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7 pages, 6 figures.-- PACS: 68.35.Rh; 79.20.Ds; 78.47.+p; 64.70.Dv; 61.80.Ba ; This work describes a novel technique allowing to measure with picosecond resolution the time evolution of the optical properties (reflectivity/transmission) of a material surface exposed to a single laser pulse. The experimental setup is based on the use of a streak camera in combination with a single-mode probe cw laser. The maximum achievable time resolution is about 1 ps for the acquisition of a single event. Results concerning melting of Ge films under ps pulses will be used to illustrate the potential of this measurement technique for resolving single optical transient events in the ps time scale. The advantages of the system with respect to the use of pump-and-probe optical measurements are especially remarkable for the study of events occurring in time windows with full widths from 1 to 10 ns, as it is the case for rapid solidification phenomena induced by ultrashort laser pulses. This has allowed us to investigate in detail, for instance, the occurrence of bulk and surface initiated solidification phenomena in thin amorphous Ge films. ; This work has been partially supported by CICIYT and CSIC (Spain) under Project No. IN94-0205. One of the authors (J. S.) acknowledges with pleasure the funding of the European Union through a Marie Curie Fellowship (ERB40001GT54352) within the TMR Program. ; Peer reviewed

6 pages, 4 figures.-- PACS: 64.70.Dv; 68.55.-a; 81.05.Cy; 61.43.Dq; 81.05.Gc; 78.66.Jg; 78.66.Db; 42.62.-b ; The dynamics of melting-rapid solidification of amorphous Ge films on transparent substrates upon irradiation with nanosecond laser pulses has been analyzed by means of real time reflectivity measurements performed both at the air-film and film-substrate interfaces. The effect of the heat flow conditions on the rapid solidification process has been studied by comparing the behavior of films with thicknesses ranging from 50 to 180 nm on substrates with different thermal conductivities like glass, quartz, and sapphire. The films deposited onto substrates of low thermal conductivity (glass and quartz) undergo a local delayed melting process in the vicinity of the film-substrate interface, the process being dependent on the film thickness and/or the laser fluence. This delayed melting process is never observed in films deposited on sapphire. The comparison of the results suggests that the solidification heat released from the primary melt is responsible for the delayed melting process at the film-substrate interface whenever the heat-transfer ratio to the substrate is low enough. ; The Marie Curie TMR program for the European Union (ERB40001GT54352) is acknowledged for financial support. ; Peer reviewed

5 pages, 4 figures. ; Real time reflectivity measurements with subnanosecond time resolution have been used to determine the reflectivity at the melting temperature RS(Tm) of single crystalline Ge and Si at 514.5 nm. Due to the excellent time resolution and sensitivity achieved in a single exposure experiment, the reflectivity of the solid just before melting could be measured. Values of RS(Tm)=0.470±0.006 and RS(Tm)=0.440±0.008 for c-Ge and c-Si have, respectively, been determined. These values, together with those determined by heating in vacuum in the range 300–800 K, are compared to those reported earlier in the literature and the differences are discussed. ; This work has been partially supported by the European Union under Contract No. TMR ERB-CT98-0188. N. Chaoui acknowledges the funding by the same contract. J. Siegel acknowledges the funding of the European Union through the TMR program (ERB-0001GT954352). ; Peer reviewed

