Tunable Visible Light and Energy Transfer Mechanism in Tm3+ and Silver Nanoclusters within Co-Doped GeO2-PbO Glasses.

This study introduces a novel method for producing Ag nanoclusters (NCs) within GeO2-PbO glasses doped with Tm3+ ions. Sample preparation involved the melt-quenching method, employing adequate heat treatment to facilitate Ag NC formation. Absorption spectroscopy confirmed trivalent rare-earth ion incorporation. Ag NC identification and the amorphous structure were observed using transmission electron microscopy. A tunable visible emission from blue to the yellow region was observed. The energy transfer mechanism from Ag NCs to Tm3+ ions was demonstrated by enhanced 800 nm emission under 380 and 400 nm excitations, mainly for samples with a higher concentration of Ag NCs; moreover, the long lifetime decrease of Ag NCs at 600 nm (excited at 380 and 400 nm) and the lifetime increase of Tm3+ ions at 800 nm (excitation of 405 nm) corroborated the energy transfer between those species. Therefore, we attribute this energy transfer mechanism to the decay processes from S1→T1 and T1→S0 levels of Ag NCs to the 3H4 level of Tm3+ ions serving as the primary path of energy transfer in this system. GeO2-PbO glasses demonstrated potential as materials to host Ag NCs with applications for photonics as solar cell coatings, wideband light sources, and continuous-wave tunable lasers in the visible spectrum, among others.

Characterization of the photoelastic dispersion coefficient using polarized digital holography.

The photoelastic dispersion coefficient represents the relationship between stress and the differences in refractive indices in a birefringent material. However, determining the coefficient using photoelasticity is challenging, as it is difficult to determine the refractive indices within photoelastic samples that are under tension. Here we present, for the first time, to our knowledge, the use of polarized digital holography to investigate the wavelength dependence of the dispersion coefficient in a photoelastic material. A digital method is proposed to analyze and correlate the differences in mean external stress with differences in mean phase. The results confirm the wavelength dependence of the dispersion coefficient, with an accuracy improvement of 25% compared to other photoelasticity methods.

Dynamic stable ring resonator for high-power continuous single-frequency lasers: conditions for a compact resonator.

When considering dynamically stable resonators, ring lasers are good choices because they have a stability interval that is twice as large as that of linear resonators and sensitivity to misalignment decreasing with pump power; however, the literature does not provide easy design guidelines. A ring resonator utilizing Nd:YAG side pumped by diodes allowed single-frequency operation. The output single-frequency laser had good output characteristics; however, the overall length of the resonator did not allow for building a compact device with low misalignment sensitivity and larger spacing between longitudinal modes which could improve single-frequency performance. Based on previously developed equations, which allow for ease of design of a ring dynamically stable resonator, we discuss how to build an equivalent ring resonator, aiming to building a shorter resonator with the same stability zone parameters. The study of the symmetric resonator containing a pair of lenses allowed us to find the conditions to build the shortest possible resonator.

High-power Nd:YLF four-level lasers with 68% slope efficiency.

Three laser resonators are demonstrated emitting at 1053 nm and pumped at 797 nm by volume Bragg grating-equipped diodes, achieving the highest reported efficiencies for Nd:YLF in a four-level system, to the best of our knowledge. A peak output power of 880 W is achieved by pumping the crystal with a diode stack of 1.4 kW of peak pump power.

Silver Nanoclusters Tunable Visible Emission and Energy Transfer to Yb3+ Ions in Co-Doped GeO2-PbO Glasses for Photonic Applications.

