M. Nisoli

Millijoule-level phase-stabilized few-optical-cycle infrared parametric source.

Ultrabroadband self-phase-stabilized near-IR pulses have been generated by difference-frequency generation of a filament broadened supercontinuum followed by two-stage optical parametric amplification. Pulses with energy up to 1.2 mJ and duration down to 17 fs are demonstrated. These characteristics make such a source suited as a driver for high-order harmonic generation and isolated attosecond pulse production.

Efficient continuum generation exceeding 200 eV by intense ultrashort two-color driver

A temporal gating on the high-order harmonic emission process is achieved using an intense 20 fs, 1.45 microm pulse (IR) in combination with an intense 13 fs, 800 nm pulse [visible (VIS)]. Exploiting this two-color gating scheme, a coherent continuous emission extending up to 160 eV using Ar gas and 200 eV using Ne gas is efficiently generated. The IR pulse contributes to significantly extending the harmonic emission to higher photon energies, whereas the VIS pulse improves the conversion efficiency of the process. These results indicate the possibility to produce bright attosecond pulses approaching the soft X spectral region.

Characterization of a high-energy self-phase-stabilized near-infrared parametric source

We present a broadband self-phase-stabilized near-IR source based on difference frequency generation (DFG) of a filament broadened supercontinuum followed by a two-stage optical parametric amplifier. We demonstrate pulses with energy up to 1.2 mJ and duration down to 17 fs. We theoretically study the process of DFG and investigate the carrier-envelope phase (CEP) dependence on the driving pulse parameters. We find that robust CEP stability is possible even with fluctuations in the phase and intensity of the DFG seed pulse. These characteristics make this parametric source suitable as a driver for high-order harmonic generation and isolated attosecond pulse production.

Few-optical-cycle laser pulses: from high peak power to frequency tunability

Recent advances in ultrafast laser technology have led to the generation of light pulses comprising few optical cycles employing different compression techniques. In particular, two techniques have been developed, which allow addressing the issues of high peak power or frequency tunability in a wide spectral range, namely: the hollow-fiber compression technique and the optical parametric amplification. The paper analyzes the general scheme of pulse compression and reports on the most interesting results obtained using the above-mentioned techniques. The combination of spectral broadening in a gas-filled hollow fiber with ultrabroad-band dispersion control, has led to the generation of pulses with duration of /spl sim/5 fs with peak powers up to 0.11 TW. Using optical parametric amplifiers with different configurations sub-15-fs laser pulses have been generated tunable in the visible and in the near-infrared.

Elemental sensitivity in soft x-ray imaging with a laser-plasma source and a color center detector

Elemental sensitivity in soft x-ray imaging of thin foils with known thickness is observed using an ultrafast laser-plasma source and a LiF crystal as detector. Measurements are well reproduced by a simple theoretical model. This technique can be exploited for high spatial resolution, wide field of view imaging in the soft x-ray region, and it is suitable for the characterization of thin objects with thicknesses ranging from hundreds down to tens of nanometers.

Generation of high-energy self-phase-stabilized pulses by difference-frequency generation followed by optical parametric amplification

We produce ultrabroadband self-phase-stabilized near-IR pulses by a novel approach where a seed pulse, obtained by difference-frequency generation of a hollow-fiber broadened supercontinuum, is amplified by a two-stage optical parametric amplifier. Energies up to 20 microJ with a pulse spectrum extending from 1.2 to 1.6 microm are demonstrated, and a route for substantial energy scaling is indicated.

Femtosecond relaxation of photoexcitations in a solution of a poly(para-phenylene)-type ladder polymer

Abstract The primary photoexcitations of a poly(para-phenylene)-type ladder polymer in toluene solution are studied by a time-resolved pump-and-probe technique. Upon exciting the sample with 120 fs pulses a strong stimulated emission is found with a decay time of 190 ps. The stimulated emission centered in the blue/green region at 490 nm shows no spectral overlap with the observed photoinduced absorption, which makes the m-LPPP a promising candidate as the active medium for laser applications.

Temporal characterization of a time-compensated monochromator for high-efficiency selection of extreme-ultraviolet pulses generated by high-order harmonics

Ultrafast extreme-ultraviolet pulses are spectrally selected by a time-delay-compensated grating monochromator. The intrinsic very short duration of the pulses is obtained by exploiting the high-order harmonic generation process. The temporal characterization of the harmonic pulses is obtained using a cross-correlation method: pulses as short as 8 fs are measured at the output of the monochromator in the case of the 23rd harmonic. This value is in agreement with the expected duration of such pulses, indicating that the influence of the monochromator is negligible. The photon flux has been measured with a calibrated photodiode, pointing out the good efficiency of the monochromator, derived by the exploitation for the two gratings of the conical diffraction mounting.

Poly(3-decylthiophene) as χ(3) active material in waveguides

Abstract Four-layer waveguided structures exhibiting acceptable losses have been realized using spin-coated samples of poly(3-alkylthiophene) from FeCl 3 . Particular attention has been devoted to the molecular-weight range and crystallite dimensions to minimize the scattering losses and to increase the birefringence. Time-resolved bleaching decay measurements gave strong off-resonance signals (λ range 1300–1500 nm), indicating interesting χ (3) values.

Phase-Contrast Imaging of Nanostructures by Soft X Rays from a Femtosecond-Laser Plasma

The possibility of phase-contrast imaging of nanostructures has been analyzed with the use of a femtosecond-laser plasma as a spatially coherent soft x-ray source and a LiF crystal as an x-ray detector having both the submicron spatial resolution in a wide field of view and a high contrast. It is demonstrated that the spatial coherence length of radiation in the wavelength range 1–13 nm at a distance of 30 cm from the femtosecond-laser plasma source is ≃1.5 μm. The achieved spatial coherence of the source is sufficient to obtain high-quality phase-contrast x-ray images of foils with various chemical compositions and a thickness of ≃100 nm.