Material processing at the micro/nanometre scales has been revolutionised by the development of femtosecond lasers. The particular way in which these lasers pulses interact with matter allow the local modification of the physical properties of any material as well as its selective removal (ultrafast ablation) with minimal thermal or mechanical damage of the surrounding material.

Fundamental studies of the ablation process in dielectrics (Theoretical and Experimental). Although the effects of ultrafast laser ablation are well known, there are still many open questions about its mechanism due to the complexity of the process. We have developed numerical codes to calculate the distribution of energy and charge deposited in the material. Thus, it is possible to predict the evolution of the ablation craters in the multi-shot regime [1,2]. The theoretical studies are complemented with accurate measurements in the microprocessing station, space and time resolved spectroscopy of the ablation plume and shadowgraphy.

Applications of short pulse microprocessing (Experimental). We are working on a large variety of applications of ultrafast laser ablation, namely:

• Micromachining of metals, ceramics, polymers, organic materials, etc. for aerospace industries, microfluidics, microelectronics, implantology, etc. [3,4].
• Production of nanoparticles by aggregation in the ablation plume [5,6].
• Interaction with biological tissues and microsurgery [7,8].
• Surface nanostructuring of semiconductors and thin film polymers.
• Artwork restoration, by selective removal of patina layers [9-11].
• Fabrication of photonic elements, such as integrated waveguides in crystals and glasses [12-15].

Optimization of microprocessing techniques and new control tools (Experimental). We have incorporated the Laser Induced Breakdown Spectroscopy (LIBS) technique as a tool for in situ control and diagnostics in microprocessing, and we are developing software for controlling 4-axes micropositioning sytems and real-time energy control.

[1] J. R. Vázquez de Aldana, C. Méndez, L. Roso y P. Moreno, "Propagation of ablation channels with multiple femtosecond pulses in dielectrics: numerical simulations and experiments", J. Phys. D: Appl. Phys. 38, 2764 (2005).
[2] J. R. Vázquez de Aldana, C. Méndez, L. Roso, "Saturation of ablation channels micro-machined in fused silica with many femtosecond laser pulses", Opt. Exp. 14, 1329 (2006).
[3] P. Moreno, C. Méndez, A. García, I. Arias and L. Roso, "Femtosecond laser ablation of carbon reinforced polymers", Appl. Surf. Sci. 252, 4110 (2006).
[4] R. A. Delgado et al., "Zirconia Dental Implants with Femtosecond Laser Microstructuring", Journal of Biomedical Materials Research: Part B - Applied Biomaterials 96, 91-100 (2011).
[5] F. A. Videla et al., "Analysis of the main optical mechanisms responsible for fragmentation of gold nanoparticles by femtosecond laser radiation", J. Appl. Phys. 107, 114308 (2010).
[6] M. Galcerán et al., "Synthesis of Monoclinic KGd(WO4)2 Nanocrystals by Two Preparation Methods", Journal of Nanoparticle Research 11, 717 (2009).
[7] J. Arellano et al., "Femtosecond laser disruption of filamentous cyanobacteria unveils dissimilar cellular stability between heterocysts and vegetative", Photochemistry and Photobiology 84, 1576-1582 (2008).
[8] M. Portillo et al., "Morphological alterations in dentine after mechanical treatment and ultrashort pulse laser irradiation" Laser Med. Sci. (2010).
[9] S. Gaspard et al., "Interaction of Femtosecond Laser Pulses with Tempera Paints", Appl. Surf. Sci. 255, 2675 (2008).
[10] M. Walczak et al., "Evaluation of Femtosecond Laser Pulse Irradiation of Ancient Parchment" Appl. Surf. Sci. 255, 3179 (2008).
[11] M. Oujja et al., "UV laser removal of varnish on tempera paints with nanosecond and femtosecond pulses", Phys. Chem. Chem. Phys. 13, 4625 (2011).
[12] A. Benayas et al., "Thermally resistant waveguides fabricated in Nd:YAG ceramics by crossing femtosecond damage filaments", Opt. Lett. 35, 330 (2010).
[13] W. Silva et al., "Femtosecond-laser-written, stress induced Nd:YVO waveguides preserving fluorescence and Raman gain", Opt. Lett. 35, 916-918 (2010).
[14] Y. Tan et al., "Continuous wave laser generation at 1064 nm in femtosecond laser inscribed Nd:YVO4 channel waveguides", Appl. Phys. Lett. 97, 031119 (2010).
[15] N. Dong et al., "Femtosecond laser writing of multifunctional optical waveguides in a Nd:YVO4+KTP hybrid system", Opt. Lett. 36, 975 (2011).