Experimental Observation of A 100-Femtosecond Single Electron Bunch in Photocathode Linac with Longitudinal Emittance Compensation Technique

The realization of a 100fs electron pulse is important for the studies of ultrafast physical/chemical phenoena with a pump-probe method. We have developed a photocathode linear accelerator (linac) to generate such electron pulse with a magnetic bunch compressor. The nonlinear effect of the magnetic fields in the pulse compression was compensated carefully by optimizing the magnetic fields and the booster linac RF phase. A 98 fs electron bunch in rms with electron charge of 0.17 nC was observed experimentally by using a femtosecond streak camera. The beam energy was 32 MeV, and the normalized teraservers emittance was lower than 3.8 mm-mrad. The dependences of the bunch length, the relative energy spread and the emittance on the electron charge were also measured.