Reviewing the effect of aggregates in Rhodamine 6G aqueous solution on fluorescence quantum efficiency.

Rhodamines constitute a class of dyes extensively investigated and applied in various contexts, primarily attributed to their high luminescence quantum yield. This study delves into the impact of aggregation on the thermal and optical properties of Rhodamine 6G (R-6G) solutions in distilled water. Examined properties encompass thermal diffusivity (D), temperature coefficient of the refractive index (dn/dT), fluorescence quantum efficiency (η), and energy transfer (ET). These parameters were assessed through thermal lens (TL) and conventional absorption and emission spectroscopic techniques. The dimerization of R-6G solutions was revisited, revealing that an increase in R-6G concentration alters the features of absorption and emission spectra due to dimer formation, resulting in unexpected behavior of η. Consequently, we introduce a novel model for the fraction of absorbed energy converted into heat (φ), which accounts for emissions from both monomers and dimers. Employing this model, we investigate and discuss the concentration-dependent behaviors of η for monomers (ηm) and dimers (ηd). Notably, our findings demonstrate that ηm values necessitate ηd = 0.2, a relatively substantial value that cannot be disregarded. Additionally, applying the Förster theory for dipole-dipole electric ET, we calculate microparameters for ET between monomers (CDD) and monomer-dimer (CDA). Critical ranges for ET in each case are quantified. Microparameter analysis indicates that ET between monomer-monomer and monomer-dimer species of R-6G dissolved in distilled water holds significance, particularly in determining ηm. These results bear significance, especially in scenarios involving high dye concentrations. While applicable to R-6G in water, similar assessments in other media featuring aggregates are encouraged.

Towards a comprehensive characterization of spatio-temporal dependence of light-induced electromagnetic forces in dielectric liquids.

The interaction of localized light with matter generates optical electrostriction within dielectric fluids, leading to a discernible change in the refractive index of the medium according to the excitation's light profile. This optical force holds critical significance in optical manipulation and plays a fundamental role in numerous photonic applications. In this study, we demonstrate the applicability of the pump-probe, photo-induced lensing (PIL) method to investigate optical electrostriction in various dielectric liquids. Notably, the thermal and nonlinear effects are observed to be temporally decoupled from the electrostriction effects, facilitating isolated observation of the latter. Our findings provide a comprehensive explanation of optical forces in the context of the recently introduced microscopic Ampère electromagnetic formalism, which is grounded in the dipolar approximation of electromagnetic sources within matter and characterizes electrostriction as an electromagnetic-induced stress within the medium. Here, the optical force density is re-obtained through a new Lagrangian approach.

Optical detection of the ultrasound-induced pulsed thermal lens close to the ice-water phase transition.

Piezo-optic and thermo-optic coefficients are important material properties that play a critical role in the design and optimization of many optical devices. The ability to accurately measure and control these coefficients is essential for achieving high performance and reliability in a wide range of applications. In this article, we use the optical detection of the ultrasound-induced thermal lens effect to investigate these properties for water at low temperatures. The results show that the anomalous behavior of water around 4°C is easily observed. The thermal lens method is used to determine the temperature dependence of the piezo-optic and thermo-optic coefficients.

The role of electrostriction in the generation of acoustic waves by optical forces in water.

We present semi-analytical solutions describing the spatiotemporal distributions of temperature and pressure inside low-absorbing dielectrics excited by tightly focused laser beams. These solutions are compared to measurements in water associated with variations of the local refractive index due to acoustic waves generated by electrostriction, heat deposition, and the Kerr effect at different temperatures. The experimental results exhibited an excellent agreement with the modeling predictions, with electrostriction being the dominant transient effect in the acoustic wave generation. Measurements at 4 . 0 ∘ C show that the thermoelastic contribution to the optical signal is significantly reduced due to the low thermal expansion coefficient of water at this temperature.

Unveiling bulk and surface radiation forces in a dielectric liquid.

Precise control over light-matter interactions is critical for many optical manipulation and material characterization methodologies, further playing a paramount role in a host of nanotechnology applications. Nonetheless, the fundamental aspects of interactions between electromagnetic fields and matter have yet to be established unequivocally in terms of an electromagnetic momentum density. Here, we use tightly focused pulsed laser beams to detect bulk and boundary optical forces in a dielectric fluid. From the optical convoluted signal, we decouple thermal and nonlinear optical effects from the radiation forces using a theoretical interpretation based on the Microscopic Ampère force density. It is shown, for the first time, that the time-dependent pressure distribution within the fluid chiefly originates from the electrostriction effects. Our results shed light on the contribution of optical forces to the surface displacements observed at the dielectric air-water interfaces, thus shedding light on the long-standing controversy surrounding the basic definition of electromagnetic momentum density in matter.

Laser induced thermoelastic surface displacement in solids detected simultaneously by photothermal mirror and interferometry.

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.

Investigation into photostability of soybean oils by thermal lens spectroscopy.

