Microstructural imaging of high repetition rate ultrafast laser written LiTaO<inf>3</inf> waveguides

The microstructural changes associated with the formation of lithium tantalate waveguides after high repetition rate ultrafast laser inscription has been investigated by confocal micro-Raman experiments. While the laser beam focal volume is characterized by significant lattice damage, no reduction of Raman mode strength has been observed at the guiding region, suggesting the preservation of the nonlinear optical coefficient in the waveguide. A general blueshift of the Raman modes has been observed at the guiding region, suggesting lattice compression as the dominant mechanism of waveguide formation. © 2009 American Institute of Physics

Three-dimensional microstructuring of yttrium aluminum garnet crystals for laser active optofluidic applications

The following article appeared in Applied Physics Letters 103.4 (2013): 041101 and may be found at http://scitation.aip.org/content/aip/journal/apl/103/4/10.1063/1.4816338We demonstrate three-dimensional microstructuring in a neodymium doped yttrium aluminum garnet (Nd:YAG) crystal. Spatially well-defined hollow microstructures deeply embedded within the material are shown to result from the creation of a pre-damage state within the Nd:YAG crystal network that is validated using luminescence and Raman analyses of the structures. This opens up the potential of fabricating next-generation optofluidic devices in optical gain materialsFinancial support from the Spanish Ministerio de Educación under the Programa de Movilidad de Recursos Humanos del Plan Nacional de IþDþi 2008/2011 for abroad postdoctoral researchers. This work was also supported by the Universidad Autónoma de Madrid and Comunidad Autónoma de Madrid (Project S2009/MAT- 1756) and by the Spanish Ministerio de Educación y Ciencia (MAT2010-16161

High repetition rate UV ultrafast laser inscription of buried channel waveguides in Sapphire: Fabrication and fluorescence imaging via ruby R lines

We report on the fabrication of buried cannel waveguides in Sapphire crystals by 250-kHz high repetition rate ultrafast laser inscription with 385 nm pulses. The propagation properties of the waveguides were studied as a function of the writing conditions. The micro-fluorescence analysis of the R lines generated by trace Cr3+ dopant in Sapphire is used to elucidate the micro-structural modifications induced in the crystal network. It is revealed that waveguide has been formed due to local dilatation of the Sapphire network generated in the surroundings of the focal volume. The refractive index increment due to the dilatation induced electronic polarizability enhancement has been estimated to be of the order of Δn ≈10-4. © 2009 Optical Society of America

LaF3 core/shell nanoparticles for subcutaneous heating and thermal sensing in the second biological-window

We report on Ytterbium and Neodymium codoped LaF3 core/shell nanoparticles capable of simultaneous heating and thermal sensing under single beam infrared laser excitation. Efficient light-to-heat conversion is produced at the Neodymium highly doped shell due to non-radiative de-excitations. Thermal sensing is provided by the temperature dependent Nd3+ → Yb3+ energy transfer processes taking place at the core/shell interface. The potential application of these core/shell multifunctional nanoparticles for controlled photothermal subcutaneous treatments is also demonstratedThis work was supported by the Spanish Ministerio de Economıa y Competitividad (MAT2013-47395-C4-1-R), by Brazilian Agencies: FINEP (Financiadora de Estudos e Projetos) through the Grant Nos. INFRAPESQ-11 and INFRAPESQ-12; CNPq (Conselho Nacional de Desenvolvimento Cientıfico e Tecnologico) Grants INCT NANO(BIO)SIMES and Project Universal No. 483238/2013-9; CAPES (Coordenadoria de Aperfeiçoamento de Pessoal de Ensino Superior) by means of the Project PVE No. A077/2013. Erving C. Ximendes is supported by a Ph.D. scholarship from CNPq and currently by the PVE A077/2013 Project by means of a Ph.D. sandwich program developed at the Universidad Autonoma de Madrid, Spain. Prof. Dr. Daniel Jaque is the PVE (Pesquisador Visitante Especial) of the Project No. A077/2013. Dr. K. U. Kumar is a post-doctoral fellow of this Project. Dr. Ueslen Rocha is supported by a Post Doctoral Fellowship grant PDE/CAPES at the Universidad Autonoma de Madrid-Spain through the Project No. 2108-14-

