Transient reflectivity and transmission changes during plasma formation and ablation in fused silica induced by femtosecond laser pulses |
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Authors: | D Puerto W Gawelda J Siegel J Bonse G Bachelier J Solis |
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Institution: | (1) Laser Processing Group, Instituto de óptica, CSIC, Serrano 121, 28006 Madrid, Spain;(2) Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Strasse 2A, 12489 Berlin, Germany;(3) Laboratoire de Spectrométrie Ionique et Moléculaire, UMR 5579 CNRS—Université Claude Bernard-Lyon 1, Batiment Alfred Kastler, 43 Boulevard du 11 Novembre 1918, 69622 Villeurbanne, Cedex, France |
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Abstract: | We have studied the plasma formation and ablation dynamics in fused silica upon irradiation with a single 120 fs laser pulse
at 800 nm by using fs-resolved pump-probe microscope. It allows recording images of the laser-excited surface at different
time delays after the arrival of the pump pulse. This way, we can extract both the temporal evolution of the surface reflectivity
and transmission, at 400 nm, for different spatial positions in the spots (and thus for different local fluences) from single
series of images. At fluences well above the visible ablation threshold, a fast and large increase of the reflectivity is
induced by the formation of a dense free-electron plasma. The maximum reflectivity value is reached within ≈1.5 ps, while
the normalized transmission decreases within ≈400 fs. The subsequent temporal evolution of both transient reflectivity and
transmission are consistent with the occurrence of surface ablation. In addition, the time-resolved images reveal the existence
of a free-electron plasma distribution surrounding the visible ablation crater and thus formed at local fluences below the
ablation threshold. The lifetime of this sub-ablation plasma is ≈50 ps, and its maximum electron density amounts to 5.5×1022 cm−3. |
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Keywords: | PACS" target="_blank">PACS 42 65 Re 42 70 Ce 52 38 Mf 52 50 Jm 61 80 Ba 79 20 Ds |
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