Buried waveguides in Nd:YLF crystals obtained by femtosecond laser writing under double line approach
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Buried waveguides in Nd:YLF crystals obtained by femtosecond laser writing under double line approach D. Biasetti · E. Neyra · J.R. Vázquez de Aldana · L. Roso · G.A. Torchia
Received: 11 August 2011 / Accepted: 3 August 2012 / Published online: 31 August 2012 © Springer-Verlag 2012
Abstract In this paper, we present buried waveguides fabricated by fs laser writing in Nd3+ doped YLF crystal under double line approach (Miura et al. in Appl. Phys. Lett. 71:3329–3331, 1997). The waveguides were made by focusing two consecutive optical breakdown tracks (OBT) separated by about 20 µm. To make the optimal OBT, we focused the fs-laser pulses 200 µm below surface at intensities above the OB threshold for the material and controlled the writing speed. The guiding structures were fabricated by using a Chirped Pulse Amplification (CPA) femtosecond (fs) laser system. We chose the optimal writing parameters in order to obtain suitable waveguides, using around 3 µJ energy and writing speed from 15 to 50 µm/s. After optically exploring the waveguides by end-fire coupling, the guiding structures showed good optical performance. Guiding index profiles were retrieved from modal analysis by using BeamProp (RSoft) commercial software. This spatial distribution of the index increment, taking into account a lower refractive barrier on the OBT region plus the compressed region between the tracks, was obtained correctly fitting profiles modes. Finally, optical spectroscopy measurements were also performed in the waveguides. The results showed that the luminescence properties of Nd3+ ions are preserved in the waveguides compared with the values obtained for bulk.
D. Biasetti · E. Neyra · G.A. Torchia () Centro de Investigaciones Ópticas CONICET La Plata-CIC, Camino Centenario y 506, MB Gonnet (1897), Pcia. Bs. As., Argentina e-mail: [email protected] J.R. Vázquez de Aldana · L. Roso CLPU and Servicio Láser de la Universidad de Salamanca, Plaza de la Merced s/n 35008 Salamanca, Spain
1 Introduction From the appearance of the Chirped Pulse Amplification femtosecond (fs) systems, the interaction of this kind of laser pulses with optical materials gives rise to an important research field which involves the fs laser writing interaction with optical materials. As it is well known, by using this technology, nonlinear processes are the main responsible for the material processing, thus it is possible to modify, in a controlled way, any optical materials by using this experimental procedure. This modification is firstly activated by the ionization process which can be reached via multiphoton absorption, avalanche or tunnel. After this process, optical modification, damage or breakdown can be achieved in the material, depending on the laser fluences used. During this process, hugely free electrons within the plasma promoted by the laser interaction are recombined in the network, so, the fast cooling and shock waves originated are the responsible for the formation of high density regions, residual stress, defects, amorphous zones, etc. in
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