Anderson S. L. Gomes

Random fiber laser

We investigate the effects of two-dimensional confinement on the lasing properties of a classical random laser system operating in the incoherent feedback (diffusive) regime. A suspension of 250 nm rutile (TiO2) particles in a rhodamine 6G solution was inserted into the hollow core of a photonic crystal fiber generating the first random fiber laser and a novel quasi-one-dimensional random laser geometry. A comparison with similar systems in bulk format shows that the random fiber laser presents an efficiency that is at least 2 orders of magnitude higher.

Frequency upconversion in Er3+ doped PbO–GeO2 glasses containing metallic nanoparticles

The authors report the infrared-to-visible frequency upconversion (UPC) process in Er3+ doped PbO–GeO2 glasses containing silver nanoparticles (NPs) with an average diameter of 2.2nm. The absorption spectra of the samples present a band centered at 470nm due to the surface plasmons associated with the NPs. The intensity of the band grows with increasing NP concentration. The experiments were performed by exciting the samples with a 980nm diode laser and observing the UPC emissions in the red-green region. The enhanced UPC intensity is attributed to the local field effect in the proximity of the NPs.

Blue upconversion enhancement by a factor of 200 in Tm3+-doped tellurite glass by codoping with Nd3+ ions

We investigated near-infrared-to-blue upconversion from thulium (Tm3+) doped in tellurite glasses upon continuous wave excitation near 800 nm. We observed an enhancement of over two orders of magnitude of the upconverted emission at ∼480 nm when neodymium (Nd3+) ions were codoped with Tm3+ ions. For comparison, using a Tm3+:Nd3+ codoped fluorozirconate glass as a reference material we observed a 40-fold enhancement of the blue emission. Analysis of the blue emission for samples with different doping levels of Nd3+ ions showed that energy transfer between Nd3+ and Tm3+ is the mechanism responsible for the enhancement in upconversion.

Evaluation of enamel dental restoration interface by optical coherence tomography

Evaluation of molar dental restorations on enamel is performed using optical coherence tomography (OCT) with 10 microm resolution. Images of approximately 50 microm failure gaps in the restorations are demonstrated and the OCT images are compared with x-ray and optical microscopy pictures. The results demonstrate the potential of the technique for clinical evaluation of dental restorations.

Imaging carious human dental tissue with optical coherence tomography

Optical coherence tomography is an imaging technology that produces high-resolution cross-sectional images of turbid media and internal microstructures including inside living tissue. In this work, three-dimensional images of a dental microstructure, that can be used to make both qualitative and quantitative assessments of oral tissue health, were obtained. It was possible to detect subclinical caries in third molar human teeth, showing that the lesion is located below the surface at 10μm with a maximum depth lesion of 50μm. A three-dimensional image was constructed confirming that it is possible to observe different planes inside the sample. It is important to notice that the optical changes induced by the carious disease in dental tissue can be readily detected by the optical coherence tomography method, before structural changes become apparent.

Random laser action in dye solutions containing Stöber silica nanoparticles

Random laser action is obtained in a diffusive weakly scattering regime using an alcohol solution of rhodamine 640 with silica nanoparticles prepared by the Stober method, with different average diameters of 49, 90, 219, and 490 nm. Particle size and concentration has proven to affect the random laser performance. It is also shown that silica nanoparticles contributes for a much slower photodegradation of the dye molecules than titania nanoparticles that has been used in the majority of the dye random lasers. This fact makes it advantageous to use silica nanoparticles for the fundamental studies of random laser, due to its increase in lifetime under pumping conditions.Random laser action is obtained in a diffusive weakly scattering regime using an alcohol solution of rhodamine 640 with silica nanoparticles prepared by the Stober method, with different average diameters of 49, 90, 219, and 490 nm. Particle size and concentration has proven to affect the random laser performance. It is also shown that silica nanoparticles contributes for a much slower photodegradation of the dye molecules than titania nanoparticles that has been used in the majority of the dye random lasers. This fact makes it advantageous to use silica nanoparticles for the fundamental studies of random laser, due to its increase in lifetime under pumping conditions.

