METHOD TO STABILIZE A WAVELENGTH OF A TUNABLE LASER DEVICE, TUNABLE LASER DEVICE, AND POSITION MEASUREMENT SYSTEM PROVIDED WITH THE TUNABLE LASER DEVICE

摘要

The technology relates to controlling the wavelength of a laser output of a tunable laser device. The tunable laser device may be used, for instance, to monitor displacement of equipment in a lithographic apparatus. For example, the tunable laser device and the disclosed methods of control liny the wavelength thereof may be applied in projection systems fur optical lithography systems, A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may. for example, project a pattern (also often referred to as "design layout" or "design") of a patterning device (e.g.. a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g.. a wafer).