Assessment of photochemical stability is essential for evaluating quality and the shelf life of vegetable oils, which are very important aspects of marketing and human health. Most of conventional methods used to investigate oxidative stability requires long time experimental procedures with high consumption of chemical inputs for the preparation or extraction of sample compounds. In this work we propose a time-resolved thermal lens method to analyze photostability of edible oils by quantitative measurement of photoreaction cross-section. An all-numerical routine is employed to solve a complex theoretical problem involving photochemical reaction, thermal lens effect, and mass diffusion during local laser excitation. The photostability of pure oil and oils with natural and synthetic antioxidants is investigated. The thermal lens results are compared with those obtained by conventional methods, and a complete set of physical properties of the samples is presented.

Discriminating the role of sample length in thermal lensing of solids.

Thermal lens (TL) is a key effect in laser engineering and photothermal spectroscopy. The amplitude of the TL signal or its dioptric power is proportional to the optical path difference (OPD) between the center and border of the beam, which is proportional to the heat power (Ph). Due to thermally induced mechanical stress and bulging of end faces of the sample, OPD depends critically on the geometry of the sample. In this investigation, TL measurements were performed as a function of the sample length keeping the same Ph. It is experimentally demonstrated that for materials with positive ∂n/∂T OPD increases typically 30 to 50% with the decrease of sample length (from long rod to thin-disk geometry). For materials with negative ∂n/∂T, this variation is much larger due to the cancelation of the different contributions to OPD with opposite signs. Furthermore, the experimental investigation presented here validates a recently proposed unified theoretical description of the TL effect.

Role of photophysics processes in thermal lens spectroscopy of fluids: a theoretical study.

Photophysics processes are ubiquitous in nature and difficult to be quantitatively characterized by conventional spectroscopy. Alternatively, pump-probe methods have been widely applied to study these complex processes. In this context, the thermal lens technique is a precise spectroscopic tool for material characterization and presents a wide range of applications in chemical analysis. Here, we present an all numerical approach to analyze the dynamics of photophysics processes and to identify the role of individual contributions of photoreaction and mass diffusion in the thermal lens experiments. The results are essential for a proper understanding of the dominant physical mechanisms in laser-induced photodegradation, which allow precise data analysis of the effects in photosensitive fluids.

The phase-resolved photoacoustic method to indicate chemical assignments of paracetamol.

In this work, the phase-resolved photoacoustic method was applied to provide specific information on the chemical assignments of paracetamol in the near-infrared region. Two broad bands, centered at 1370 and 1130 nm, were well-resolved using this method, making it possible to assign the peaks centered at 1398, 1355 and 1295 nm to a C-H combination from a CH3 structure and the peak at 1305 nm to a C-H combination from the aromatic ring. This information represents a new finding in chemical studies regarding this medicament.

Pulsed photothermal mirror technique: characterization of opaque materials.

The time-resolved thermal mirror technique is developed under pulsed laser excitation for quantitative measurement of thermal and mechanical properties of opaque materials. Heat diffusion and thermoelastic equations are solved analytically for pulsed excitation assuming surface absorption and an instantaneous pulse. Analytical results for the temperature change and surface displacement in the sample are compared to all-numerical solutions using finite element method analysis accounting for the laser pulse width and sample geometry. Experiments are performed that validate the theoretical model and regression fitting is performed to obtain the thermal diffusivity and the linear thermal expansion coefficient of the samples. The values obtained for these properties are in agreement with literature data. The technique is shown to be useful for quantitative determinations of the physics properties of metals with high thermal diffusivity.

Resonant excited state absorption and relaxation mechanisms in Tb3+-doped calcium aluminosilicate glasses: an investigation by thermal mirror spectroscopy.

Resonant excited state absorption (ESA) and relaxation processes in Tb(3+)-doped aluminosilicate glasses are quantitatively evaluated. A model describing the excitation steps and upconversion emission is developed and applied to interpret the results from laser-induced surface deformation using thermal mirror spectroscopy. The fluorescence quantum efficiency of level (5)D(4) was found to be close to unity and concentration independent while, for the level (5)D(3), it decreases with Tb(3+) concentration. Emission spectroscopy measurements supported these results. ESA cross sections are found to be more than three orders of magnitude higher than the ground state absorption cross section.

Modeling the population lens effect in thermal lens spectrometry.

We report a theoretical model and experimental results for laser-induced lensing in solids. The model distinguishes and quantifies the contributions from population and thermal effects. Laser-induced lensing in ytterbium-doped fluorozirconate glass ZBLAN:Yb(3+) is measured, and the thermal and optical properties obtained from analyzing the data with the proposed model agree well with published values. Photothermal techniques are used extensively for the investigation of laser and laser-cooling materials, and the model developed here enables the interpretation of convoluted laser-induced lensing signals that have contributions from different sources.

Investigation of the photobleaching process of eosin Y in aqueous solution by thermal lens spectroscopy.

