Emission cross sections and spectroscopy of Ho3+ laser channels in KGd(WO4)2 single crystal

The spectroscopic properties of Ho3+ laser channels in KGd(WO4)2 crystals have been investigated using optical absorption, photoluminescence, and lifetime measurements. The radiative lifetimes of Ho3+ have been calculated through a Judd-Ofelt (JO) formalism using 300-K optical absorption results. The JO parameters obtained were Ω2=15.35×10-20 cm2, Ω 4=3.79×10-20 cm2, Ω6 =1.69×10-20 cm2. The 7-300-K lifetimes obtained in diluted (8·1018 cm-3) KGW:0.1% Ho samples are: τ(5F3)=0.9 μs, τ( 5S2)=19-3.6 μs, and τ(5F5 )=1.1 μs. For Ho concentrations below 1.5×1020 cm-3, multiphonon emission is the main source of non radiative losses, and the temperature independent multiphonon probability in KGW is found to follow the energy gap law τph -1(0)=βexp(-αΔE), where β=1.4×10-7 s-1, and α=1.4×103 cm. Above this holmium concentration, energy transfer between Ho impurities also contributes to the losses. The spectral distributions of the Ho3+ emission cross section σEM for several laser channels are calculated in σ- and π-polarized configurations. The peak a σEM values achieved for transitions to the 5I8 level are ≈2×10-20 cm2 in the σ-polarized configuration, and three main lasing peaks at 2.02, 2.05, and 2.07 μm are envisaged inside the 5I7→5I8 channel.This work was supported by Comisión Interministerial de Ciencia y Tecnología under Projects MAT99-1077 and 2FD97-0912.Peer reviewe

Electrostática y EAO : una experiencia de simulación

In this work the inclusion of educational software in the teaching of physics is analyzed. The program used corresponds to the computer simulation of electrostatic fields, and it was applied to students of first year of universitary level in a Faculty of Chemistry

Efficient tunable laser operation of Tm:KGd(WO4)2 in the continuous-wave regime at room temperature

Tm:KGd(WO/sub 4/)/sub 2/ is studied as a three-level laser on the /sup 3/F/sub 4/ /spl rarr/ /sup 3/H/sub 6/ transition and a tunable source in the 2-/spl mu/m spectral range, operating at room temperature. An overall tunability extending from 1790 to 2042 nm is achieved with maximum output powers of 400 mW for an absorbed pump power of 1 W. Various doping levels, pump wavelengths and polarization configurations are compared and the advantages of the monoclinic double tungstates over other Tm-hosts are outlined

New strategies invonving upconverting nanoparticles for determining moderate temperatures by luminescence thermometry

Producción CientíficaHere we analyze alternative luminescence thermometry techniques to FIR, such as intensity ratio luminescence thermometry between the emission arising from two electronic levels that are not necessarily thermally coupled, but that show different evolutions with temperature, and lifetime luminescence nanothermometry in (Ho,Tm,Yb):KLu(WO4)2 and (Er,Yb):NaY2F5O nanoparticles. (Ho,Tm,Yb):KLu(WO4)2 nanoparticles exhibited a maximum relative sensitivity of 0.61% K−1, similar to that achievable in Er-doped systems, which are the upconverting systems presenting the highest sensitivity. From another side, (Er,Yb):NaY2F5O nanocrystals show great potentiality as thermal sensors at the nanoscale for moderate temperatures due to the incorporation of additional non-radiative relaxation mechanisms that shorten the emission lifetime generated by the oxygen present in the structure when compared to (Er,Yb):NaYF4 nanoparticles exhibiting the highest upconversion efficiency. We used those nanoparticles for ex-vivo temperature determination by laser induced heating in chicken breast using lifetime-based thermometry. The results obtained indicate that these techniques might constitute alternatives to FIR with potential applications for the determination of moderate temperatures, with sensitivities comparable to those that can be achieved by FIR or even higher.Ministerio de Economía, Industria y Competitividad (Projects MAT2013-47395-C4-1-4-R, and TEC2014-55948-R)Catalan Government (Projects no. 2014SGR1358 and 2013FI_B 01032

Formation of polycrystalline TiO2 on the ablated surfaces of RbTiOPO4 single crystals by thermal annealing

We investigated the structural effects that ultrafast laser ablation has on RbTiOPO4 (RTP) single crystals. Raman scattering analysis revealed that a polycrystalline layer of RTP substituted the original material on the surface of the microstructured areas which is mainly responsible for the roughness observed in these structures. A later annealing treatment on the ablated samples resulted in the formation of a layer of sub-micrometric particles of TiO2 in a mixed form of anatase and rutile, due to the decomposition of the polycrystalline RTP layer. This allows the development of engineering strategies to fabricate RTP–TiO2 composites, with mixed properties, that might allow the combination of the non-linear optical properties of RTP and the light dispersive and electrical properties of TiO2.This work was supported by the EU Framework 7 under project FP7-SPA-2010-263044, by the Spanish Government under projects MAT2011-29255-C02-02, TEC2010-21574-C02-02, FIS2009-09522 and CSD2007-00013, by Generalitat de Catalunya under project 2009SGR235 and by Junta de Castilla y León under project SA086A12-2

