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Laser-induced wavefront distortion is detectable by several techniques based on the photothermal effect. The effect is probed by monitoring the phase shift caused by the bulging of the heated area, the photoelastic effects, and the spatial distribution of the refractive index within the sample and in the fluid surrounding it. A simple analytical solution for the wavefront distortion was only possible for low absorbing materials, with the assumption that the stresses obey either the thin-disk or the long-rod type distributions. Recently, a unified theoretical description for the laser-induced optical path change was proposed to overcome part of this limitation for weakly absorbing materials, regardless of its thickness. In this work, we perform an experimental investigation taking the sample–fluid heat coupling effect into account using the thermal lens technique. The experimental investigation presented here validates the unified model. In addition, we show that the heat-coupling model provides an alternative method to obtain physical properties of non-absorbing fluid by using a reference solid sample.

The mode-mismatched dual-beam thermal lens technique is widely applied in the characterization of optical and thermo-physical properties of solids and liquids. The technique has also been used to investigate transient acoustic waves induced by pulsed laser excitation at the nanosecond time scale. In this paper, we developed a semi-analytical model to describe the transient acoustic wave that allows a fitting procedure to get the physical properties of fluid samples. The method was used to investigate samples with different mixtures of ethanol and water, and quantitative information of piezo-optic coefficient and sound speed are evaluated for the fluid mixtures.

The cover glass in a silicon solar panel accounts for about 2/3 of the device's weight. Recycling these devices at their end-of-life is fundamental to reducing the industry's environmental impact. Here we investigate the recovery of these glass sheets by a heat-assisted mechanical process. A panel was delaminated, and we have utilized Fourier-transform infrared, Raman, and energy-dispersive spectroscopies to confirm the composition of the remaining components and identify aging signals. The results demonstrate that the panel's design was similar to most Silicon solar panels in the market, and we concluded that it would be feasible to recover the glass in most of these devices. Due to its chemical and mechanical strength, this glass would be ready to be reused without the need to melt it again, bringing substantial savings in its energy content and carbon emission related to its production. The glass sheet would be ready to be used as cover glass in another solar panel or architecture material. Our estimates showed that this could be a pathway to reducing the photovoltaic industry's carbon emissions by more than 2 million tonnes per year., Comment: 11 pages, 5 figures

One of the most significant materials in a solar panel is the glass, which provides transparency, UV protection as well as mechanical and chemical resistance. In this work, we describe the production of prototypes of four solar modules made using borosilicate, zinc-tellurite, Pr$^{3+}$ doped zinc-tellurite, and float glass as cover materials. The performance of these prototypes was evaluated under a solar simulator, and a device was developed to monitor all prototypes under real conditions. A comparison between indoor and outdoor measurements shows that outdoor results are fundamental to evaluate the performance of modified solar modules as the ones considered in this study. In addition, we demonstrate the fundamental role played by the refractive index of cover glasses in the performance of the prototypes, and discuss how this feature could be explored to achieve enhanced devices, as well as other benefits that may arise from this field of research., Comment: 6 pages, 3 figures

The demand for electricity and the need to replace fossil fuels by renewables have been growing steadily, and this transition will have significant implications to our world that are only beginning to be understood. Brazil is one important example of a big economy where the electricity is already supplied by renewables, such as hydro, wind and biomass-fired thermal power. In this work we investigated the electricity load curves in the last 20 years in Brazil, and four different scenarios for 2030 are proposed in order to evaluate the impact of increasing renewables in the national grid, at an hourly basis. The analysis shows that growing electricity demand and the expected reduction in the hydropower share will significantly increase the reliability of the national grid, due to higher peak load and also due to the intermittency of Solar and Wind. Without any gigawatt scale hydropower projected for the near future, increasing the share of these renewables should push hydropower to operate hundreds of hours every year above typical peak power levels experienced in the past. In order to avoid or reduce the threat related to this trend one of our scenarios suggests that solar water heaters could be massively deployed in Brazil, what would positively impact the system reliability by reducing the electricity demand mostly at peak loads during early evenings., 17 pages, 6 figures

This work aimed to investigate and compare the composition and the physicochemical properties of 18 different sources of edible vegetable oils. A systematic study on the correlation between composition and physical properties was performed using Fourier Transform Infrared (FTIR) Spectroscopy and fatty acid chromatographic analysis. Principal component analysis of FTIR spectra is performed to classify edible oils concerning their physical properties. The results demonstrate the potentiality of the method associated with multivariate statistics analysis as powerful, fast, and non-destructive tools for characterization and quality control of edible vegetable oils.