S. V. Kirner et al. -- 13 pags., 14 figs., 2 tabs. ; Ultrashort laser pulses with durations in the fsto- ps range were used for large area surface processing of steel aimed at mimicking the morphology and extraordinary wetting behaviour of bark bugs (Aradidae) found in nature. The processing was performed by scanning the laser beam over the surface of polished flat sample surfaces. A systematic variation of the laser processing parameters (peak fluence and effective number of pulses per spot diameter) allowed the identification of different regimes associated with characteristic surface morphologies (laser-induced periodic surface structures, i.e., LIPSS, grooves, spikes, etc.). Moreover, different laser processing strategies, varying laser wavelength, pulse duration, angle of incidence, irradiation atmosphere, and repetition rates, allowed to achieve a range of morphologies that resemble specific structures found on bark bugs. For identifying the ideal combination of parameters for mimicking bug-like structures, the surfaces were inspected by scanning electron microscopy. Inparticular, tilted micrometre-sized spikes are the best match for the structure found on bark bugs. Complementary to the morphology study, the wetting behaviour of the surface structures for water and oil was examined in terms of philic/ phobic nature and fluid transport. These results point out a route towards reproducing complex surface structures inspired by nature and their functional response in technologically relevant materials. ; This work has received funding from the Horizon 2020 European Union's research and innovation programme under Grant Agreement No. 665337 ("LiNaBioFluid"; URL: http://www.laserbiofluid. eu). ; Peer reviewed

4 págs,; 5 figs. ; Ridge waveguide lasers have been fabricated on Nd doped LiNbO crystals. The fs-laser writing technique was used to define ridge structures on a gradient-index planar waveguide fabricated by Zn-diffusion. This planar waveguide was formed in a z-cut LiNbO substrate homogeneously doped with a 0.23% of Nd ions. To obtain lateral light confinement, the surface was then micromachined using a multiplexed femtosecond laser writing beam, forming the ridge structures. By butting two mirrors at the channel waveguide end-facets, forming a waveguide laser cavity, TM-polarized laser action at 1085 nm was achieved by end-fire TM-pumping at 815 nm. The waveguide laser shows a threshold of 31 mW, with a 7% of slope efficiency. © 2016 Elsevier B.V. All rights reserved ; This work was supported by the Spanish Government under projects TEC2014-52642-C2-1-R and MAT2013-47395-C4. ; Peer Reviewed

4 págs.; 6 figs.; OCIS codes: (240.6680) Surface plasmons; (300.6340) Spectroscopy, infrared; (130.3060) Infrared; (130.6010) Sensors. ; A novel fiber-coupled indium tin oxide (ITO) coated glass slide sensor for performing surface plasmon polariton chemical monitoring in the ∼3.5 μm mid-infrared (IR) range is reported. Efficient mid-IR fiber coupling is achieved with 3D laser written waveguides, and the coupling of glass waveguide modes to ITO surface plasmon polaritons (SPPs) is driven by the varying phase matching conditions of different aqueous analytes across the anomalous dispersion range determined by their molecular fingerprints. By means of using both a mid-IR fiber supercontinuum source and a diode laser, the excitation of SPPs is demonstrated. The sensor sensitivity is tested by discriminating CH from OH features of ethanol in water solutions, demonstrating an instrumental ethanol limit of detection of 0.02% in a wide concentration range of at least 0%-50%. The efficient optical monitoring of mid-IR SPPs in smart glass could have a broad range of applications in biological and chemical sensing. © 2016 Optical Society of America ; Spanish Government (MAT2013-47395-C4-4-R, TEC2014-52642-C2-1-R, TEC2014-55948-R); Catalan Government (2009SGR235, 2014FI_B00274); European Commission (EC) (ACP2-GA-2013-314335-JEDI ACE). ; Peer Reviewed

This work describes the phase transitions occurring at the film-substrate interface of amorphous germanium films upon nanosecond laser-pulse-induced melting of the surface. Films with thickness ranging from 50 to 130 nm deposited on glass substrates were studied. Real-time reflectivity measurements with subnanosecond time resolution performed both at the air-film and film-substrate interfaces were used to obtain both surface and in-depth information of the process. In the thicker films (≥80 nm), the enthalpy released upon solidification of a shallow molten surface layer induces a thin buried liquid layer that self-propagates in-depth towards the film-substrate interface. This buried liquid layer propagates with a threshold velocity of 16±1 ms and causes, eventually, melting at the film-substrate interface. In the thinnest film (50 nm) there is no evidence of the formation of the buried layer. The presence of the self-propagating buried layer for films thicker than 80 nm at low and intermediate laser fluences is discussed in terms of the thermal gradient in the primary melt front and the heat released upon solidification. © 2005 American Institute of Physics. ; This work has been partially supported by the MCYT through Project No. DPI: DPI2002-00151 and by the European Union in the framework of the TMR ERB FMRX Contract No. CT098-0188 "Laser Cleaning" Network. N. C. acknowledges the funding of the European Union through the latter contract. ; Peer Reviewed

