A novel proton imaging technique was applied which allows a continuous temporal record of electric fields within a time window of several nanoseconds. This proton streak deflectometry was used to investigate transient electric fields of intense (~ 10
^17 W/cm^2) laser irradiated foils. We found out that these fields with an absolute peak of up to 10^8 V/m extend over millimeter lateral extension and decay at nanosecond duration. Hence, they last much longer than the (~ ps) laser excitation, and extend much beyond the laser irradiation focus.