Mapping Temperature Distribution Generated by Photothermal Conversion in Graphene Film Using Er,Yb:NaYF4 Nanoparticles Prepared by Microwave-Assisted Solvothermal Method

This study analyzes the mapping of temperature distribution generated by graphene in a glass slide cover after illumination at 808 nm with a good thermal resolution. For this purpose, Er,Yb:NaYF4 nanoparticles prepared by a microwave-assisted solvothermal method were used as upconversion luminescent nanothermometers. By tuning the basic parameters of the synthesis procedure, such as the time and temperature of reaction and the concentration of ethanol and water, we were able to control the size and the crystalline phase of the nanoparticles, and to have the right conditions to obtain 100% of the β hexagonal phase, the most efficient spectroscopically. We observed that the thermal sensitivity that can be achieved with these particles is a function of the size of the nanoparticles and the crystalline phase in which they crystallize. We believe that, with suitable changes, these nanoparticles might be used in the future to map temperature gradients in living cells while maintaining a good thermal resolution

Surface ablation of RbTiOPO4 by femtosecond laser

We report here the results obtained in surface ablation of RbTiOPO4 single crystals by femtosecond laser. We fabricated and characterized one-dimensional (1D) diffraction gratings with different lattice spacings of 15 and 20 μm, and with a sub-modulation of the period introduced in the later. The optical and electronic microscopy characterization and filling factor analysis of these diffraction gratings are reported. We also show that the roughness generated on the grooves by the ablation process can be improved by chemical etching.This work was partially funded by the European Commission under the Seventh Framework Program under Project Cleanspace FP7-SPACE-2010-1-GA-263044, supported by the Spanish Government under Projects PI09/90527, TEC2009-09551, AECID A/024560/09, FIS2009-09522, HOPE CSD2007-00007 and SAUUL CSD2007-00013 (Consolider-Ingenio 2010), by Catalan Government under Projects 2009SGR235 and 2009SGR549, by Junta de Castilla y León under Project GR27, and by the Research Center on Engineering of Materials and Systems (EMaS) of the URV. J.J.C. is supported by the Education and Science Ministry of Spain and European Social Fund under the Ramón y Cajal program, RYC2006-858. We also acknowledge support from the Centro de Laseres Pulsados, CLPU, Salamanca, Spain

Thermal and Optical Characterization of Undoped and Neodymium-Doped Y3ScAl4O12 Ceramics

Y3–3xNd3xSc1Al4O12 (x = 0, 0.01, and 0.02) ceramics were fabricated by sintering at high temperature under vacuum. Unit cell parameter refinement and chemical analysis have been performed. The morphological characterization shows micrograins with no visible defects. The thermal analysis of these ceramics is presented, by measuring the specific heat in the temperature range from 300 to 500 K. Their values at room temperature are in the range 0.81–0.90 J g1–K–1. The thermal conductivity has been determined by two methods: by the experimental measurement of the thermal diffusivity by the photopyroelectric method, and by spectroscopy, evaluating the thermal load. The thermal conductivities are in the range 9.7–6.5 W K–1 m–1 in the temperature interval from 300 to 500 K. The thermooptic coefficients were measured at 632 nm by the dark mode method using a prism coupler, and the obtained values are in the range 12.8–13.3 × 10–6 K–1. The nonlinear refractive index values at 795 nm have been evaluated to calibrate the nonlinear optical response of these materials.This work is supported by the Spanish Government under projects MAT2011-29255-C02-01-02, MAT2013-47395-C4-4-R, and the Catalan Government under project 2014SGR1358. It was also funded by the European Commission under the Seventh Framework Programme, project Cleanspace, FP7-SPACE-2010-1-GA No. 263044

Optical absorption of Er3+ in RbTiOPO4 and KTiOPO4

The optical absorption of Er3+ in RbTiOPO4 (RTP) and KTiOPO4 (KTP) single crystals has been characterized at 5 K and 300 K temperatures. The room temperature oscillator strengths of Er3+ obtained in both lattices are similar although in KTP the uncertainty is higher due to the lower concentration of Er in the samples available. The results obtained in RTP have been analysed by using the Judd-Ofelt theory. The effective Judd-Ofelt parameters obtained for Er3+ in RTP are Omega(2)(eff) 12.85 x 10(-20) cm(2), Omega(4)(eff) = 0.60 x 10(-20) cm(2), Omega(6)(eff) = 0.57 x 10(-20) cm(2) The photoluminescence transition radiative rates, branching ratios and radiative lifetimes of Er3+ in, these crystals have been calculated for all de-excitations from the (4)G(9/2) multiplet. The I-4(13/2) -->(4) I-15/2 erbium emission has been characterized. The low temperature optical absorption and photoluminescence suggest the coexistence of two erbium centres in both lattices, which we have tentatively ascribed to the occupancy with different population densities of the two titanium lattice sites.This work has been supported by CICyT under project number TIC96-1039.Peer reviewe