Abstract: Autocorrelation traces of laser pulses of short duration are produced by a method and apparatus that uses a rotating glass block to vary the path length on a time scale rapid enough to display the traces on a synchronized oscilloscope. Both paths of a split input beam of a laser pulse pass through the glass block. Rotation of the glass block changes the relative time of travel for light pulses along the two paths. The paths of the two beam arms pass through the block from different directions at a relative angle chosen so that the relative travel time difference is nearly linearly related to the angular position of the block during its rotation.Autocorrelation with rapid scanning through rotation of the block enables measurement of repetitive laser light pulses of very short duration, down to the order of one picosecond.