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Proceedings Paper

The damage mechanism in borosilicate glass generated by nanosecond pulsed laser at 1.064 μm
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Paper Abstract

We studied theoretically the laser-plasma interaction, and performed experiments to investigate the mechanisms giving rise to optical damage in Borosilicate glass using nanosecond laser pulses at wavelength 1064 nm. Our experimental result shows that the optical damage process generated by nanosecond laser pulses is the result of an optically induced plasma. The plasma is initiated when the laser irradiance frees electrons from the glass. Although it may be debated, the electrons are likely freed by multi-photon absorption and the number density grows via impact ionization. Later when the electron gas density reaches the critical density, the electron gas resonantly absorbs the laser beam through collective excitation since the laser frequency is equal to the plasma frequency. The laser energy absorbed through the collective excitation is much larger than the energy absorbed by multi-photon ionization and impact ionization. Our experimental result also shows the plasma survives until the end of the laser pulse and the optical damage occurs after the laser pulse ceases. The plasma decay releases heat to the lattice. This heat causes the glass to be molten and soft. It is only as the glass cools and solidifies that stresses induced by this process cause the glass to fracture and damage. We also show the experimental evidence of the change of the refractive index of the focusing region as the density of the electron gas changes from sub-critical to overcritical, and the reflection of the over-critical plasma. This reflection limits the electron gas density to be not much larger than the critical density.

Paper Details

Date Published: 4 December 2012
PDF: 20 pages
Proc. SPIE 8530, Laser-Induced Damage in Optical Materials: 2012, 853008 (4 December 2012); doi: 10.1117/12.979243
Show Author Affiliations
Binh T. Do, Sandia National Labs. (United States)
Mark Kimmel, Sandia National Labs. (United States)
Michael Pack, Sandia National Labs. (United States)
Randal Schmitt, Sandia National Labs. (United States)
Arlee V. Smith, AS-Photonics, LLC (United States)

Published in SPIE Proceedings Vol. 8530:
Laser-Induced Damage in Optical Materials: 2012
Gregory J. Exarhos; Vitaly E. Gruzdev; Joseph A. Menapace; Detlev Ristau; M J Soileau, Editor(s)

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