This work investigates the optical properties of Yb3+ ions doped GeO2-PbO glasses containing Ag nanoclusters (NCs), produced by the melt-quenching technique. The lack in the literature regarding the energy transfer (ET) between these species in these glasses motivated the present work. Tunable visible emission occurs from blue to orange depending on the Yb3+ concentration which affects the size of the Ag NCs, as observed by transmission electron microscopy. The ET mechanism from Ag NCs to Yb3+ ions (2F7/2 → 2F5/2) was attributed to the S1→T1 decay (spin-forbidden electronic transition between singlet-triplet states) and was corroborated by fast and slow lifetime decrease (at 550 nm) of Ag NCs and photoluminescence (PL) growth at 980 nm, for excitations at 355 and 405 nm. The sample with the highest Yb3+ concentration exhibits the highest PL growth under 355 nm excitation, whereas at 410 nm it is the sample with the lowest concentration. The restriction of Yb3+ ions to the growth of NCs is responsible for these effects. Thus, higher Yb3+ concentration forms smaller Ag NCs, whose excitation at 355 nm leads to more efficient ET to Yb3+ ions compared to 410 nm. These findings have potential applications in the visible to near-infrared regions, such as tunable CW laser sources and photovoltaic devices.

Characterization of sound enamel and natural white spot lesions / Caracterização de esmalte hígido e lesões de mancha branca naturais

Objective: To compare optical, morphological, chemical, and physical aspects of the sound enamel and white spot lesions (WSL) classified as ICDAS 2. Material and Methods: Seventeen human molars with one surface presenting WSL and a sound surface (2 x 2 mm window) were characterized by Quantitative light-induced fluorescence (QLF ®), Optical coherence tomography (OCT), microhardness, and Raman spectroscopy. The ANOVA and Tukey's test were used at 5% significance level. Results: The QLF comparison between distinct substrates yielded decreased ∆Q (integrated fluorescence loss) of -15,37%mm2 and -11,68% ∆F (fluorescence loss) for WSL. The OCT detected mean lesion depth of 174,43 µm. ANOVA could not detect differences in the optical attenuation coefficient between the substrates (p>0.05). Lower microhardness measures were observed in WSL than on sound enamel (p<0.05). The Raman spectra showed four vibrational phosphate bands (v1, v2, v3, v4), where the highest peak was at 960.3 cm-1(v1) for both substrates. However, a 40% decrease in phosphate (v1) was detected in WSL. The peak at 1071 cm-1 was higher for sound enamel, indicating the presence of a phosphate band instead of the B-type carbonate. The spectra showed higher intensity of the organic composition at 1295 cm-1 and 1450 cm -1 for WSL. Conclusion: Non-invasive QLF, OCT and Raman spectroscopy were able to distinguish differences in fluorescence, optical properties, and organic/inorganic components, respectively, between sound enamel and WSL, validated by the destructive microhardness analysis. (AU)

Objetivo: Comparar os aspectos ópticos, morfológicos, químicos e físicos do esmalte sadio e das lesões de mancha branca naturais, classificada como ICDAS 2. Material e métodos: Dezessete molares humanos com uma face apresentando uma lesão de mancha branca natural e outra face o esmalte hígido (2 x 2 mm) foram caracterizados utilizando a Fluorescência quantitativa induzida pela luz (QLF ®), Tomografia de coerência óptica (OCT), Microdureza e Espectroscopia Raman. A ANOVA e o teste de Tukey foram utilizados ao nível de significância de 5%. Resultados: A comparação entre os substratos distintos, utilizando o QLF ® demonstrou uma diminuição no ∆Q (perda de fluorescência integrada) de -15,37%mm2 e -11,68% de ∆F (Perda de fluorescência) para a lesão de mancha branca. O OCT detectou uma profundidade média de lesão de 174,43µm. A ANOVA não detectou diferenças no coeficiente de atenuação óptica entre os substratos (>0,05). Microdureza significantemente menor foi detectada nas lesões de mancha branca do que no esmalte sadio (p<0,05). Os espectros Raman mostraram quatro bandas vibracionais do fosfato (v1,v2,v3,v4), onde o maior pico foi em 960,3cm-1para ambos os substratos. No entanto, uma diminuição de 40% no fosfato (v1) foi detectada na lesão. O pico em 1071cm-1foi maior para o esmalte hígido, demonstrando tratar-se da banda do fosfato, ao invés do carbonato tipo B. Os espectros apresentaram maior intensidade da composição orgânica em 1295cm-1e 1450 cm-1para a lesão de mancha branca. Conclusão:Os métodos não invasivos QLF, OCT e espectroscopia Raman foram capazes dediferenciar a fluorescência, propriedades ópticas e conteúdo orgânico/inorgânico do esmalte sadio comparado com esmalte com lesões de mancha branca, sendo validado pela análise de microdureza. (AU)

Dynamically stable single frequency ring resonator from diode pumped Nd:YAG modules with 55.6 W of output power.

