Flexible random lasers in dye-doped bio-degradable cellulose nanocrystalline needles

M-ERA-NET2/0007/2016 POCI-01-0145-FEDER-007688 PTDC/CTM-BIO/6178/2014 PTDC/CTM-REF/30529/2017 UID/CTM/50025In this work, we developed and investigated a random laser based on rhodamine6G (Rh6G) in ethylene glycol (EG) solution with varying cellulose nanocrystalline (CNC) needles as scatterers in the lasing media. Besides the suspension-in-cuvette scheme, an alternative configuration was also employed: a dye-CNC flexible self-supported thick-film (70 µm) random laser made by drop casting of the CNCs + Rh6G + hydroxypropyl cellulose suspension. In relation to conventional scatterers, the biodegradable cellulose nanocompounds showed a comparable reduction in both the spectral full width at half-maximum and the energy threshold values, with an optimal concentration of 5 mg [CNC]/ml[EG] in suspension. Its performance was also compared with other cellulose-based random lasers, presenting advantages for some parameters. The flexible film configuration showed similar results, but contained 10% less Rh6G than the suspension.authorsversionpublishe

Optical fiber relative humidity sensor based on a FBG with a di-ureasil coating

In this work we proposed a relative humidity (RH) sensor based on a Bragg grating written in an optical fiber, associated with a coating of organo-silica hybrid material prepared by the sol-gel method. The organo-silica-based coating has a strong adhesion to the optical fiber and its expansion is reversibly affected by the change in the RH values (15.0–95.0%) of the surrounding environment, allowing an increased sensitivity (22.2 pm/%RH) and durability due to the presence of a siliceous-based inorganic component. The developed sensor was tested in a real structure health monitoring essay, in which the RH inside two concrete blocks with different porosity values was measured over 1 year. The results demonstrated the potential of the proposed optical sensor in the monitoring of civil engineering structures

Diffusive random laser modes under a spatiotemporal scope

At present the prediction and characterization of the emission output of a diffusive random laser remains a challenge, despite the variety of investigated materials and theoretical interpretations given up to now. Here, a new mode selection method, based on spatial filtering and ultrafast detection, which allows to separate individual lasing modes and follow their temporal evolution is presented. In particular, the work explores the random laser behavior of a ground powder of an organic-inorganic hybrid compound based on Rhodamine B incorporated into a di-ureasil host. The experimental approach gives direct access to the mode structure and dynamics, shows clear modal relaxation oscillations, and illustrates the lasing modes stochastic behavior of this diffusive scattering system. The effect of the excitation energy on its modal density is also investigated. Finally, imaging measurements reveal the dominant role of diffusion over amplification processes in this kind of unconventional lasers

One- and two-photon pumped random laser action in Rhodamine B doped di-ureasil hybrid

Trabajo presentado al: "SPIE Photonic West" celebrado en San Francisco (US) del 21 al 26 de Enero de 2012.One- and two-photon pumped random lasing have been demonstrated in a powder based on a Rhodamine B-doped diureasil hybrid by using a picosecond pump laser emitting either at 532 nm or 1064 nm under controlled experimental conditions. In both cases, we have used the same diffusive medium with identical spatial disorder, the same time-width and temporal profile for the pump pulse, as well as equal pump spot sizes. The corresponding onsets of laser-like emission and slope efficiencies are also investigated.This work was supported by the Spanish Government MEC under Projects No. MAT2009-14282-C02-02, FIS2011-27968, Consolider SAUUL CSD2007-00013, and Basque Country Government (IT-331-07).Peer Reviewe

Time-resolved random laser spectroscopy of inhomogeneously broadened systems

The understanding of energy transfer processes in biological systems occurring among optical centres which exhibit inhomogeneously broadened spectral bands is of paramount importance to determine time constants and spatial distribution of energy flow. A new time resolved-spectroscopy based on the random laser generation of the optical probes is reported. As an example, the excited state relaxation of Rhodamine B molecules in an organic-inorganic hybrid material is investigated. This kind of spectroscopy may resolve not only the spectral features of the system but also provide a high speed picture of the energy transfer and excited state relaxation of the involved optical probes. The results could be applied to other kind of efficient interacting chromophore pairs embedded in inhomogeneous scattering structures such as biological tissues

Coherence characteristics of random lasing in a dye doped hybrid powder

The photon statistics of the random laser emission of a Rhodamine B doped di-ureasil hybrid powder is investigated to evaluate its degree of coherence above threshold. Although the random laser emission is a weighted average of spatially uncorrelated radiation emitted at different positions in the sample, a spatial coherence control was achieved due to an improved detection configuration based on spatial filtering. By using this experimental approach, which also allows for fine mode discrimination and time-resolved analysis of uncoupled modes from mode competition, an area not larger than the expected coherence size of the random laser is probed. Once the spectral and temporal behavior of non-overlapping modes is characterized, an assessment of the photon-number probability distribution and the resulting second-order correlation coefficient as a function of time delay and wavelength was performed. The outcome of our single photon counting measurements revealed a high degree of temporal coherence at the time of maximum pump intensity and at wavelengths around the Rhodamine B gain maximum.This work was supported by the Spanish Government under project FIS2011-27968, by the Basque Country Government (IT-659-13) and Saiotek (S-PE11UN072), and by the Fundação para a Ciência e a Tecnologia (FCT, Portugal), FEDER and COMPETE, under contract Pest-C/CTM/LA0011/2013. SGR acknowledges the financial support from the Research Association MPC for a post-doctoral appointment.Peer reviewe

