High damage threshold and highly reliable broad-band mid-ir coatings for high power fluoride fiber laser

Abstract

This invention provides a process or fabrication method of forming broadband anti-reflective (AR) coating over the mid-IR fluoride fiber for high power laser applications in mid-IR wavelength range. The AR coating consists of multiple-pair Lithium fluoride (LiF) and AlO, and was deposited by electron beam physical vapor deposition with an iron assistant source at low temperature (<60° C.). A thin encapsulation layer of AlOwas applied over the AR coating by atomic layer deposition technology. The measurements show the coating has a reflectivity of <1-1.5% in the range of 1.5-5.5 μm. The laser induced damage threshold (LIDT) test shows the damage threshold is greater than 8.9 MW/cm2 with no sign of any damage on the coating exposed to atmosphere. The durability and environmental tests of the AR coating with PVD coated encapsulation layer show good humidity resistance in open air and no degradation of film quality and optical performance are observed.