A Nd:YAG rod single-frequency ring laser based on side-pumped commercial modules is presented. Thermally induced birefringence compensation was applied in a dynamically stable resonator providing 55.6 W of continuous, linearly polarized, TEM00 output. The particular case of a symmetric ring resonator containing one or two focusing rods and a pair of curved mirrors was analyzed and a design technique is presented, allowing for easy, continuous shaping of the stability limits by changing only the distances in the resonator.

Dynamically stable Nd:YAG resonators with beam quality beyond the birefringence limit and pumping of a singly resonant optical parametric oscillator.

A simple, reliable, linearly polarized laser source with very high beam quality is demonstrated using standard diode-side-pumped Nd:YAG modules. The laser produced 30 W of output power with beam quality factor M2<1.15 over the entire range of input powers and beam quality of 1.02 at the laser operation point. This is, to our knowledge, the highest beam quality for a dynamically stable high-power laser that uses an optically isotropic crystal. The laser was used as a pump source for an optical parametric oscillator based on a periodically poled lithium niobate, producing wavelength in the 1.5-3.8 µm range.

Dynamic random lasing in silica aerogel doped with rhodamine 6G.

Silica aerogel is a lightweight material, well known for its good mechanical and thermal characteristics, but its optical properties have received less attention, because it is weakly scattering. Here we present for the first time the lasing properties and their complex dynamics of silica aerogel doped with R6G. It is shown that the Q factors of the lasing modes determine the operation of the laser, being either resonant or ASE-lasing. For resonant lasing, the number of resonators is easily varied and the number of modes in a single resonator and their emission frequency can be dynamically adjusted, making this a truly versatile photonics material.

Large area resonant feedback random lasers based on dye-doped biopolymer films.

We report resonant feedback random lasing from dye-doped biopolymer films, consisting of a deoxyribonucleic acid-cetyltrimethylammonium (DNA-CTMA) complex doped with DCM dye. In the proposed devices, the optical feedback for random lasing is given by scattering centers randomly positioned along the edges of the active area. Scattering elements are either titanium dioxide nanoparticles or random defects at the interface between active polymer and air. Different emission spectra are observed, depending on the geometry of the excited area. A single random resonator with dimensions of 2.6 mm x 0.65 mm is fabricated and random emission with resonant feedback is obtained by uniformly pumping the full device.

Upconversion luminescence and decay kinetics in a diode-pumped nanocrystalline Nd3+:YVO4 random laser.

Random lasing in nanocrystalline Nd(3+):YVO(4) powder is demonstrated. A method that analyzes the decay kinetics after long-pulse excitation is used to determine the laser characteristics. This method permits to measure the fractional contribution of spontaneous and stimulated emission as well as upconversion as a function of the pump intensity. We observed that maximum linewidth narrowing is achieved when the stimulated emission reaches 50% of fractional contribution in the backscattering cone.

Effective transmission of light for media culture, plates and tubes.

The results of many investigations on low-level laser therapy are contradictory and this is due to the large number of illumination parameters as well as the inability to measure the possible effects after irradiation with the necessary objectivity and the fact that the light needs to pass thorough barriers (usually the plastic of the culture dish/plate and culture medium) to reach the cells. In this manner, the objective of this study was to determine the absorption coefficient, penetration depth and effective transmission in materials commonly used in cell cultures. Among the most commonly used wavelengths in low-level laser therapy, the lowest absorption coefficients were reached by DMEM and RPMI (α = 0.03 cm(-1)), from 633 to 690 nm, which reach an effective transmission of 93% of incident radiation and penetration depth of 33 cm. Among the solid materials in the same range of the electromagnetic spectrum, the lowest absorption coefficient was obtained for the polystyrene (Petri dish and well plate), with α = 1.31 cm(-1), 78% of effective transmission and 0.76 cm of penetration depth. This article also presents a simple equation for estimating the amount of energy that will actually reach the sample.

