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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.

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

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.

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.

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.

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.

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.

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.