We use the thermal lens technique in the nanosecond time scale to describe the acoustic wave effect in liquids and the corresponding correlation with the speed of sound in the fluid, volumetric thermal expansion, and piezo-optic coefficient. These physical properties are found to be directly correlated to the anomalous effects observed in the transients at the nanosecond time scale, where acoustic waves dominate the thermal lens signal inducing an oscillating transient. Our results suggest the application of the thermal lens to study the generation and the detection of thermo-acoustic waves in liquids, which makes this method interesting for all-optoacoustic ultrasound detection and imaging.

Efficient white-emitting phosphor-in-glass (PiG) was successfully synthesized by synergistic complexation of Ce3+-doped YAG phosphor and Eu 3 + -doped sodium calcium silicate glass. The crystalline phosphor was obtained via sol-gel route using polyvinyl alcohol (PVA), whereas glasses were prepared by melting-quenching method. Rare-earth ions were successfully incorporated into the YAG and glass host lattices without changing their original structures. Through adjusting the Eu3+-doped glass and Ce3+:YAG phosphorus contents in the PiG, it was possible to optimize the chromaticity emission from yellow-green to orange-red in CIE 1931 diagram. Combination of a violet LED and samples emissions, allowed to achieve the chromaticity parameters closer to an ideal white light source [CIE-(0.33, 0.33); CCT 5000K]. Moreover, adjusting the luminescence intensity ratio between the LED and the PiG emission provides a tuning route for smart white light devices.

Fundamental studies of light-matter interactions are important for basic knowledge and in applications. Thanks to advances in experimental and theoretical methods, nowadays it is possible to perform such studies in a broad dynamic range, covering timescales from that of elementary interactions to real time. In the present work, we perform an experimental-theoretical study of light intensity-dependent femtosecond and CW-laser induced frequency upconversion in hierarchically structured core-multishell nanoparticles co-doped with NdIII, YbIII, and ErIII. Upconversion spectra recorded with CW and femtosecond excitation are qualitatively similar whereas the intensity dependence of upconversion depends on excitation mode (CW or femtosecond). To further assess the observed intensity dependence, we perform light-matter interaction simulations in the dynamic range from 100 fs to 3 ms for 18-level system describing the UCNPs, including nine levels of the NdIII, two of the YbIII, and seven of the ErIII ions and a classical model for the excitation source. The calculated time- and intensity-dependent energy level population are compared with measured spectra to understand CW vs femtosecond laser-induced upconversion. To further discuss the differences between CW and femtosecond laser-induced light-matter interactions for the systems studied here, we perform semi-classical pulse propagation simulations and ultrafast pump-probe measurements to study how the light source bandwidth, relative to the absorption linewidth, influence light absorption and transmission and further connect these results with the intensity dependence. Overall, we report our progress toward mechanistic studies of light-matter interaction and photophysical pathways following femtosecond excitation and UCNPs.

Emerging technologies are demanding innovative properties of glasses. In this work Cerium Oxide is used as dopant in Zinc-Tellurite samples and its effects on the properties of the glass are investigated. Thermal analysis and X-ray diffraction confirmed the amorphous nature of all samples. The bivalent nature of Cerium is investigated spectroscopically and an strong redshift induced by the dopant is attributed to charge transfers O 2 − → Ce 4 + , while the 4f-5d transition of Ce 3 + could not be identified in absorption or luminescence measurements. Yellow/red (570/650 nm) emission under 410/450 nm pumping were observed and are originated from Te 4 + ions, which absorbs light in the UV/blue region of the spectrum. The incorporation of some Cerium Oxide enhanced the visible luminescence, though we found no evidence that Cerium ions play some role in the radiative process. The luminescence is enhanced though due changes in the glass network induced by the dopant.

