Laser-induced damage studies on step-index multimode fibers

Conference · Tue Oct 22 20:00:00 EDT 1991 · Proceedings, Laser-Induced Damage in Optical Materials: 1991

DOI:https://doi.org/10.1117/12.60104· OSTI ID:10119867

Setchell, Robert E. ^[1]; Klingsporn, Paul E. ^[2]

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1. Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
2. Allied-Signal Inc., Kansas City, MO (United States)

A previous investigation of laser-induced damage mechanisms and corresponding thresholds in step-index, multimode fibers was motivated by an interest in optical systems for firing explosives. In the initial study, the output from a compact, multimode Nd/YAG laser was coupled into fiber cores of pure fused silica. End-face polishing steps were varied between successive fiber lots to produce improved finishes, and each fiber was subjected to a sequence of progressively increasing energy densities up to a value of more than 80 J/cm². Essentially all of the tested fibers experienced a 'laser conditioning' process at the front fiber face, in which a visible plasma was generated for one or more laser shots. Rather than produce progressive damage at the front surface, however, this process would eventually cease and leave the surface with improved damage resistance. Once past this conditioning process, the majority of fibers damaged at the rear end face. Other modes of damage were observed either at locations of fixturing stresses or at a location of high static tensile stress resulting from bends introduced to the fiber. Although the previous results were encouraging in terms of achieving useful damage thresholds, a number of areas for further study were indicated. In the present study, a similar experimental procedure was used to address these areas. The relative permanence of front-surface laser conditioning was examined by re-testing fibers that had experienced this process at least a year previously. End-face mechanical polishing was again examined by testing fibers prepared using a refined polishing schedule. Attempts to use a single fixture to hold an entire lot of fibers throughout end-face polishing and damage testing met with mixed results, with fiber positions subjected to fixturing stresses likely sites for initial damage. In an effort to prepare fiber faces with the improved damage resistance observed with front faces following 'laser conditioning,' two schedules for CO₂-laser polishing of end faces were developed and evaluated. Finally, to improve resistance to damage at sites with significant static stresses, fiber samples which passed a much higher tensile proof test during manufacturing were tested. The current experiments were conducted with a new laser having a shorter pulse width and a significantly different mode structure. The beam was injected into the fiber using a geometry that had been successful in the previous study in minimizing a damage mechanism which can occur at the core/cladding interface with the first few hundred fiber diameters. However, the different mode structure of the new laser apparently resulted in this mechanism dominating the current results.

• Research Organization: Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 10119867
• Report Number(s): CONF-911064--4; SAND--92-0034C; ON: DE92007312
• Journal Information: Proceedings, Laser-Induced Damage in Optical Materials: 1991, Journal Name: Proceedings, Laser-Induced Damage in Optical Materials: 1991; ISSN 0277-786X
• Publisher: SPIE
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360201
360206
CARBON DIOXIDE LASERS
DAMAGE
Explosives
FIBERS
Fiber coupled lasers
Fiber couplers
Fiber lasers
LASER RADIATION
Laser damage threshold
Laser induced damage
Multimode fibers
OPTICAL FIBERS
PHYSICAL RADIATION EFFECTS
POLISHING
PREPARATION AND FABRICATION
Polishing
RADIATION EFFECTS
Resistance
SILICA
Step index fibers