C.B. de Araujo

Temperature sensor based on frequency upconversion in Er/sup 3+/-doped fluoroindate glass

We describe the characterization of a temperature sensor based on the infrared-to-visible frequency upconversion process excited in a sample of Er/sup 3+/-doped fluoroindate glass. The present results demonstrate the feasibility of constructing a compact practical device using a low-power CW 1.48-/spl mu/m diode laser as the excitation source.

Nonresonant third-order nonlinear properties of NaPO3―WO3―Bi2O3 glasses in the near infrared

n2, was 10 �15 cm 2 / W and the NL absorption coefficient, 2, varied from 0.3 to 0.5 cm/GW for WO3 concentrations varying from 20% to 50%. The experiments in the infrared did not show relevant NL behavior for WO3 concentrations smaller than 50%. In this paper, we report on the third-order nonlinearity of NaPO3 –W O3 –B i2O3 glasses that present large NL response in the near infrared. The presence of Bi2O3 instead of BaF2 in the glass composition contributes for the increase in the NL response because of the larger Bi2O3 polarizability. The samples prepared have good optical quality, they are stable against moisture, and have large optical damage threshold. The experiments performed in the infrared indicate large values of n2 for the different compositions investigated. Two variations in the Z-scan technique at 1064 and 800 nm, with picosecond and femtosecond laser pulses, respectively, were applied for characterization of the samples. From the experiments, we determine n2 10 �15 cm 2 / W, one order of magnitude larger than silica, and negligible NL absorption coefficient. Figures of merit for all-optical switching were determined using the NL parameters measured and the results indicate large potential of NaPO3 –W O3 –B i2O3 glasses for photonic devices in the near infrared.

Giant enhancement of phonon-assisted one-photon excited frequency upconversion in a Nd3+-doped tellurite glass

Changing the samples temperature from 200 K to 535 K, we observed 670-fold enhancement of a phonon-assisted upconversion emission at ≈754 nm obtained from a Nd3+-doped tellurite glass excited by 5 ns laser pulses at 805 nm. A rate-equation model, including the relevant energy levels and temperature dependent transition rates, is proposed to describe the process. The results fit well with the data when one considers the nonradiative transitions contributing for the 754 nm luminescence are promoted by an effective phonon mode with energy of 700 cm−1.

Enhanced Photoluminescence and Planar Waveguide of Rare-Earth Doped Germanium Oxide Glasses with Metallic Nanoparticles

Abstract We review here the recent developments that demonstrate enhanced optical response of germanium oxide glasses containing rare-earth ions and metallic nanoparticles (NPs). The nucleation of silver and gold NPs was obtained in glassy compositions that incorporate different rare-earth ions species. Enhanced photoluminescence (PL) spectra, extending from the blue to the near-infrared, were obtained using samples with appropriate compositions. PL intensity enhancement up to 1000% was observed. Demonstration of the potential use of the glass samples as displayed with controlled colors and optical planar waveguides for integrated photonics in the optical communication range was also reviewed. The operation of an optical amplifier with enhanced gain due to the presence of gold NPs was characterized. In all the cases discussed here, the presence of metallic NPs was essential to improve the optical response of the samples, either by exploiting energy transfer processes from the NPs to the luminescent ions, or by the influence of the enhanced local field in the vicinity of the particles.

Creating and fixing a metal nanoparticle layer on the holes of microstructured fibers for plasmonic applications

Methods to insert, keep and fix silver and gold nanoparticles to the inner walls of microstructured fibers are demonstrated. Fibers optimized for evanescent field interaction were employed and can result in efficient plasmonic chemical sensing.

Biopolymer random laser consisting of Rhodamine 6G and silica nanoparticles incorporated to bacterial cellulose

We demonstrate random lasing action in a biopolymer that has large potential for medical applications. The novel random laser consists of nanofibers of bacterial cellulose impregnated with silica nanoparticles and Rhodamine 6G.

Optical parametric amplification in a random medium: BBO nanopowder

The emission and propagation of light in disordered media has always been a topic of interest in science, mainly because in nature this is the most common way of light emission and propagation. This research topic received a particular attention after the report of the first highly efficient random laser (RL) [1]. Indeed a large number of investigations discussing the fundamentals and the applications of RLs have been developed in the past decade. Among the motivations for such studies, we mention the RL simplicity and the low spatial coherence associated to its emission, which are indispensable requirements, for instance, on speckle-free full field imaging [2]. Here we present a new low-spatial-coherence-laser-based source, the random optical parametric emitter (ROPE) in a nanopowder consisting of ß-BaB2O4 (ß-BBO) 10-nm-nanocrystals.

