  Time-resolved transport of ballistic electrons in a two-dimensional electron
gas has been measured with a resolution of less than 5ps. This was accomplished
by using picosecond electrical pulses to launch electrons from the emitter of a
transverse magnetic focusing structure and optoelectronically sampling the
collector voltage. Both plasma resonances and the ballistic transport signal
are clearly resolved. The transit time appears to be somewhat longer than
expected from simple Fermi velocity considerations.
