An autocorrelator to measure pulse width of an incident laser divides the incident laser to a reference beam and a controlled beam. Two rotating parallel mirrors are used as an optical delay component for the controlled beam. The axis of rotation of the rotating parallel mirrors and the incident beam on the parallel mirrors are on the same horizontal plane. There is a small angle δ between them. The scan range can be easily adjustable by changing this angle δ. Using this arrangement, real-time and range adjustable autocorrelator is realized.