulse duration can be varied in a controllable fashion either by changing the cavity length or by changing the pump energy. We present a theoretical model which successfully reproduces the experimental results by treating the operation of this type of laser as a gain-switching technique. As far as the stabilization of the laser cavity, we also present a novel solution involving the use of an avalanche photodiode.

Controllable optical delay of wideband laser pulses by means of coherent effects

We report the first experimental observation of controllable temporal delay of wideband laser pulses (input spectral bandwidth of 3.3 GHz) using electromagnetically induced transparency. We obtain this result with limited temporal distortion of our pulses and excellent values of the delay-bandwidth product. Our experimental results are in agreement with a theoretical analysis.

Perspectives of Ramsey schemes based on high-order harmonics for high-resolution XUV spectroscopy

We present an experimental and theoretical investigation of Ramsey-type interference fringes using high-order harmonic generation. The ninth harmonic (λ ≃ 88 nm) of a femtosecond Ti:sapphire laser was used to excite a pair of autoionizing states of krypton. The outcome of the ionization process, detected by an ion-mass spectrometer, shows the characteristic quantum interference pattern. The behavior of the fringe contrast was interpreted on the basis of a simple analytical model, which reproduced well the experimental results without any free parameter. Finally, we also present a proposal for a similar experiment to be performed on high-lying bound state of atomic argon, with the aim of achieving even higher resolving power.

Laser-pulse compression by coherent control in a Doppler-broadened medium: Analytical and numerical studies

We have studied the temporal compression of laser pulses occurring in a scheme based on the coherent control peculiarities of electromagnetically induced transparency. This work extends earlier model studies, including the effect of Doppler broadening in a real hot medium. For definiteness and consistency of the atomic parameters employed, we have treated a scheme in argon. In this way, we establish a realistic model that enables us to predict quantitatively the performance of laser pulse compression experiments.

Control of slow and fast light by incoherent interactions in atomic schemes

We present recent theoretical and experimental results concerning both retardation and acceleration of light pulses in schemes involving a second ‘control’ laser field but that do not involve any coherent preparation of the atomic medium.

All-optical control of the group velocity, central frequency and spectral bandwidth of a laser pulse

We present recent results on different schemes (involving both coherent and incoherent interactions) that allow all-optical control of several properties of a large-spectral-bandwidth (up to 3.3 GHz) laser pulse propagating in an atomic medium.

Ramsey-type spectroscopy in the XUV spectral region

We report an experimental and theoretical investigation of Ramsey‐type spectroscopy with high‐order harmonic generation applied to autoionizing states of Krypton. The ionization yield, detected by an ion‐mass spectrometer, shows the characteristic quantum interference pattern. The behaviour of the fringe contrast was interpreted on the basis of a simple analytic model, which reproduces the experimental data without any free parameter.

Temporal Compression of Laser Pulses by Coherent Control

We present our most recent theoretical results on a temporal compression technique based on electromagnetically‐induced transparency. An experiment aimed to provide a first proof‐of‐principle demonstration of the process is also described.