Special Section on Laser Damage III

Mass removal by oxidation and sublimation of porous graphite during fiber laser irradiation

[+] Author Affiliations
Grady T. Phillips, Charles D. Fox

Air Force Institute of Technology, Department of Engineering Physics, 2950 Hobson Way, Wright-Patterson Air Force Base, Ohio 45433-7765, United States

Oak Ridge Institute for Science and Education, 1299 Bethel Valley Road, Oak Ridge, Tennessee 37831-0117, United States

William A. Bauer, Ashley E. Gonzales, Nicholas C. Herr, Glen P. Perram

Air Force Institute of Technology, Department of Engineering Physics, 2950 Hobson Way, Wright-Patterson Air Force Base, Ohio 45433-7765, United States

Ryan C. Gosse

Air Force Research Laboratory, Aerospace Systems Directorate, 2210 8th Street, B20146, Wright-Patterson Air Force Base, Ohio 45433, United States

Opt. Eng. 56(1), 011013 (Aug 26, 2016). doi:10.1117/1.OE.56.1.011013
History: Received May 4, 2016; Accepted August 8, 2016
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Abstract.  The various effects of laser heating of carbon materials are key to assessing laser weapon effectiveness. Porous graphite plates, cylinders, and cones with densities of 1.55 to 1.82  g/cm3 were irradiated by a 10-kW fiber laser at 0.075 to 3.525  kW/cm2 for 120 s to study mass removal and crater formation. Surface temperatures reached steady state values as high as 3767 K. The total decrease in sample mass ranged from 0.06 to 6.29 g, with crater volumes of 0.52 to 838  mm3, and penetration times for 12.7-mm-thick plates as short as 38 s. Minor contaminants in the graphite samples produced calcium and iron oxide to be redeposited on the graphite surface. Dramatic graphite crystalline structures are also produced at higher laser irradiances. Significantly increased porosity of the sample is observed even outside the laser-irradiated region. Total mass removed increases with deposited laser energy at a rate of 4.83  g/MJ for medium extruded graphite with an apparent threshold of 0.15 MJ. At 3.5  kW/cm2, the fractions of the mass removed from the cylindrical samples in the crater, surrounding trench, and outer region of decreased porosity are 38%, 47%, and 15%, respectively. Graphite is particularly resistant to damage by high power lasers. The new understanding of graphite combustion and sublimation during laser irradiation is vital to the more complex behavior of carbon composites.

© 2016 Society of Photo-Optical Instrumentation Engineers

Citation

Grady T. Phillips ; William A. Bauer ; Charles D. Fox ; Ashley E. Gonzales ; Nicholas C. Herr, et al.
"Mass removal by oxidation and sublimation of porous graphite during fiber laser irradiation", Opt. Eng. 56(1), 011013 (Aug 26, 2016). ; http://dx.doi.org/10.1117/1.OE.56.1.011013


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