High quality ultrafast transmission electron microscopy using resonant microwave cavities.

Ultrashort, low-emittance electron pulses can be created at a high repetition rate by using a TM110 deflection cavity to sweep a continuous beam across an aperture. These pulses can be used for time-resolved electron microscopy with atomic spatial and temporal resolution at relatively large average currents. In order to demonstrate this, a cavity has been inserted in a transmission electron microscope, and picosecond pulses have been created. No significant increase of either emittance or energy spread has been measured for these pulses. At a peak current of 814 ± 2 pA, the root-mean-square transverse normalized emittance of the electron pulses is ɛn,x=(2.7±0.1)·10-12 m rad in the direction parallel to the streak of the cavity, and ɛn,y=(2.5±0.1)·10-12 m rad in the perpendicular direction for pulses with a pulse length of 1.1-1.3 ps. Under the same conditions, the emittance of the continuous beam is ɛn,x=ɛn,y=(2.5±0.1)·10-12 m rad. Furthermore, for both the pulsed and the continuous beam a full width at half maximum energy spread of 0.95 ± 0.05 eV has been measured.