  Ultrashort, low-emittance electron pulses can be created at a high repetition
rate by using a TM$_{110}$ 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 $814\pm2$ pA, the root-mean-square transverse normalized
emittance of the electron pulses is $\varepsilon_{n,x}=(2.7\pm0.1)\cdot
10^{-12}$ m rad in the direction parallel to the streak of the cavity, and
$\varepsilon_{n,y}=(2.5\pm0.1)\cdot 10^{-12}$ 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
$\varepsilon_{n,x}=\varepsilon_{n,y}=(2.5\pm0.1)\cdot 10^{-12}$ m rad.
Furthermore, for both the pulsed and the continuous beam a full width at half
maximum energy spread of $0.95\pm0.05$ eV has been measured.
