CTR Bunch Length Measurement of Monoenergetic and Maxwellian Electron Beams from Laser Plasma Cathode

Recently, several plasma cathodes at universities and institutes can generate a monoenergetic electron beam. LBL measured the bunch length by the CTR (Coherent Transition Radiation) interferometer to determine it as about 50 fs (FWHM). We are trying to carry out a single-shot measurement of the bunch length by a infrared polychromator. As the first step forward it, we measured the CTR spectra emitted at a 300microm-thick Ti foil by the electron beams from our plasma cathode. The laser parameters are 12 TW, 50fs, 3x1019W/cm2. He gas-jet is used and the electron density is 6x1019cm-3. By using the liquid He bolometer and several optical low-pass filter, we measured the spectra of the CTR. We can clearly classify the difference of the spectrum and bunch length for the monoenergetic and Maxwellian beams. The numerical analysis of the bunch elongation due to the energy spread confirms the experimental results. The bunch length of the monoenergetic beam is less than 100 fs at FWHM with about 10 pC per bunch, which is consistent with the PIC simulation. The next single-shot measurement with the FIR (Far-Ingfra-Red) polychomator and application to a pump-and-probe experiment for radiation chemsitry are also discussed.