We demonstrate the influence of edge effects on the photothermal-induced phase shift measured by a homodyne quadrature laser interferometer and compare the experiments with rigorous theoretical descriptions of thermoelastic surface displacement of metals. The finite geometry of the samples is crucial in determining how the temperature is distributed across the material and how this affects the interferometer phase shift measurements. The optical path change due to the surface thermoelastic deformation and thermal lens in the surrounding air is decoded from the interferometric signal using analytical and numerical tools. The boundary/edge effects are found to be relevant to properly describe the interferometric signals. The tools developed in this study provide a framework for the study of finite size effects in heat transport in opaque materials and are applicable to describe not only the phase shift sensed by the interferometer but also to contribute to the photothermal-based technologies employing similar detection mechanisms. Prikažemo vpliv robnih učinkov na fototermalno inducirani fazni premik, ki ga merimo s homodinskim kvadraturnim laserskim interferometrom in poskuse primerjamo z eksaktnimi teoretičnimi opisi termoelastičnih površinskih premikov kovin. Končna geometrija vzorcev je ključnega pomena pri določanju, kako se temperatura porazdeli po materialu in kako to vpliva na merjenje faznega premika interferometra. Razliko optične poti zaradi površinske termoelastične deformacije in termalne leče v okoliškem zraku dekodiramo iz interferometričnega signala s pomočjo analitičnih in numeričnih orodij. Mejni/robni učinki so pomembni za pravilen opis interferometričnih signalov. Orodja, razvita v tej študiji, nudijo okvir za preučevanje učinkov zaradi končnih dimenzij pri prenosu toplote v neprozornih materialih in niso uporabna le za opisovanje faznega premika, ki ga zazna interferometer, temveč prispevajo tudi k fototermalnim tehnologijam, ki uporabljajo podobne mehanizme zaznavanja.

The development of enhanced optical devices relies on key materials properties. In this context, researchers have investigated the effects of metal nanoparticles incorporation in active rare-earth materials. Here, we discuss the effects of Silver nitrate addition (0.5%, 1.0% and 2.0% mol%) into P r 3 + doped tellurite-tungstate glasses (TWNN) formed by the conventional melt-quenching technique. We verified some improvement in thermal stability due Ag addition. In the absorption spectra the presence of a broadband around 500 nm indicates the presence of surface plasma resonance (SPR). By analysing the emission spectra, we have seen that at high codopant concentration the symmetry of P r 3 + site is being affected. Finally, by measuring the D 2 1 and P 0 3 lifetimes and the refractive index for samples annealed between 10 min and 20 h about ∼ 50 ° C below the glass transition temperature, we confirmed that some dynamics is taking place. The main possibility is that NPs keep growing at such temperature, affecting the polarizability and site symmetry. P r 3 + doped TWNN glass can have some transitions enhanced by the codoping scheme investigate here, as well some improvement in thermal stability. However, when fabricating a real device any additional annealing or even the temperature during operation may play a role in its performance.

Resumo Neste trabalho apresento uma abordagem revisada do Spin para um curso introdutório de física moderna. Essa proposta é elaborada considerando o ponto de vista de que habitualmente o Spin é apresentado como um “objeto estranho”; ele sugere aos alunos que os elétrons estão girando basicamente no mesmo instante em que os alunos são apresentados a mecânica ondulatória, onde partículas clássicas não existem mais. Aqui, busco apresentar o Spin respeitando a ordem cronológica de sua concepção, discutindo os artigos originais e o que pensaram os principais autores que coletivamente contribuiram para a teoria. Paralelamente, isso é feito contextualizando a importância tecnológica que o Spin desempenha em nossa sociedade. Abstract In this work I present an revised approach to the Spin for an introductory course of modern physics. This proposal is elaborated considering the point of view that oftenly the Spin is presented as a “strange object”; it suggests to the students that electrons are spinning basically in the same instant that those students are presented to ondulatory mechanics, where classical particles no longer exists. Here, I look for present the Spin regarding the cronological order as it was conceived, discussing the original articles and what though the main authors that collectivelly contributed to the theory. At the same time, this is made contextualizing the technological importance that is played by the Spin in our society.

We propose a combined pump-probe optical method to investigate heat diffusion properties of solids. We demonstrate single-shot simultaneous laser-induced thermoelastic surface displacement of metals detected by concurrent measurements using photothermal mirror and interferometry. Both methods probe the surface displacement by analyzing the wavefront distortions of the probe beams reflected from the surface of the sample. Thermoelastic properties are retrieved by transient analysis in combination with numerical description of the thermoelastic displacement and temperature rise in the sample and in the surrounding air. This technique presents a capability for material characterization that can be extended to experiments for quantitative surface mapping.

