A new method of diagnostics of hot electrons from a
laser-produced plasma is experimentally demonstrated.
Titanium-sapphire laser pulses (1\un{J}/130\un{fs}) irradiate
copper foils backed by a dielectric. The energy distribution and
direction of the hot electrons generated is determined by
recording visible Čerenkov radiation with spatial resolution.
The results demonstrate a change in the electron generation
mechanism at relativistic intensities