Functionalizing Glass by Local Compositional Tuning with Ultrafast Lasers

CLEO 2019 in San Jose, CA (USA), 5–10 May 2019Abstract (35 Word Limit): This work reports the design, synthesis, laser processing and performance of borate glasses that were compositionally designed to be femtosecond laser writable using laser-induced ion migration, leading to the production efficient optical waveguide

Relation between nonlinear refractive index and third-order susceptibility in absorbing media

Expressions relating complex third-order optical susceptibility (χ(3) = χR (3) + iχ I (3)) with nonlinear refractive index (n2) and nonlinear absorption coefficient (β) have been formulated that eliminate the commonly used approximation of a negligible linear absorption coefficient. The resulting equations do not show the conventional linear dependence of χR (3) with n2 and χI (3) with β. Nonlinear refraction and absorption result instead from the interplay between the real and imaginary parts of the first- and third-order susceptibilities of the material. This effect is illustrated in the case of a metal-dielectric nanocomposite for which n2 and β values were experimentally obtained by Z-scan measurements and for which the use of the new formulas for χR (3) and ≤ Ig(3) yield a large correction and a sign reversal for χI (3). © 2004 Optical Society of America.This work has been supported by the Ministerio de Ciencia y Tecnologı´a of Spain (DPI2002-00151, TIC2002- 03235). R. del Coso acknowledges the financial support of the Consejerı´a de Educacio´n de la Comunidad de Madrid and the European Social Fund (ESF).Peer Reviewe

Slow interfacial reamorphization of Ge films melted by ps laser pulses

Melting and rapid solidification is induced in 50-nm-thick amorphous Ge films on glass substrates by single laser pulses at 583 nm with a duration of 10 ps. The solidification process is followed by means of reflectivity measurements with ns time resolution both at the air/film (front) and the substrate/film (back) interfaces. Due to interference effects between the light reflected at the film-substrate and film-liquid interfaces, the back side reflectivity measurements turn out to be very sensitive to the melt depth induced by the laser pulse and their comparison to optical simulations enables the determination of the solidification dynamics. For low fluences, only a thin layer of the film is melted and solidification occurs interfacially leading to reamorphization of the molten material. The results provide a critical interface velocity for amorphization of ∼4 m/s, much slower than the one that has widely been reported for elementary semiconductors. For high fluences, the molten layer depth approaches the film thickness and the results are consistent with a bulk solidification process. In this case, recalescence effects upon solid phase nucleation become important and lead to the formation of crystallites distributed throughout the whole resolidified volume. © 1998 American Institute of Physics.Jan Siegel acknowledges the funding of the European Community through a grant (ERB40001GT954352) within the Training and Mobility of Researchers Program. This work has been partially supported by CICYT (Spain) under project TIC93-0125.Peer Reviewe

Can the transformation time in phase change optical recording be improved by using femtosecond laser pulses?

CLEO/EUROPE ; EQEC European Quantum Electronics Conference, Munich ICm, Germany, 22-27 June, 2003N

Pressure-induced transient structural change of liquid germanium induced by high-energy picosecond laser pulses

The temporal evolution of the reflectivity of germanium at 514 nm upon irradiation with single high-energy picosecond laser pulses has been measured using a streak camera. It is found that, for a well-defined high fluence range, the reflectivity of the laser-induced molten phase attains a value of 0.85, considerably above the value reported for liquid Ge in thermal equilibrium (0.75). This behavior is consistent with a strong densification of the liquid phase remaining after the explosive vaporization of a thin surface layer. Within the specified fluence interval, this anomalously high reflectivity state is independent of the fluence and lasts tens of nanoseconds. Both characteristics point to the presence of a pressure-induced transient structural change in liquid germanium. © 2005 American Institute of Physics.Peer Reviewe

Nanocrystal size dependence of the third-order nonlinear optical response of Cu:Al2O3 thin films

3 pages, 3 figures.Metal nanocomposite thin films formed by Cu nanocrystals embedded in an amorphous Al2O3 host have been synthesized by pulsed laser deposition. The mean nanocrystal diameter d was varied in the range 3.0 ± 0.6 to 6 ± 1 nm. The linear and nonlinear optical properties of the films were studied in the vicinity of the surface plasmon resonance and the size dependence of the third-order nonlinear optical susceptibility of the metal nanocrystals has been determined. The observed dependence (1/d3) indicates that in the studied diameter interval, the nonlinear response is due to quantum confinement effects in which the major contribution is associated with electronic intraband transitions.This work has been partially supported by CICYT (Spain) under TIC 96-0467 project and by the EU under BRPR-CT98-0616 project. We acknowledge Dr. I. Vickridge (University of Paris VI et VII, France) for his assistance with RBS techniques.Peer reviewe

