Raw images of the electron beam obtained on the LANEX screen for a plasma density of . Panels (a) and (b) The pulse was at the best compression (duration and intensity ). (c) Pulse duration , intensity . (d) Pulse duration , intensity .
Electron energy distribution obtained from the raw images of Fig. 1. The full curve and the dotted curve represent spectra for pulse durations of ; the dashed curve was obtained with a duration of . The horizontal bars represent the spectrometer resolution for different electron energies.
Schematics illustrating spectral broadening and self-compression of a laser pulse in a plasma wave.
(a) Schematics of the experimental setup which was used for the measurement of laser pulse shortening. (b) Picture of the compact single shot autocorrelator.
Transmitted laser spectra for different plasma densities.
(a) Lineouts of autocorrelation traces. Dashed line: autocorrelation for a zero plasma density, full line: autocorrelation for . The inset represents a possible pulse shape. (b) Same as (a) but the full line was obtained for .
(a) Transmission of the infrared interferential filter which was used in order to isolate the wavelength range of interest. (b) Transmission of the whole optical system, including reflections on glass wedges, transmission through several silicon filters, germanium filters, and the interferential filter.
Dependence of infrared signal with experimental parameters. The empty circles represent the signal detected with the HgCdTe detector; the full diamonds represent the charge for electrons with energies greater than . Each dot is an average of 3–5 shots. The empty circles have two error bars: the left ones come from the rf noise; the middle ones come from statistical fluctuations. (a) Variation of IR signal when the plasma density is changed. (b) Variation of IR signal when the gas jet position with respect to the laser focus is varied.
Comparison between the signal level modeled using incoherent transition radiation (dashed line) and the measurement (full circle). The horizontal error bar indicates the wavelength range of the detection. The vertical error bar represents shot to shot fluctuations over 5 shots.
(a) Two possible shapes for the electron bunch: a Gaussian bunch (full line) and a Lorentzian bunch (dashed line). Both shapes reproduce the measured signal when the coherent transition radiation spectrum is calculated. (b) Comparison between the measured IR signal and coherent transition radiation models for different electron bunch shapes. (c) Same as above with a Gaussian bunch (full line) and two Gaussian bunches separated by (dashed line). (d) The transition radiation spectrum emitted for the Gaussian (full) and double Gaussian pulse (dashed).
Geometry of the radiation emitted by an electron when exiting the radiator. The electron exits the radiator along vector , at angle and azimuthal angle . The radiation is collected in solid angle along vector , at angle with the radiator plane.
Table showing the dependence of electron bunch rise time and duration at FWHM for different pulse shapes. “Double Gaussian” refers to two Gaussian electron bunches separated by .
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