23 research outputs found
Enhancement of bichromatic high-harmonic generation with a high-frequency field
Using a high-frequency field superposed to a linearly polarized bichromatic
laser field composed by a wave with frequency and a wave with
frequency , we show it is possible to enhance the intensity of a
group of high harmonics in orders of magnitude. These harmonics have
frequencies about 30% higher than the monochromatic-cutoff frequency, and,
within the three-step-model framework, correspond to a set of electron
trajectories for which tunneling ionization is strongly suppressed. Particular
features in the observed enhancement suggest that the high-frequency field
provides an additional mechanism for the electron to reach the continuum. This
interpretation is supported by a time-frequency analysis of the harmonic yield.
The additional high frequency field permits the control of this group of
harmonics leaving all other sets of harmonics practically unchanged, which is
an advantage over schemes involving only bichromatic fields.Comment: 6 pages RevTex, 5 figures (ps files), Changes in text, figures,
references and equations include
Demonstration of aluminum
Targets consisting of 25\un{nm}
\chem{Al} layers buried in solid
carbon at depths of up to 400\un{nm} have been irradiated with
frequency doubled \chem{Ti}:sapphire laser pulses of 150\un{fs}
duration at an intensity of a few 1017
\un{W/cm^2}. The
analysis of the emitted \chem{Al}
K-shell spectra yields
densities close to that of solid \chem{Al} and temperatures around
500\un{eV}. By using the cold \chem{Si}
line for
wavelength calibration, the presence of a red dense-plasma line
shift for several K-shell resonance and associated satellite
lines is clearly demonstrated
Demonstration of aluminum K-shell line shifts in isochorically heated targets driven by ultrashort laser pulses
Targets consisting of 25 nm Al layers buried in solid carbon at depths of up to 400 nm have been irradiated with frequency doubled Ti:sapphire laser pulses of 150 fs duration at an intensity of a few 1017 W/cm2. The analysis of the emitted Al K-shell spectra yields densities close to that of solid Al and temperatures around 500 eV. By using the cold Si Kα line for wavelength calibration, the presence of a red dense- plasma line shift for several K-shell resonance and associated satellite lines is clearly demonstrated
K-shell spectra from hot dense aluminum layers buried in carbon and heated by ultrashort laser pulses
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X-ray line emissions from tamped thin aluminum targets driven by subpicosecond-duration laser pulses
Role of the plasma scale length in the harmonic generation from solid targets
We have investigated the generation of high harmonics from the interaction of 150 fsec, 790 nm, and 395 nm laser pulses with solid targets. Experiments are presented that demonstrate a strong dependence of the conversion efficiency on the temporal pulse shape and the resulting density scale length (L/λ) of the preformed plasma. The highest conversion efficiencies are achieved for short density scale lengths (L/λ ≤ 0.4), which result from high contrast ratio pulse interactions