A detachable high-speed optoelectronic sampling head for use with an electron multiplier includes a housing having an evacuated chamber with a pair of transparent windows. Light to be detected is directed to the first window to a photoemissive strip spaced from a ground plane. The photoemissive strip comprises a microstrip, and the housing has high frequency feedthrough means for applying sampling potentials between said photoemissive strip and ground plane. A phosphor layer is provided on the other window in the chamber, and photoelectrons emitted from the photoemissive strip are directed through the ground plane to the phosphor layer.