Optical and ultrasonic monitoring of femtosecond laser filamentation in fused silica |
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Authors: | Vygantas Mizeikis Saulius Juodkazis Sergey I Kudryashov Andrei A Ionin |
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Institution: | a Research Institute for Electronic Science, Hokkaido University, N21W10 CRIS Building, Sapporo 001-0021, Japan b Division of Global Research Leaders (Research Institute of Electronics), Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8561, Japan c Laser Research Center, Department of Quantum Electronics, Vilnius University, Saul?tekio 9, LT-2040 Vilnius, Lithuania, and Altechna Co., Ltd., Konstitucijos 23C-604, LT-08105 Vilnius, Lithuania d P.N. Lebedev Physical Institute, Russian Academy of Sciences, 119991 Moscow, Russia |
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Abstract: | 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 Eopt = 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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Keywords: | 52 50 Jm 61 82 Ms 52 35 Dm 52 38 Mf |
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