Diagnostics of subpicosecond electron pulse by the fluctuation method

We performed the diagnostics of subpicosecond and picosecond electron pulses by the fluctuation method. The method is based on the observation of the shot-drivennoise fluctuations of incoherent radiation and was proposed by M. Zolotorev et al. (1998). In our case, Cherenkov radiation and optical transition radiation emitted from the electron pulse were detected by the photodiode for the time-domain measurement and by the spectrometer for the frequency-domain measurement. Results by these measurements were compared with the pulse duration independently taken by the femtosecond streak camera. Another feature of our diagnostics is the large transverse beam size. The effect of the transverse beam size upon the fluctuation was discussed with the aid of the numerical simulations