High-order nonlinear scattering in ß-BBO nanocrystals

In this work we present an experimental and theoretical study on high-order hyper-Rayleigh scattering (HRS). This process also called harmonic light scattering, is an incoherent variant of harmonic generation process which occurs in bulk crystals. In general, HRS is addressed in the literature to the lowest-order nonlinear (NL) processes of molecules or nanoparticles, i.e., second harmonic scattering in noncentrosymmetric materials and third harmonic scattering in centrosymmetric systems [1, 2]. In the present work, we report the simultaneous emission of the second, third, fourth and fifth harmonic scattering in a sample consisting of beta barium borate (β-BBO) nanocrystals with dimensions of ≈10 nm. The optical excitation of the samples was performed at 2000 nm (100 fs pulses; repetition rate: 1.0 kHz), obtained via an OPA system pumped by a Ti:sapphire regenerative amplifier. The generated emission was observed at 1000 nm, 670 nm, 500 nm and 400 nm. In order to theoretically modeling the observed high-order optical harmonic generation and their dependence as a function of the excitation laser power, a generalized HRS approach was employed using the BBO second order properties as an internal self-reference parameter to quantify the high-order susceptibilities.

Fast transient bleaching in Rh-6G functionalized T1O2 nanoparticles: Charge transfer dynamics

Summary form only given. The charge-transfer mechanisms from dye to semiconductor nanoparticles and the time scales involved in these processes are a matter of interest for diverse applications, such as dye-sensitized solar cells (DSC) [1] and photocatalysis [2]. In DSC, the primary mechanism encompasses light-induced electron excitation following electron transfer from excited LUMO states of the dye to the conduction band (CB) of the semiconductor. To take place this electron transfer, the semiconductor CB must have a lower energy than the LUMO states of the sensitizer. Titanium dioxide (TiO2) often meets this requisition and therefore is the most widely semiconductor employed in DSC. Fast electron transfer is mandatory to avoid exciton recombination before charge-transfer and therefore, improve the efficiency of a DSC. Conversely, slow backward charge transfer (from the semiconductor to the dye) increases the efficiency of a DSC.the dye) increases the efficiency of a DSC.Charge transfer from rhodamine 590 (Rh6G) to amorphous TiO2 nanoparticles in colloidal suspension is investigated here via pump-probe transient absorption (TA). The TA kinetics is analyzed taking into account the relevant energy levels of the hybrid nanocomposite and electron transfer rates are estimated from the TA absorption signals. The pump-probe TA experimental apparatus used, as pump beam, a regeneratively amplified Ti:Sapphire laser (800 nm, 100 fs, 1 kHz repetition rate), which was frequency doubled (λ = 400 nm) by a 1 mm long nonlinear BiBO crystal. The pump beam was modulated by an optical chopper operating at 461 Hz and its optical path was controlled by a mechanical delay line. The probe beam was derived from an optical parametric amplifier (OPA) pumped by the Ti:Sapphire laser whose output beam wavelength was tuned to λ = 530 nm at the maximum of the S0-S1 transition of Rh6G. The photodiode signals of the reference and signal beams were sent to two different boxcar averagers. The analog processor output voltage was sent to a lock-in amplifier locked at the chopper frequency. With this system, absorbance changes as low as 10-5 could be accurately measured. To functionalize the TiO2 nanoparticles with rhodamine 6G, a modified methanolic dye solution (Si:Rh6G) was prepared by reacting the dye with a silane molecule (3-isocyanatepropyltriethoxysilane) according to [3]. After the reaction, 10 mL of the Si:Rh6G solution was mixed to 5 mL of the TiO2 colloidal solution. The dye is proposed to anchor to the TiO2 nanoparticles via OH groups at the particles surface formed during the hydrolysis reaction. The colloid was kept under reflux at 80 °C for 24 hours. The resulting colloid was washed several times and redispersed in ethanol. The normalized transient bleaching signal shows curves that could be fitted by exponential functions. In this case, the bleaching recovery time is ≈ (2.9 ± 0.5) ns, which is smaller than the rhodamine 590 lifetime in ethanol (≈ 4.0 ns). However, for the dye binded to TiO2, the signal could be fitted by a sum of two exponential functions plus an offset. The time constants derived from the exponential fits to the TA kinetics for the Rh6Gfunctionalized TiO2 particles were τ1 = (160 ± 70) ps and τ2 = (1.0 ± 0.2) ns. The faster decay is assigned as charge transfer from thermalized excited states of the dye to the TiO2 conduction band, while the slower one corresponds to the back electron transfer from TiO2 to the dye. Direct exciton recombination and triplet states also contribute to the slower decay dynamics. The offset is a signature that the bleaching recovery is not completed during the time scale investigated due to trapping of electrons at in-gap states of the semiconductor or trapping of molecules in triplet states. Using the values of extracted from the TA data, the charge transfer rate is in the range (0.5-6.0)x109 s-1. This value is smaller than the charge transfer rates for other classes of dyes, such as ruthenium complexes or donor-pi-aceptors, which are in the range 109-1013 s.

Efficient distributed feedback dye laser in silk fibroin films

We observed longitudinal single-mode operation in a distributed feedback dye laser consisting of silk fibroin films doped with Rhodamine 6G dye and infiltrated with silica or silver nanoparticles.