Continuous-wave Watt-level Nd:YLF/KGW Raman laser operating at near-IR, yellow and lime-green wavelengths.

A Nd:YLF/KGW Raman laser has been investigated in this work. We have demonstrated CW output powers at six different wavelengths, 1147 nm (0.70 W), 1163 nm (0.95 W), 549 nm (0.65 W), 552 nm (1.90 W), 573 nm (0.60 W) and 581 nm (1.10 W), with higher peak powers achieved under quasi-CW operation. Raman conversion of the 1053 nm fundamental emission is reported for the first time, enabling two new wavelengths in crystalline Raman lasers, 549 nm and 552 nm. The weak thermal lensing associated with Nd:YLF has enabled to achieve good beam quality, M(2) ≤ 2.0, and stable operation in relatively long cavities.

Low-level laser therapy in burning mouth syndrome patients: a pilot study.

OBJECTIVE: The aim of this study was to investigate the effect of low-level laser therapy (LLLT) on the treatment of burning mouth syndrome (BMS). In addition, the laser effect was compared on the different affected oral sites. MATERIALS AND METHODS: Eleven subjects with a total of 25 sites (tongue, lower lip, upper lip, and palate) affected by a burning sensation were selected. The affected areas were irradiated once a week for three consecutive weeks with an infrared laser (λ = 790 nm). The probe was kept in contact with the tissue, and the mucosal surface was scanned during the irradiation. The exposure time was calculated based on the fluence of 6 J/cm(2), the output power of 120 mW, and the area to be treated. Burning intensity was recorded through a visual analog scale before and after the treatment and at the 6-week follow-up. The percentage of the improvement in symptoms was also obtained. RESULTS: Burning intensity at the end of the laser therapy was statistically lower than at the beginning (p < 0.01). Patients reported an 80.4% reduction in the intensity of symptoms after laser treatment. There was no statistical difference between the end of the treatment and the 6-week follow-up, except for the tongue site. CONCLUSION: Under the investigated parameters, infrared LLLT proved to be a valuable alternative for BMS treatment, providing a significant and lasting reduction in symptoms.

Compact, diode-side-pumped Nd3+:YLiF4 laser at 1053 nm with 45% efficiency and diffraction- limited quality by mode controlling.

We demonstrate what we believe to be the highest efficiency obtained to date in a transversely diode-pumped Nd3+:YLiF4 slab laser operating at 1053 nm. The compact 11-cm-long laser cavity configuration is based on total internal reflection of the intracavity beam at the pump facet of the gain crystal to improve the overlap with the pump radiation. Multimode operation with 9.5 W of output power and an efficiency of 45% is obtained for 21 W of pump power in a single-pass configuration. Using a second pass through the crystal and a new mode-controlling technique, the beam quality is improved to the diffraction limit with 6.9 W of output power and 33% of optical-to-optical efficiency.

Color differences of canines and incisors in a comparative long-term clinical trial of three bleaching systems.

This study was a long-term clinical trial of home and in-office LED and laser bleaching systems comparing for the first time interdental color differences (differences between the central labial surfaces of the canine and the central incisor). A total of 90 patients were divided into three groups of 30 each. One group received day guard vital bleaching, and the other two groups received one bleaching session for 20 min accelerated by a diode laser for 30 s per tooth or a blue LED for 3 min per tooth, and both groups received additionally day guard for 7 days. A total of four color measurements were carried out during the study period of 3 months and 3 weeks. The group treated with the LED tended to show the highest degree of equalization of lightness, chroma and hue. A significantly stronger overall increase in lightness was observed for canines after treatment when compared with incisors resulting in more homogeneous lightness values.

