CC BY
22LM-I-40
Ultrafast time-resolved microscopy during femtosecond laser structuring
M. Garcia-Lechuga,1* D. Puerto, 1>" J. Bonse,1* Y. Fuentes-Edfuf,1 J. Solis,1 and J. Siege!,'
1 - Laser Processing Group, Instituto de Óptica, IO-CSIC, Serrano 121, Madrid, Spain present address: Departamento de Física Aplicada, Universidad Autónoma, Madrid, Spain xpresent address: Polytechnic School of University, Alicante, Spain ^present address: Bundesanstalt für Materialforschung und -prüfung, Unter den Eichen 87, Berlin, Germany
j.siegel@io. cfmac. csic.es
Femtosecond laser processing of materials allows the fabrication of high-precision micro- and nano-structures for a wide field of applications. Yet, for an ultimate optimization of these structures, it is necessary to comprehend the complex transformation pathways of the material at the extreme excitation intensities used. Ultrafast time-resolved microscopy has proven to be a powerful technique for unraveling the mechanisms triggered by ultrashort laser pulses in dielectrics, semiconductors and metals [1]. The core technique is based on combining an optical pump-probe approach with optical microscopy, providing sub-ps temporal and ^m spatial resolution, which can be extended by different imaging modalities. Applied to surface processing, femtosecond microscopy has the capability of resolving temporally and spatially numerous processes such as electron excitation, heating, melting, ablation, and solidification [2,3]. It also has the ability to estimate the density and temporal evolution of laser-induced free-electron plasmas in dielectrics, visualize the optical Kerr effect, identify the occurrence of uncommon ablation mechanisms based on the expansion of a transparent thin shell, as well as resolving the formation of a heat-affected layer [4,5]. A further extension of the technique, denominated "ultrafast moving-spot microscopy", allows to study the formation dynamics of laser-induced periodic surface structures (LIPSS) [6]. We demonstrate in this talk that the visualization of the process dynamics obtained by time-resolved microscopy, covering fs to ^s temporal ranges, is extremely useful for an understanding of the origin of the morphological features and properties of the obtained structures, paving the way for the optimization strategies and applications (see Fig. 1).
ablation and resolidification oxide layer removal
Fig. 1: Scheme of the basic fs microscopy technique (top left) and results obtained for different materials.
[1] K. Sokolowski-Tinten, J. Bialkowski, A. Cavalleri, D. von der Linde, A. Oparin, J. Meyer-ter-Vehn, S. Anisimov, Transient States of Matter during Short Pulse Laser Ablation, Phys. Rev. Lett. 81, 224 (1998).
[2] J. Bonse, G. Bachelier, J. Siegel, J. Solis, Time- and space-resolved dynamics of melting, ablation, and solidification phenomena induced by femtosecond laser pulses in germanium, Phys. Rev. B 74, 134106 (2006).
[3] D. Puerto, J. Siegel, W. Gawelda, M. Galvan-Sosa, L. Ehrentraut, J. Bonse, J. Solis, Dynamics of plasma formation, relaxation, and topography modification induced by femtosecond laser pulses in crystalline and amorphous dielectrics, J. Opt. Soc. Am. B 27, 1065 (2010).
[4] M. Garcia-Lechuga, J. Siegel, J. Hernandez-Rueda, J. Solis, Imaging the ultrafast Kerr effect, free carrier generation, relaxation and ablation dynamics of Lithium Niobate irradiated with femtosecond laser pulses, J. Appl. Phys. 116, 10 (2014).
[5] M. Garcia-Lechuga, J. Solis, J. Siegel, Melt front propagation in dielectrics upon femtosecond laser irradiation: Formation dynamics of a heat-affected layer, Appl. Phys. Lett. 108, (2016).
[6] M. Garcia-Lechuga, D. Puerto, Y. Fuentes-Edfuf, J. Solis, J. Siegel, Ultrafast Moving-Spot Microscopy: Birth and Growth of Laser-Induced Periodic Surface Structures, ACS Photonics 3, 1961 (2016).