Rapid solidification dynamics in amorphous germanium films melted by nanosecond laser pulses was analyzed. Single-shot subnanosecond time resolved reflectivity measurements were carried out. Results showed that once a minimum depth was induced, a bulk solidification process followed by the release of solidification enthalpy was found. ; This work has been partially supported by the European Union in the framework of the TMR ERB FMRX CT098- 0188 ''Laser Cleaning'' Network. N.C. acknowledges the funding of the European Union through the same contract. ; Peer Reviewed

3 pages, 3 figures. ; We report on the mechanisms responsible for the formation of optical waveguides upon femtosecond laser irradiation of an alkaline lead-oxide silicate glass. MicroRaman spectroscopy and nonlinear fluorescence were employed to probe the local glass network structure and the formation of optically active defects respectively. At low laser pulse energies, the laser modified region is formed by a single light guiding region, whereas for pulses above 14 µJ the modified region is formed by a central dark zone, which does not guide light, accompanied by light guiding zones located in the surrounding of the dark one. This behavior is different from that observed in common silica glass systems but agrees with recent results obtained in phosphate and heavy metal oxide glasses. However, our results show that, unlike the latter glass, local densification of the glass occurs in the whole laser modified region, i.e., in the dark and the guiding zones. The suppression of light guiding in the dark region is explained by a high density of absorbing color centers. ; This work was partially supported by CICYT (Spain) under Project No. DPI2002-00151. One of the authors (V.D.B.) acknowledges the financial support of the CSIC and the European Social Fund through an I3P Ph.D. fellowship. Another author (P.L.-A. acknowledges funding from the Spanish Government ( the Ramón y Cajal program and Grant No. TIC2003-07485). ; Peer reviewed

4 pags., 4 figs. ; The potential for a subpicosecond amorphous-to-crystalline, disorder-to-order transition was explored by measuring the dielectric function of a-GeSb films following femtosecond laser excitation. Subpicosecond nonthermal structural changes both above and below the threshold for permanent crystallization were observed. ; The work at Harvard is supported by the National Science Foundation (Contract No. DMR-9807144) and the Army Research Office (Contract No. DAAG55-98-1-0077). A. M.-T. Kim recognizes support from the Deutscher Akademischer Auslandsdienst (DAAD) and J. Siegel from the European Union through the TMR Program (Grant No. ERB40001GT954352). ; Peer Reviewed

We have produced rib waveguides by femtosecond-laser structuring of active (Yb,Nb):RbTiOPO4 /RbTiOPO4 epitaxial layers. The ribs were produced by the approximation scanning technique combined with beam multiplexing. The so-obtained waveguides are trapezoidal in shape and show propagation losses with an upper bound of ∿4 dB/cm. A simulation of the rib waveguides with real geometry parameters reveals high levels of light confinement at 632 and 972 nm. The near-field patterns of the fundamental modes have been obtained by exciting the waveguides at wavelengths of 632 and 972 nm. Micro-Raman spectroscopy study reveals that the damage to the crystalline structure in the rib boundaries, showing no amorphization traces, is around 3 ο m in length and depth, which is significantly shorter than the total width of the ribs. © 2012 IEEE ; This work was supported by the Spanish Government under Projects TEC2010-21574-C02-02, TEC2011-22422, MAT2011-29255-C02-02, PI09/90527, and the Catalan Authority under Project 2009SGR235. This work was also supported in part by the European Commission under the Seventh Framework Programme under Project FP7-SPACE-2010-1-GA-263044. The work of J. Cugat was supported by the Spanish Government under the FPI fellowship BES-2009-024190. ; Peer Reviewed