Estudo in vivo sobre a influência das diferentes técnicas de clareamento na cor dental / In vivo study of the influence of different bleaching techniques on tooth color

Este estudo compara a efetividade do clareamento caseiro, associado ou não ao clareamento de consultório, com aceleração por LED ou por LASER. Participaram da pesquisa 92 pacientes distribuídos em três grupos: grupo A, uma sessão em consultório (LED) + clareamento caseiro (uma semana); grupo B, uma sessão em consultório (diodo LASER 808nm) + clareamento caseiro (uma semana); e grupo C: clareamento caseiro (duas semanas). Quatro medidas de cor foram realizadas com um espectrofotômetro portátil: 1) inicial; 2) imediatamente após a sessão em consultório (somente grupos A e B); 3) após pausa para retorno da cor (sete dias); e 4) pós-operatório de três meses. Os resultados revelam aumento no importante fator luminosidade L* nas medidas de cor 2, 3 e 4, em comparação com a medida 1 (inicial), para todos os grupos (variações ?L* entre as medidas para grupo A: med4 – med1= 2,3577; grupo B: med4 – med1= 1,6541; grupo C: med4 – med1= 3,6063). Na medida 3, esse aumento ocorreu para todos os grupos e não houve diferença estatística entre eles. Entretanto, após três meses, a manutenção dos resultados foi melhor para o grupo C, clareamento caseiro.

Dental bleaching efficacy with diode laser and LED irradiation: an in vitro study.

BACKGROUND AND OBJECTIVES: Bleaching techniques achieved significant advances with the use of coherent or incoherent radiation sources to activate the bleaching agents. This in vitro study compares the whitening efficacy of LED and diode laser irradiation using the two agents Opalescence X-tra and HP Whiteness. STUDY DESIGN/MATERIALS AND METHODS: A total of 60 bovine incisors were randomly divided into six groups, three for each bleaching agent, receiving only agent, agent and LED (wavelength 470 nm), agent and 1.6 W diode laser (808 nm). The results of the irradiations were characterized using the CIEL*a*b* system. RESULTS: Significant differences in the chroma value are obtained for the two whitening agents and for the different light sources. In terms of lightness, the association of Laser and Whiteness HP bleaching gel showed significantly better results than when the same agent was used alone or in combination with LED. CONCLUSIONS: Best overall results are obtained with the Whiteness HP and Laser association.

Bleaching efficacy of whitening agents activated by xenon lamp and 960-nm diode radiation.

OBJECTIVE: This in vitro study examines the efficacy of two different dental whitening agents, Opalescence Xtra and Opus White, by analyzing the change in color achieved by the treatment and the temperature increase induced in the pulpal chamber. BACKGROUND DATA: Bleaching techniques achieved significant advances with the use of coherent or incoherent radiation sources to activate the bleaching chemicals. METHODS: The bleaching agents, containing 35% of hydrogen peroxide, were stimulated with 0.9 W of xenon arc lamp and 0.9 W or 2 W of a 960-nm diode laser during 60 sec (0.9 W) and 30 sec (2 W) on 33 extracted human teeth. During irradiation, the temperature in the pulpal cavity was monitored. The color change was evaluated using the CIE L*a*b* color space measurement system. RESULTS: The treated groups showed an increase in color saturation (DeltaC*) of 3-32% and a change in whiteness (DeltaL*) of 0-8%. This study found that only some of the irradiated groups show statistically significant difference (p < 0.05) in the effectiveness of their treatment when compared to the control, whereas no significant statistical difference was obtained in between the irradiated groups. Temperature increase was 2-4 degrees C when using the xenon arc lamp, 2-8 degrees C and 4-12 degrees C when using the diode laser at 0.9 W and 2 W, respectively. CONCLUSIONS: The results of this study suggest that Opalescence Extra and Opus White are both effective to provide brighter teeth. However, according to the conditions used in this study, only the xenon arc lamp induced a safer temperature increase.