an apparatus for sampling , analyzing and displaying an electrical signal as disclosed having a good signal - to - noise ratio and high resolution . the apparatus includes a light pulse source for emitting a light pulse toward the electro - optical surface of a photoelectron sampling tube which in turn emits a photoelectron pulse after receiving the light pulse . the emitted photoelectron pulse is then modulated by a signal to be measured and is accelerated to an anode which may comprise a display for displaying the wave form of the electrical signal as a two - dimensional image .