A study of the broadband near-infrared emission in Pr3+ single doped and Pr3+/Yb3+ codoped tellurite–tungstate glasses for optical amplification is presented. In the Pr3+ single doped samples pumped at 474 nm the emission band at 1480 nm presents a FWHM of ∼140 nm. The Yb3+ addition produces a FWHM broadening up to ∼155 nm, achieved through the 1G4–3H5 transition. The emission spectra when the codoped sample is pumped at 980 nm shows efficient energy transfer from Yb3+ to Pr3+, resulting in an intense Pr3+ emission around 1330 nm. This shows that changing the pump wavelength it is possible to select the 1D2–1G4 or the 1G4–3H5 transition, displacing the emission band from ∼1480 to ∼1330 nm.

Spectral converters are known to increase photovoltaic energy conversion by minimizing losses due to fundamental non-absorption and thermalization processes, and have been suggested to surpass the Shockley-Queisser efficiency limit in single junction solar cells. Here we present a detailed spectroscopic study of photoluminescence in tellurite-tungstate glasses doped and codoped with P r 3 + − Y b 3 + and Ag nanoparticles. The energy transfer mechanisms between P r 3 + and Y b 3 + are discussed based on the near infrared emission under excitation at 442 nm and on the upconversion emission under excitation at 980 nm. Fluorescence quenching of 2F5/2 level of Y b 3 + is observed by increasing the concentration of P r 3 + , as well as by the addition of Ag nanoparticles. In addition, a discussion on the potential of this glass to increase energy production in spectral converters is presented. The results suggest that the few undesirable energy transfer processes occurring in this material are difficult to be controlled or eliminated properly, resulting in intrinsic losses. This discussion is extended to the potential of glass science to enhance energy production in solar cells, showing that newer designs such as bifacial cells may facilitate the exploration of glasses other than soda-lime for mass production of solar cells. The focus on extending the lifespan by reducing UV induced degradation seems to be a more effective approach than the development of spectral converters for Si solar cells.

In this work we present our findings performing low frequency Raman measurements over temperature in a tellurite-tungstate glass sample. The spectra could be fitted by using only two log-Gaussians, which suggests that quasi-elastic light scattering is negligible. The positions of the peaks have the same temperature behavior, being the higher frequency one refereed as Boson Peak in literature. The similar temperature behavior and depolarization ratio indicates that the peaks may have the same origin, being linked to the transversal and longitudinal vibrations of some unit.

Ce:Y 3 Al 5 O 12 and Eu:Y 3 Al 5 O 12 ceramics were obtained by combining high-energy ball milling and inert-gas flow sintering. The photoluminescence properties of Ce:Y 3 Al 5 O 12 ceramics were identical to those reported for Ce:Y 3 Al 5 O 12 single crystals, while the Eu:Y 3 Al 5 O 12 luminescence spectra were attributed to a larger concentration of Eu 2+ in relation to Eu 3+ ions as a direct consequence of the synthesis protocol. The Eu:Y 3 Al 5 O 12 photoluminescence emission and excitation spectra are very similar to those of Ce:Y 3 Al 5 O 12 , attesting the feasibility for applying Eu 2+ :Y 3 Al 5 O 12 ceramics as white-light phosphors.

We investigate the dynamics of many interacting bubbles in boiling water by using a laser scattering experiment. Specifically, we analyze the temporal variations of a laser intensity signal which passed through a sample of boiling water. Our empirical results indicate that the return interval distribution of the laser signal does not follow an exponential distribution; contrariwise, a heavy-tailed distribution has been found. Additionally, we compare the experimental results with those obtained from a minimalist phenomenological model, finding a good agreement., Comment: Accepted for publication in Chaos, Solitons & Fractals

Thulium doped Samarium codoped tellurite-tungstate glasses were produced. Luminescence properties in the infrared region were investigated looking to observe improved properties for S-band amplification in the co doped samples. Thulium is well-known by the 3 H 4 - 3 F 4 radiative transition emitting around ~1.47μm, which is a self-terminating transition in tellurite hosts due the longer lifetime of the lower level in relation to the upper level of this transition. Analysis of absorption and emission spectra showed that we could quench the 3F4 level significantly, what improved the intensity of the emission at 1.49μm. However, the state 3 H 4 were also quenched due the cross relaxation process due the absorption bands of Sm 3+ around 1.5μm.

