355 nm diffractive beam shaper: modes and mechanism of failure and its impact on operational lifetime

Abstract

One of the key tasks of a laser systems field service engineer is to determine where and why an optical system is not performing to specification or why it has failed prematurely. On most occasions, the field service engineer is faced with a completely failed optical system and is left to isolate how and where the failure occurred and if the rest of the system was affected, if at all. Failure modes are the manner whereby the failure itself is observed. Generally speaking, an "optical failure mode" describes the way in which the optical failure happens and its impact on an entire optical system. Optical failure modes of diffractive optical beam shapers must be determined according to each components performance standards as identified through its design and testing. Optical performance standards must be quantified if they are to be upheld. Quantifiable performance standards are more precise than qualitative standards, but each have a role in determining overall performance. If an optical designer or engineer is incapable of specifying precisely, the optical / functional performance they want from the diffractive optical beam shaper, then it is difficult, if not near impossible, to make a field service and maintenance engineer responsible for maintaining optical performance or to identify the possible different failure modes and mechanisms. Performance can be a function of the placement of optics due to routine maintenance or general wear and tear, but there needs to be established means of identifying both circumstances. Diffractive optical element failure mechanisms are straightforward; defined simply as the physical, chemical or other processes that led to the failure of the diffractive optical element itself. This paper outlines schematically the various (Highest Ranked) failure modes and mechanisms encountered by a standard industrial diffractive optical beam shaper operating at 355 nm in an industrial environment. Furthermore, an overview of field data including optical lifetime averages, metrological image data of failed optical elements and methods to prevent premature failure will be shared.