The linear-to-elliptical transformation of a 400 nm femtosecond-probe pulse in the birefringent filament in argon of an 800 nm linearly polarized femtosecond-pump pulse is studied numerically and experimentally. The rotation of the probe elliptical polarization is the largest in the high-intensity filament core. With propagation, the rotated radiation diffracts outward by the pump-produced plasma. The transmission of the analyzer crossing the probe's polarization is maximum at the pump-probe angle of 45 degrees and gives equal values for each pair of angles symmetrically situated at both sides of the maximum.
Spatial contraction of high-peak-power femtosecond pulse in air leads to its simultaneous shortening in time domain. Numerical simulations in the slowly evolving wave approximation show that the full width at half maximum duration of the 45 fs 800 nm pulse becomes ∼ 8 fs as soon as the intensity reaches the ionization threshold. At this propagation distance the compressed pulse accumulates maximum of its energy that is ∼ 4% of the initial pulse energy. Higher than the second orders of material dispersion decrease the maximum possible energy achieved in the compressed pulse. Self-compressed pulse after 6 m of propagation in air. Initial fullwidth half-maximum duration 45 fs shrinks down to ∼ 8 fs
We discuss methods and algorithms of high-temperature laser plasma electron diagnostics based on hard x-ray yield and ionic time-of-flight (TOF) spectra measurements in comparison with the results of direct electronic spectrum recording, with the help of the electrostatic spectrometer. The latter shows clearly the two-component nature of the electron population, arising at femtosecond laser plasma interaction. 'Temperatures' of 200 eV and 6 keV for thermal and hot electronic components, correspondingly, were estimated from this measurement. We show that both ionic TOF measurements and doublechannel hard x-ray detection allows the assessment of mean hot electron energy in a single laser shot. The former also provides for estimation of the thermal electron temperature and plasma charge state. Good coincidence between the data obtained from the three methods employed is demonstrated. We also describe how to apply our hard x-ray detection method to the case of relativistic laser plasma interaction, where single shot assessment may become even more essential.
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