Tellurite glasses following the molar concentration 71.5% TeO2, 22.5% WO3, 5% Na2O and 1.5% Nb2O5 have been investigated. Samples doped with Tm2O3, Pr2O3, Yb2O3 or Bi2O3 were fabricated by the conventional melt quenching process. Rare-earth (RE) 3+ ions have well defined emission bands. On the other hand, Bismuth emission in the infrared region have been found in some glasses and even that emission laser have been already obtained, the mechanism behind its luminescence is still misunderstood[1]. The Bismuth emission is sometimes referred as a “superbroadband” emission around 1.3um, which is very promising for an optical amplifier, but, to the best of our knowledge a bismuth based optical amplifier have not been produced yet. Our purpose is to investigate the mechanism behind this misunderstood “superbroadband” luminescence, and compare it with the rare-earths properties in the same range. The characterization consists in measurements of optical absorption spectra, optical emission spectra and life-time decay. Differential thermal analysis (DTA) was also performed, to identify changes in T g and T x as function of the doping concentration, which is important to the drawing process of a fiber.

We present experimental results of optical amplification by using Er3+-doped tellurite MOFs. Also, a study of broadband near infrared emission in Pr3+ single-doped and Pr3+/Yb3+ codoped tellurite-tungstate glasses to perform new MOFs is presented.

Energy transfer processes in Yb3+-Tb3+ co-doped, low-silica calcium aluminosilicate glasses were analyzed. Luminescence and time-resolved measurements were used to study upconversion processes, such as Yb-Tb cooperative sensitization, Yb-Yb cooperative luminescence, and Yb-Tb cross relaxation. The quantum cross relaxation efficiency was evaluated as a function on the Yb3+ concentration, and the maximum estimated value was approximately 51%. In addition, the intensity of the upconversion luminescence from the Tb3+:5D4 level decreased by two orders of magnitude comparing the value at room temperature with that at 123 K. As a consequence, Yb-Yb cooperative luminescence around 500 nm became comparable with the intensity of upconversion from the Tb3+:5D4 level. Furthermore, a dependence of the upconversion kinetics luminescence on temperature was observed. The upconversion rise time was constant and equal to 65 μs for temperatures between 296 to 473 K and decreased from 65 to 19 μs, without variation in the decay part, when the temperature was lowered from 296 to 123 K. These results were explained by a phonon-assisted cooperative sensitization process for the population of the Tb3+:5D4 level.

“Calcium aluminosilicate” (CAS) and “low silica calcium aluminosilicate” (LSCAS) OH− free glasses have demonstrated a good potential for solid-state laser media and luminophore hosts due to good thermal, optical, and mechanical properties. Some examples have already been shown with Nd3+, Er3+, Ce3+, and Ti3+ luminescent ions. In this work, Yb3+ rare-earth laser ions have been introduced into the two series of CAS and LSCAS glasses melted at 1600 °C in a vacuum furnace and have been optically characterized and compared. Special attention has been devoted to both structural characterization in relationship with spectroscopic properties and concentration quenching phenomenon in relationship with laser parameters. Laser measurements at 1037 nm have been successfully performed under laser diode pumping.

The finite-size effect on the thermal mirror (TM) experiments is described. The time-resolved thermoelastic deformation equation is solved and compared to the semi-infinite solution. To determine the applicability of the semi-infinite model, experiments were performed in optical glasses and the quantitative results compared to both models. The analytical results presented here were found to be in excellent agreement with the numerical finite elemental analysis model. Modeling and experiment showed that the TM transient signal is strongly affected as the sample thickness is reduced. The results of the finite-size model demonstrate that it is intrinsically more accurate to characterize physical properties of low optical absorption thin samples, which suggests that the model and the TM method could even be applied to study very thin films down to the micrometer scale.

