Abstract: A rotationally tunable time delay line device for providing a continually adjustable time delay between two orthogonally polarized laser pulses is described. The device is comprised of one or more rotational delay crystals, each made of a flat uniaxially birefringent crystal with a special orientation of its internal optical axis. The time delay generated between the two orthogonally polarized laser pulses that travel through the rotationally tunable delay line can be continually adjusted by rotating the constituent rotational delay crystals around their surface normals. An application is demonstrated in detail where the rotationally tunable time delay line device is used to form an optical autocorrelator for measuring femtosecond or picosecond duration laser pulses.