Optimal scheduling of industrial combined heat and power plants under time-sensitive electricity prices

This work reports on the infrared-to-visible CW frequency upconversion from planar waveguides based on Er3+-Yb3+-doped 100-xSiO(2)-xTa(2)O(5) obtained by a sol-gel process and deposited onto a SiO2-Si substrate by dip-coating. Surface morphology and optical parameters of the planar waveguides were analyzed by atomic force microscopy and the m-line technique. The influence of the composition on the electronic properties of the glass-ceramic films was followed by the band gap ranging from 4.35 to 4.51 eV upon modification of the Ta2O5 content. Intense green and red emissions were detected from the upconversion process for all the samples after excitation at 980 nm. The relative intensities of the emission bands around 550 nm and 665 nm, assigned to the H-2(11/2) -> I-4(15/2), S-4(3/2) -> I-4(15/2), and F-4(9/2) -> I-4(15/2) transitions, depended on the tantalum oxide content and the power of the laser source at 980 nm. The upconversion dynamics were investigated as a function of the Ta2O5 content and the number of photons involved in each emission process. Based on the upconversion emission spectra and 1931CIE chromaticity diagram, it is shown that color can be tailored by composition and pump power. The glass ceramic films are attractive materials for application in upconversion lasers and near infrared-to-visible upconverters in solar cells.FAPESPFAPESPCAPESCAPESCNPqCNP

CELLULOSE NANOCRYSTALS FROM BACTERIAL CELLULOSE

Bacterial cellulose produced from Gluconacetobacter xilinus was used to produce cellulose nanocrystals by sulfuric acid hydrolysis. Hydrolysis was performed with 64% sulfuric acid at 50 ºC with the hydrolysis time ranging between 5 and 90 min. The production of nanocrystals was observed to have size distributions that were dependent on hydrolysis times up to 10 min, after which time the suspensions showed distributions closer in size. Results from thermal analysis and X-ray diffraction showed that the amorphous cellulose was removed, leaving only the crystalline portion. Self-supported films were formed from the suspension of nanocrystals and had iridescence characteristics. The films were characterized by microscopy measures and specular reflectance

Determination of refractive index contrast and surface contraction in waveguide channels using multiobjective genetic algorithm applied to spectroscopic ellipsometry

The application of spectroscopic ellipsometry for the characterization of UV-patterned channel waveguides to obtain the refractive index contrast and surface deformation profile is presented. Thin films were prepared with organic-inorganic di-ureasils hybrids modified with zirconium tetra-propoxide deposited in silica on silicon substrates. The channel waveguides were produced by direct writing using UV laser radiation. The refractive index contrast and the surface ablation induced by the UV optical signal were estimated by ellipsometry being 4.5 x 10(-3) and 30.5 nm, respectively. The deepness of the surface ablation due to the UV exposition was also estimated by atomic force microscopy measurements that pointed out a value of 31.0 +/- 1.0 nm, concordant with the ellipsometric calculations. The near-field intensity technique was used as a support for contextualizing the proposed ellipsometry method for the characterization of refractive index profiles. The estimated refractive index contrast (2.0 x 10(-3)) is in a good agreement with the refractive index contrast derived from ellipsometry

Scale up the collection area of luminescent solar concentrators towards metre-length flexible waveguiding photovoltaics

Luminescent solar concentrators (LSCs) are cost-effective components easily integrated in photovoltaics (PV) that can enhance solar cells' performance and promote the integration of PV architectural elements into buildings, with unprecedented possibilities for energy harvesting in facade design, urban furnishings and wearable fabrics. The devices' performance is dominated by the concentration factor (F), which is higher in cylindrical LSCs compared with planar ones (with equivalent collection area and volume). The feasibility of fabricating long-length LSCs has been essentially limited up to ten of centimetres with F<1. We use a drawing optical fibre facility to easily scale up large-area LSCs (length up to 2.5m) based on bulk and hollow-core plastic optical fibres (POFs). The active layers used to coat the bulk fibres or fill the hollow-core ones are Rhodamine 6G- or Eu3+-doped organic-inorganic hybrids. For bulk-coated LSCs, light propagation occurs essentially at the POFs, whereas for hollow-core device light is also guided within the hybrid. The lower POFs' attenuation (similar to 0.1m(-1)) enables light propagation in the total fibre length (2.5m) for bulk-coated LSCs with maximum optical conversion efficiency ((opt)) and F of 0.6% and 6.5, respectively. For hollow-core LSCs, light propagation is confined to shorter distances (6-9x10(-2)m) because of the hybrids' attenuation (1-15m(-1)). The hollow-core optimised device displays (opt)=72.4% and F=12.3. The F values are larger than the best ones reported in the literature for large-area LSCs (F=4.4), illustrating the potential of this approach for the development of lightweight flexible high-performance waveguiding PV. Copyright (c) 2016 John Wiley \& Sons, Ltd