Analytical and finite element analysis modeling methods of the pulsed-laser excited photothermal (PT) lens signal of solids samples surrounded by air are presented. The analytical and finite element analysis solutions for the temperatures induced in the sample and in the air were found to agree over the range of conditions in this report. Model results show that the air contribution to the total PT lens signal is significant in many cases. In fact, these solutions open up the possibility of applying the pulsed excited thermal lens method for accurate prediction of the heat transfer to the coupling fluid and subsequently to study the gas surrounding the samples by using a known material solid sample.

The mode-mismatched thermal lens technique(TL) has been used to study many semitransparent materials. Its theoretical development considers weakly absorbing materials, which introduce restrictions on the sample's optical thickness. However, the same equipment required by TL can be used to perform the thermal mirror (TM) experiment, which is useful to characterize materials with any optical absorption coefficient. In this work, we investigate a simple correction to be used in the TL model, making it possible to apply TL to a wide range of materials. Using TL and TM, we have determined the temperature coefficient of the optical path length (ds/dT) of a glass.

A general and complete theoretical model of the time-resolved thermal mirror method for the measurement of thermo-optical-mechanical properties of solid materials is developed. The laser-induced temperature profile in a sample and its thermoelastic surface displacement are derived. The center intensity of a probe beam at the detector plane is calculated using the Fresnel diffraction theory. Additionally, simplified models for high and low optical absorption samples are presented, and the suitability of the simplified models is also analyzed. The influence of experimental parameters on the sensitivity of the thermal mirror method is discussed for the optimization of the experimental apparatus. The presented model and the experimental technique can be used to quantitatively determine the physical properties of transparent and opaque solids.

Nesta carta apresento o meu ponto de vista sobre o importante papel da contextualização da física e seus desdobramentos na sociedade no ensino de física. Aponto meu questionamento sobre a real origem de disciplinas como “ciência, tecnologia e sociedade”(CTS) e “alfabetização científica e tecnológica”(ACT), argumentando que talvez se deva discutir a estrutura do ensino de física ao invés de “acrescentar” uma etapa que visa corrigir a lacuna que criamos entre a física e a sociedade. Muitos teóricos tem resgatado que CTS e ACT nasceram de um ponto de vista Freiriano sobre o ensino, entretanto o que vemos na prática é a insistência no método e em bibliográfias mais velhas do que este movimento pedagógico.

When electromagnetic waves go through materials different effects may occur depending upon the physical properties of the materials. One of them is of great interest for the analysis of thermal-optical properties and it is known as the photothermal effect. The thermal lens techniques bases is this effect and since its discovery the thermal lens became a powerful tool to describe the thermal-optical properties of huge number of materials, whether liquids or solids. However, no matter how detailed, all the model that have emerged over the years always considered that the excitation beam radius didnt change throughout the sample. In order to verify this condition, we developed a thermal lens mismatched-mode model that consider an azimuthal dependence for the laser radius. Obtaining the intensity expression allowed us to perform a lot of computational analysis and also allowed us to compare this analysis with experimental data. We concluded that the constant radius consideration is valid only if the ratio between the confocal distance and the thickness of the sample is sufficiently large, in other words, the confocal distance must be larger than the samples thickness, otherwise the presented model must be Quando uma onda eletromagnética incide sobre um dado material diversos efeitos podem ocorrer dependendo das propriedades físicas deste material. Um deles é de grande interesse para as análises das propriedades ópticas e térmicas, e é conhecido como efeito fototérmico. A base da técnica de lente térmica (LT) consiste neste efeito e desde a sua descoberta a lente térmica se tornou uma poderosa ferramenta para a descrição de propriedades termo-ópticas de uma grande quantidade de materiais, sejam eles líquidos ou sólidos. Entretanto, por mais abrangente que fosse, todos os modelos que surgiram ao longo dos anos sempre partiam do pressuposto de que o raio do feixe do laser não variava ao atravessar a amostra. Afim de verificar a validade de considerarmos esta condição, desenvolvemos aqui um modelo para o modo descasado que considera uma dependência azimutal no raio do feixe de excitação. A obtenção da expressão de intensidade nos permitiu realizar diversas simulações para verificar o nosso modelo e fazer uma comparação com dados obtidos experimentalmente. Concluímos que a consideração do raio constante ao atravessar a amostra é válida desde que a razão entre a distância confocal e a espessura da amostra seja suficientemente grande, ou seja, desde que a distância confocal seja maior do que a espessura da amostra. Do contrário o modelo proposto deve ser empregado para melhor descrever os parâmetros físicos da amostra ix, 66 f

