Mode-hopping-free scanning over 2 THz by means of quasi-synchronous tuning

We report mode-hopping-free tuning (MHF) over 2 THz (6 nm) of a Littman-Metcalf-type external-cavity diode laser by means of quasi-synchronous tuning, wherein the pivot point is displaced 65 mm away from the conventional rigorous synchronous rotation center. An experimental method for judging the relative position between actual pivot location and the quasi-synchronous tuning line is developed. An adjustment structure with only one freedom of movement is enough to accurately locate the pivot point, and the precise requirement is relaxed to more than 300 μm for achieving a MHF tuning range of over 1THz in our configuration.