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P Villoresi

Publications and source records attributed to P Villoresi.

11 recordsLinked to original sources
PubMed2006

Isolated single-cycle attosecond pulses.

We generated single-cycle isolated attosecond pulses around approximately 36 electron volts using phase-stabilized 5-femtosecond driving pulses with a modulated polarization state. Using a complete temporal characterization technique, we demonstrated the compression of the generated pulses for as low as 130 attoseconds, corresponding to less than 1.2 optical cycles. Numerical simulations of the generation process show that the carrier-envelope phase of the attosecond pulses is stable. The availability of single-cycle isolated attosecond pulses opens the way to a new regime in ultrafast physics, in which the strong-field electron dynamics in atoms and molecules is driven by the electric field of the attosecond pulses rather than by their intensity profile.

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PubMed2005

Measurement of harmonic phase differences by interference of attosecond light pulses.

By using a self-referencing technique, we have experimentally measured the influence of the carrier-envelope phase of femtosecond light pulses on the phase of the electric field of the radiation produced by high-order harmonic generation. We show that, in particular experimental conditions, the temporal evolution of the electric field of the attosecond pulses, is directly controlled by the carrier-envelope phase of the driving pulses.

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PubMed2004

Observation of carrier-envelope phase phenomena in the multi-optical-cycle regime.

So far the role of the carrier-envelope phase of a light pulse has been clearly experimentally evidenced only in the sub-6-fs temporal regime. Here we show, both experimentally and theoretically, the influence of the carrier-envelope phase of a multi-optical-cycle light pulse on high-order harmonic generation. For the first time, we demonstrate that the short and long electron quantum paths contributing to harmonic generation are influenced in a different way by the pulse carrier-envelope phase.

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PubMed2003

Above-threshold ionization at the few-cycle limit.

Photoelectron spectra measured for rare-gas atoms ionized with intense few-cycle laser pulses are presented. Several aspects of the few-cycle regime are discussed. In particular, the persistence of the plateaulike structure of spectra for high electron energies is shown. In contrast, a resonancelike feature at similar electron energies is suppressed as compared with longer laser pulses. Differences in the behavior of different species and implications for the electron-ion scattering cross section are pointed out.

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PubMed2002

High-brightness high-order harmonic generation by truncated bessel beams in the sub-10-fs regime.

Low-divergence, high-brightness harmonic emission has been generated by using a fundamental beam with a truncated Bessel intensity profile. Such a beam is directly obtained by using the hollow-fiber compression technique, which indeed allows one to optimize both temporal and spatial characteristics of the high-order harmonic generation process. This is particularly important for the applications of radiation, where extreme temporal resolution and high brightness are required.

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PubMed2001

Experimental evidence for detuning induced pattern selection in nonlinear optics.

We give quantitative experimental evidence of the influence of cavity detuning in determining the pattern selection in a one-dimensional large Fresnel number optical oscillator. The issues of the selection of the transverse mode close to threshold and the value of the pump parameter at threshold are addressed. Competition between right and left traveling waves, resulting in a winner takes all dynamics, is also reported. Experimental results are in quantitative agreement with the theoretical predictions formulated for a broad class of systems comparable to the one here considered.

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PubMed2001

Absolute-phase phenomena in photoionization with few-cycle laser pulses.

Currently, the shortest laser pulses that can be generated in the visible spectrum consist of fewer than two optical cycles (measured at the full-width at half-maximum of the pulse's envelope). The time variation of the electric field in such a pulse depends on the phase of the carrier frequency with respect to the envelope-the absolute phase. Because intense laser-matter interactions generally depend on the electric field of the pulse, the absolute phase is important for a number of nonlinear processes. But clear evidence of absolute-phase effects has yet to be detected experimentally, largely because of the difficulty of stabilizing the absolute phase in powerful laser pulses. Here we use a technique that does not require phase stabilization to demonstrate experimentally the influence of the absolute phase of a short laser pulse on the emission of photoelectrons. Atoms are ionized by a short laser pulse, and the photoelectrons are recorded with two opposing detectors in a plane perpendicular to the laser beam. We detect an anticorrelation in the shot-to-shot analysis of the electron yield.

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PubMed2000

Spectral features and modeling of high-order harmonics generated by sub-10-fs pulses

Harmonic radiation generated in a neon gas jet by sub-10-fs laser pulses was investigated both experimentally and theoretically. The spectral profile of the harmonics with respect to the order, their intensity and relative spectral shifts were measured as a function of the position of the gas jet. The results point out spectral features typical of the quasi-single-cycle excitation regime. A nonadiabatic three-dimensional numerical model was developed, which provides harmonic spectra in remarkable agreement with the experiments.

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