Evaluation of crack propagation in dental composites by optical coherence tomography

OBJECTIVES The purpose of this study was to image the sites of fracture initiation and slow crack propagation in a fiber reinforced composite, using the optical coherence tomography (OCT) technique. METHODS Bar specimens (2mm x 3mm x 25mm) of fiber reinforced composite were mechanically and thermally cycled to emulate oral conditions. The interior of these samples was analyzed prior to and after loading, using OCT. The device used was a home-built Fourier domain OCT setup working at 800 nm with 6 microm spatial resolution. RESULTS Intact specimens after load cycling were analyzed. It was clearly seen that OCT images provide an insight into crack propagation, which is not seen by the naked eye. SIGNIFICANCE By using OCT the possibility of analyzing the fracture propagation quantitatively, and in depth, was added, opening up possibilities to quantitative studies.

Third-order nonlinear optical properties of bismuth-borate glasses measured by conventional and thermally managed eclipse Z scan

Third-order nonlinearity one order of magnitude larger than silica is measured in bismuth-borate glasses presenting a fast response (<200 fs). The results for the sign and magnitude of the nonlinearity were obtained using a combination of the eclipse Z scan with thermal nonlinearity managed Z scan, whereas the Kerr shutter technique was employed to obtain the electronic time response of the nonlinearity, all performed with 76 MHz repetition rate 150 fs pulses at 800 nm. Conventional Z scans in the picosecond regime at 532 and 1064 nm were also independently performed, yielding the values of the third-order nonlinear susceptibilities at those wavelengths. The results obtained for the femtosecond response, enhanced third-order nonlinearity of this glass (with respect to silica), place this glass system as an important tool in the development of photonics devices. Electro-optical modulators, optical switches, and frequency converters are some of the applications using second-order nonlinear properties of the Bi-glass based on the rectification model.

Marginal analysis of resin composite restorative systems using optical coherence tomography

OBJECTIVES To analyze marginal integrity of resin composites dental restorations using optical coherence tomography (OCT). METHODS Thirty extracted human premolars had occlusal cavities prepared and were randomly divided according to the restorative systems evaluated: Filtek P90™/P90 Adhesive System™, Filtek Z350™, and Filtek Z250™/Single Bond™ (3M/ESPE). The teeth were then stored in the dark for 24h in 0.9% saline solution. Restorations were finished and polished and stored again for 24h before thermocycling (500 cycles, 5-55°C). A commercially available OCT system was used (SR-OCT: OCP930SR/Thorlabs) with 930nm central wavelength. Cross-sectional images were obtained every 250μm and evaluated using Image J. A-scans were analyzed using the Origin 8.0 program, after a filter treatment using Matlab. RESULTS The qualitative analysis of the internal margins did not observe gaps even after A-scan examination, although distinctive patterns were found for each restorative system. Penetration of Single Bond and Filtek P90 self-etch primer into dentin was also observed. A thick adhesive layer was found for Filtek P90 bonding agent. SIGNIFICANCE Considering the characteristics of the OCT system, the setup used in this study was capable of evaluating the marginal integrity of resin composite restorations and detecting some interaction between dental bonding agents and dental substrates. OCT can be considered a promising method for the evaluation of the internal margins of restorations in vivo.

Evaluation of the integrity of dental sealants by optical coherence tomography

OBJECTIVES The purpose of the present research was to demonstrate images of failures into the structure of pit and fissure sealants using optical coherence tomography (OCT). METHODS Five human third molars were selected and the sealant ALPHA SEAL LIGHT/DFL was applied according to the manufacturer instructions. For evaluation of the structure of pit and fissure sealants, twenty OCT images of each tooth were performed before and after application of sealant. A total of 200 images were evaluated. A home built spectral OCT system used was operating in spectral domain (SD-OCT), at 840 nm and a measured spatial resolution of 10 μm. The system is based on the Michelson interferometer set-up and is controlled by the software OCT 800--Complex Square/LabView, that collects data and generates the image. The occlusal surfaces were scanned in a bucco-lingual direction and tomographic images parallel to long axis of tooth were obtained. After the achievement of the images by OCT, the crown of each tooth was sectioned in a occlusogingival direction (buccolingually). Images from each section were obtained and evaluated by an optical microscope. OCT and microscopic images were compared. RESULTS Representative images showed that OCT image provides the insight into sealant material. It was possible to clearly identify the internal structure of sealant and the subjacent enamel. Sealant and enamel are very well distinguished, and failures at the interior and at surface are well detected. SIGNIFICANCE OCT could generate images of the features of fissures, bubbles and failures in the adaptation of sealants, opening up possibilities in the future to monitoring sealant application and retention in short and long term.