E. Benedetti

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.

Intense femtosecond extreme ultraviolet pulses by using a time-delay-compensated monochromator

Extreme-ultraviolet pulses, produced by high-order harmonic generation, have been spectrally selected by a time-delay-compensated grating monochromator. Temporal characterization of the harmonic pulses has been obtained using cross-correlation method: pulses as short as 8 fs, with high photon flux, have been measured at the output of the monochromator.

High-energy, few-optical-cycle pulses at 1.5 µm with passive carrier-envelope phase stabilization

We report on a source of ultrabroadband self-phase-stabilized near-IR pulses by difference-frequency generation of a hollow-fiber broadened supercontinuum followed by two-stage optical parametric amplification. We demonstrate energies up to 200 microJ with 15 fs pulse width, making this source suited as a driver for attosecond pulse generation.

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.

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.

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.

Frequency chirp of long electron quantum paths in high-order harmonic generation.

We report on the first experimental measurement of the spectral broadening of the harmonic emission associated with only the long electron quantum paths as a function of the driving pulse intensity. For such measurements we have estimated the chirp coefficient associated with the long quantum paths, within the strong-field approximation. This coefficient describes how the harmonic phase depends on the intensity of the driving laser field. The dependence of the chirp coefficient on the driving pulse intensity and on the harmonic order, which strongly influence the characteristics of the harmonic radiation, has been experimentally investigated. The experimental values turn out to be in excellent agreement with the results of numerical simulations based on the use of the nonadiabatic saddle-point method.

Measurement of Isolated Attosecond Pulses in the Few-Cycle Regime

We present the generation of isolated attosecond pulses using phase-stabilized 5-fs pulses with time dependent ellipticity. Using a complete temporal characterization technique, we demonstrate compression of the pulses down to 130 as (<1.2 optical cycles).

High energy self-phase-stabilized pulses tunable in the near-IR by difference frequency generation and optical parametric amplification

We generate self-phase-stabilized pulses by difference-frequency generation of a hollow-fibre broadened supercontinuum followed by two-stage optical parametric amplification. This system allows the production of broadband pulses widely tuneable in the near-IR wavelength region. Energies up to 0.2 mJ with 15 fs pulse width are demonstrated. These characteristics make this source suitable as a driver for attosecond pulse generation.