In situ studies of the crystallization kinetics in Sb-Ge films

The crystallization process in SbxGe1-x alloy films has been observed during in situ annealing in a transmission electron microscope. Results are presented for two films with x=0.89 (89 at. % Sb) and x=0.71 (71 at. % Sb), which lie on either side of the eutectic composition (x=0.85). In the former films radial crystals are observed to grow rapidly from discrete nuclei, whereas in the latter films the crystallization process occurs through a near-planar front. In addition, quantitative data obtained from these experiments show that the Sb0.89Ge0.11 films have a higher activation energy for crystal growth and a lower temperature for the nucleation of crystals. Significant differences are observed between the crystallization processes for the two films studied, with the Sb0.89Ge0.11 film showing better potential for development as an ultrafast optical phase-change storage medium. © 1995 American Institute of Physics.This work has been partially supported by CICYT under the TIC93-0125 project. We are grateful to The British Council/Spanish Joint Research Program for traveling fi- nances, the Glasstone Benefaction (AKPL), Professor R. J. Brook for provision of laboratory facilities, and the Materials Modelling Laboratory at Oxford for computing facilities. Dr. Neil Long is thanked for operation of the FEG STEM and production of the composition map shown in Fig. 6.Peer Reviewe

Surface structuring of fused silica with asymmetric femtosecond laser pulse bursts

Fused silica surface structuring has been performed using temporally shaped femtosecond laser pulses. For this purpose we have designed pulse bursts with a triangular intensity envelope and different slope sign and interpulse separation that were experimentally generated using a home-made temporal pulse shaper. We have found that pulse bursts with decreasing intensity envelopes are remarkably more efficient in terms of surface ablation than bursts with increasing intensity envelopes. The results reveal that laser energy coupling in the material is enhanced as the interpulse spacing decreases. A study of the ablation depth using stretched single pulses was carried out and compared to results obtained for pulse bursts with different interpulse spacing. We find that the deepest crater was achieved with bursts of 0.5 ps interpulse separation and decreasing envelope. This pulse form also induced the largest change of the surface reflectivity after irradiation. The results are discussed in terms of how the laser energy coupling efficiency is linked to the temporal pulse shape. © 2013 Optical Society of America.This work has been partially supported by the Spanish TEC2011-22422 project. J. H.-R. acknowledges a grant awarded by the Spanish Ministry of Science and Innovation.Peer Reviewe

Simultaneous time-space resolved reflectivity and interferometric measurements of dielectrics excited with femtosecond laser pulses

13 pags., 7 figs., 1 tab.Simultaneous time-and-space resolved reflectivity and interferometric measurements over a temporal span of 300 ps have been performed in fused silica and sapphire samples excited with 800 nm, 120 fs laser pulses at energies slightly and well above the ablation threshold. The experimental results have been simulated in the frame of a multiple-rate equation model including light propagation. The comparison of the temporal evolution of the reflectivity and the interferometric measurements at 400 nm clearly shows that the two techniques interrogate different material volumes during the course of the process. While the former is sensitive to the evolution of the plasma density in a very thin ablating layer at the surface, the second yields an averaged plasma density over a larger volume. It is shown that self-trapped excitons do not appreciably contribute to carrier relaxation in fused silica at fluences above the ablation threshold, most likely due to Coulomb screening effects at large excited carrier densities. For both materials, at fluences well above the ablation threshold, the maximum measured plasma reflectivity shows a saturation behavior consistent with a scattering rate proportional to the plasma density in this fluence regime. Moreover, for both materials and for pulse energies above the ablation threshold and delays in the few tens of picoseconds range, a simultaneous >low reflectivity> and >low transmission> behavior is observed. Although this behavior has been identified in the past as a signature of femtosecond laser-induced ablation, its origin is alternatively discussed in terms of the optical properties of a material undergoing strong isochoric heating, before having time to substantially expand or exchange energy with the surrounding media.This work has been partly funded by Laserlab-Europe (Grant Agreement No. 284464, EU’s Seventh Framework Programme, Project No. SLIC002014), by the Spanish Ministry of Economy and Competiveness (Project No. TEC2014-52642- C2-1-R) as well as by the Danish Council for Independent Research | Natural Sciences. M.G.-L. acknowledges the FPU (Formación de Profesorado Universitario) Grant No. AP2012- 0217 awarded by the Spanish Ministry of Education.Peer Reviewe

Controlling the transmission at the surface plasmon resonance of nanocomposite films using photonic structures

3 pages, 3 figures, 1table.The transmission of nanocomposite thin films formed by Cu nanocrystals embedded in an amorphous aluminum oxide (Al2O3) matrix has been enhanced in the vicinity of the surface plasmon resonance wavelength, by the design of one-dimensional photonic structures. The nanocrystals are distributed in layers, whose separation and periodicity are used to control the optical response of the films. It is found that at the SPR a transmission enhancement up to 36% can be achieved with respect to a film with an homogeneous distribution of the nanocrystals. These photonic structures have been successfully produced by pulsed laser deposition.D. E. Hole is acknowledged for performing RBS measurements. This work has been supported by Project No. TIC2002-03235, CICYT (Spain).Peer reviewe