Resonant excited-state absorption and relaxation processes in Tb3+-doped aluminosilicate glasses are quantitatively evaluated under UV excitation. A model describing the excitation steps and upconversion emission is developed and applied to interpret the results from laser-induced surface deformation using the thermal mirror spectroscopy. The fluorescence quantum efficiency of level 5D4 was found to be close to unit and concentration independent, while for the level 5D3 it decreases with Tb3+ concentration. Emission spectroscopy measurements supported these results. Excited-state absorption cross-sections are found to be more than two orders of magnitude higher than the ground-state absorption cross-section. Processos de relaxação e absorção de estado excitado em vidros aluminosilicato de cálcio dopados com Tb3+ são quantitativamente investigados sob excitação UV. Um modelo que descreve as excitações e as emissões "upconversion" é desenvolvido e aplicado para interpretar os resultados da deformação superficial induzida via laser pela Espectroscopia de Espelho Térmico. A eficiência quântica da fluorescência do nível 5D4 foi aproximadamente unitária e independente da concentração, enquanto que a do nível 5D3 decresceu com a concentração de Tb3+. Medidas de espectroscopia de emissão suportaram esses resultados. As seções de choque de absorção de estado excitado foram determinadas e apresentaram valores três ordens de magnitude maiores que a seção de choque de absorção do estado fundamental. x, 63 f

This work presents a theoretical and experimental study in Thermal Lens (TL) and Thermal Mirror (TM) techniques by taking sample-fluid heat coupling into account. The heat conduction equation is solved to obtain a semi-analytical solution to the temperature in the sample and in the surrounding fluid in the case of continuous and pulsed laser excitation. The thermoelastic equation is used to obtain the displacement induced on the sample surface. The solutions to the temperature and surface displacement, for samples with low optical absorption ( - ) and high optical absorption ( - ), are in excellent agreement with the results obtained using Finite Element Method (FEM). The solutions are used to model the TL and TM effects considering the contribution of the sample and the fluid. The heat transfer between the sample and the air coupling fluid does not introduce an important effect over the induced probe beam phase shift when compared to the solution obtained without considering axial heat flux, unless to extremely thin samples. However, when using water as the surrounding fluid, heat coupling led to a significant effect in fluid phase shift. Experimental results using stainless steel in air and water are used to demonstrate the potentiality of the TM technique to determine the thermal properties of both the sample and the fluid. A theoretical analysis of the pulse laser profile in the TM technique is presented. TM experiments performed in optical glasses show that the technique is useful for quantitative determination of the thermal diffusivity of materials with low optical absorption. Este trabalho apresenta um estudo teórico e experimental do efeito de acoplamento térmico entre amostra sólida e fluido adjacente nas técnicas de Lente Térmica (LT) e de Espelho Térmico (ET). A equação de difusão de calor é resolvida para obter uma solução semianalítica para a temperatura na amostra e no fluido considerando a excitação laser contínua e a pulsada. A equação termoelástica é utilizada para a obtenção da deformação induzida na superfície da amostra. As soluções para a temperatura e a deformação superficial, considerando amostras com baixa absorção óptica ( ) e com alta absorção óptica ( ), apresentam ótima concordância com os resultados obtidos por meio de Método de Elementos Finitos (MEF). As soluções são utilizadas para modelar os efeitos de LT e ET, considerando tanto a contribuição da amostra quanto a do fluido. Como resultado, verifica-se que a transferência de calor de uma amostra para o ar não expressa diferença relevante na mudança de fase do feixe de prova quando comparada com a solução sem fluxo de calor, a não ser no caso de amostras extremamente finas. Porém, quando a água é utilizada como fluido circundante à amostra, um efeito significante de mudança de fase surge no feixe de prova devido ao fluido. Resultados experimentais em aço inoxidável imerso em ar e em água são utilizados para demonstrar o potencial da técnica de ET para determinar as propriedades térmicas tanto da amostra quanto do fluido. Uma análise teórica do efeito da forma do pulso laser na técnica de ET é apresentada. Experimentos de ET em vidros ópticos mostram que a técnica é útil na determinação quantitativa da difusividade térmica de materiais com baixa absorção óptica. 102 f