Thermal stability of microstructural and optical modifications induced in sapphire by ultrafast laser filamentation

We report on the thermal stability of both structural and optical micromodifications created by ultrafast laser written filaments in sapphire crystals. By using the Cr3+ traces as optical probes, we have concluded that the filaments are constituted by both reversible and nonreversible defects with very different spatial locations. The strain field measured from the analysis of R lines has been found to be erased at the same time when the reversible centers are recombined (∼1100 °C). This fact seems to indicate that these defects act as pinning centers for the induced stress. Furthermore, we have found that the waveguide generated in the proximity of the filament disappear for annealing temperatures above 1100 °C. This clearly supports the assumption that waveguiding is produced by the strain stress induced refractive index increment based on the dominant electronic polarizability enhancement. © 2010 American Institute of Physics

All-optical thermal microscopy of laser-excited waveguides

We report on a unique combination of high-resolution confocal microscopy and ratiometric luminescence thermometry to obtain thermal images of 800 nm pumped ultrafast laser-inscribed waveguides in a Nd:YAG crystal. Thermal images evidence a strong localization of thermal load in the waveguide active volume. Comparison between experimental data and numerical simulations reveals that ultrafast laser-inscribed damage tracks in Nd:YAG crystals behave both as low-index and low-thermal conductivity barriersThis work was supported by the Spanish Ministerio de Economía y Competitividad (MINECO) under grants MAT2013-47395-C4-1-R and FIS2013-44174-P and from Junta de Castilla y León (Project SA116U13, UIC016

Quantum-dot based nanothermometry in optical plasmonic recording media

We report on the direct experimental determination of the temperature increment caused by laser irradiation in a optical recording media constituted by a polymeric film in which gold nanorods have been incorporated. The incorporation of CdSe quantum dots in the recording media allowed for single beam thermal reading of the on-focus temperature from a simple analysis of the two-photon excited fluorescence of quantum dots. Experimental results have been compared with numerical simulations revealing an excellent agreement and opening a promising avenue for further understanding and optimization of optical writing processes and media

Two-photon luminescence thermometry: towards 3D high-resolution thermal imaging of waveguides

We report on the use of the Erbium-based luminescence thermometry to realize high resolution, three dimensional (3D) thermal imaging of optical waveguides. Proof of concept is demonstrated in a 980-nm laser pumped ultrafast laser inscribed waveguide in Er:Yb phosphate glass. Multi-photon microscopy images revealed the existence of well confined intra-waveguide temperature increments as large as 200°C for moderate 980-nm pump powers of 120 mW. Numerical simulations and experimental data reveal that thermal loading can be substantially reduced if pump events are separated more than the characteristic thermal time that for the waveguides investigated is in the millisecond time scaleThis work has been supported by the Ministerio de Economía y Competitividad of Spain (MINECO) (FIS2013-44174-P, MAT2013-47395-C4-1-R) and National Natural Science Foundation of China (NSFC) (11274203

Raman scattering from phonons and magnons in RFe3)BO3)4

Inelastic light scattering spectra of several members of the RFe3(BO3)4 family reveal a cascade of phase transitions as a function of temperature, starting with a structural, weakly first order, phase transition followed by two magnetic phase transitions. Those consist of the ordering of the Fe-spin sublattice revealed by all the compound, and a subsequent spin-reorientational transition for GdFe3(BO3)4. The Raman data evidence a strong coupling between the lattice and magnetic degrees of freedom in these borates. The Fe-sublattice ordering leads to a strong suppression of the low energy magnetic scattering, and a multiple peaked two-magnon scattering continuum is observed. Evidence for short-range correlations is found in the `paramagnetic' phase by the observation of a broad magnetic continuum in the Raman data, which persists up to surprisingly high temperatures.Comment: 17 pages, 13 figure

Absorption efficiency of gold nanorods determined by quantum dot fluorescence thermometry

In this work quantum dot fluorescence thermometry, in combination with double-beam confocal microscopy, has been applied to determine the thermal loading of gold nanorods when subjected to an optical excitation at the longitudinal surface plasmon resonance. The absorbing/heating efficiency of low (≈3) aspect ratio gold nanorods has been experimentally determined to be close to 100%, in excellent agreement with theoretical simulations of the extinction, absorption, and scattering spectra based on the discrete dipole approximation