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Optical and ultrasonic monitoring of femtosecond laser filamentation in fused silica
Millimeter-long filaments and accompanying luminous plasma and defect channels created in fused silica (FS) by single focused femtosecond laser pulses with supercritical powers were probed in situ using optical imaging and contact ultrasonic techniques. Above the threshold pulse energy E opt = 5 μJ...
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Published in: | Applied surface science 2009-09, Vol.255 (24), p.9721-9723 |
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Main Authors: | , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites |
Online Access: | Get full text |
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Summary: | Millimeter-long filaments and accompanying luminous plasma and defect channels created in fused silica (FS) by single focused femtosecond laser pulses with supercritical powers were probed in situ using optical imaging and contact ultrasonic techniques. Above the threshold pulse energy
E
opt
=
5
μJ corresponding to a few megawatt power levels pulses collapse due to self-focusing, producing channels filled by electron–hole plasma and luminescent defects, and exhibits predominantly compressive pressure transients. Analysis of the optical and ultrasonic response versus the laser pulse energy suggests that filamentary pulse propagation in the channels occurs with considerable dissipation of about ∼10
cm
−1. The predominant ionization mechanism is most likely associated with avalanche ionization, while the main mechanism of optical absorption is free-carrier absorption via inverse Bremsstrahlung interaction with the polar lattice. |
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ISSN: | 0169-4332 1873-5584 |
DOI: | 10.1016/j.apsusc.2009.04.057 |