Eosin Y is known to be a powerful probe of biological molecules and an efficient photosensitizing agent for the production of singlet molecular oxygen. Under continuous laser excitation, degradation through photobleaching is observed in aqueous solutions of eosin Y; this process is driven by the production of singlet oxygen. Optical bleaching in aqueous solutions is known to yield anomalous thermal lens transient signals, which can be evaluated by modeling the relaxation processes that give rise to the generation of heat in the solution. A model describing photobleaching in the thermal lens transient signal is derived and is applied to investigate eosin Y in aqueous solutions at different temperatures. Using this model, quantitative information regarding the molecular diffusion rate, optical bleaching, and fluorescence quantum efficiency is obtained.

Laser-induced chemical reaction characterization in photosensitive aqueous solutions.

A dual-wavelength on/off-excitation thermal lens technique was used to identify and quantify a laser-induced chemical reaction in ionic aqueous solutions of Fe(II)-TPTZ. On/off modeling was used to fit the TL experimental data, which provided the primary effect generated during laser-excitation. The addition of HCl in the solutions reduced the activation barrier; this behavior followed the Arrhenius correlation. The nature of the photo-oxidation of Fe(II)-TPTZ complex is discussed. The results suggest that this technique may contribute to the understanding of the dynamics of complex reactions, which may lead to a more precise determination of the physicochemical properties involved in a photochemical reaction.

Thermo-optical characteristics and concentration quenching effects in Nd3+ doped yttrium calcium borate glasses.

In this work we present a comprehensive study of the spectroscopic and thermo-optical properties of a set of samples with composition xNd(2)O(3)-(5-x)Y(2)O(3-)40CaO-55B(2)O(3) (0 ≤ x ≤ 1.0 mol%). Their fluorescence quantum efficiency (η) values were determined using the thermal lens technique and the dependence on the ionic concentration was analyzed in terms of energy transfer processes, based on the Förster-Dexter model of multipolar ion-ion interactions. A maximum η = 0.54 was found to be substantially higher than for yttrium aluminoborate crystals and glasses with comparable Nd(3+) content. As for the thermo-optical properties of yttrium calcium borate, they are comparable to other well-known laser glasses. The obtained energy transfer microparameters and the weak dependence of η on the Nd(3+) concentration with a high optimum Nd(3+) concentration put this system as a strong candidate for photonics applications.

Soret effect and photochemical reaction in liquids with laser-induced local heating.

We report a theoretical model and experimental results for laser-induced local heating in liquids, and propose a method to detect and quantify the contributions of photochemical and Soret effects in several different situations. The time-dependent thermal and mass diffusion equations in the presence and absence of laser excitation are solved. The two effects can produce similar transients for the laser-on refractive index gradient, but very different laser-off behavior. The Soret effect, also called thermal diffusion, and photochemical reaction contributions in photochemically reacting aqueous Cr(VI)-diphenylcarbazide, Eosin Y, and Eosin Y-doped micellar solutions, are decoupled in this work. The extensive use of lasers in various optical techniques suggests that the results may have significance extending from physical-chemical to biological applications.

Color tunability with temperature and pump intensity in Yb3+/Tm3+ codoped aluminosilicate glass under anti-Stokes excitation.

Pump and thermally induced color tunabilities were demonstrated in Yb(3+)/Tm(3+) codoped low silica calcium aluminosilicate (LSCAS) glass under anti-Stokes excitation at 1.064 microm. The effects of pump intensity and sample's temperature on the upconversion emissions and mainly on the color tunabilities (from 800 to 480 nm) were investigated. The results revealed a 20- and a threefold reductions at 800/480 nm ratio as, respectively, the pump intensity and sample's temperature were increased from 27 to 700 kW/cm(2) and from 296 to 577 K. These behaviors with pump intensity and temperature (a strong increase of the 480 nm emission in comparison with the 800 nm one) were attributed to the several efficient processes occurring in the LSCAS system (Yb(3+)-->Tm(3+) energy-transfer processes, easy saturations of the Yb(3+) and Tm(3+) excited states, and radiative emissions). Besides these assigns, the temperature dependence is mainly assigned to the temperature-dependent effective absorption cross section of the ytterbium sensitizer through the so-called multiphonon-assisted anti-Stokes excitation process. Theoretical analyses and fits of the experimental data provided quantitative information.

Note: Determination of effective gas diffusion coefficients of stainless steel films with differently shaped holes using a Loschmidt diffusion cell.

In this work, an in-house made Loschmidt diffusion cell is used to measure the effective O(2)-N(2) diffusion coefficients through four porous samples of different simple pore structures. One-dimensional through-plane mass diffusion theory is applied to process the experimental data. It is found that both bulk diffusion coefficient and the effective gas diffusion coefficients of the samples can then be precisely determined, and the measured bulk one is in good agreement with the literature value. Numerical computation of three-dimensional mass diffusion through the samples is performed to calculate the effective gas diffusion coefficients. The comparison between the measured and calculated coefficient values shows that if the gas diffusion through a sample is dominated by one-dimensional diffusion, which is determined by the pore structure of the sample, these two values are consistent, and the sample can be used as a standard sample to test a gas diffusion measurement system.

Thermal lens and interferometric method for glass transition and thermo physical properties measurements in Nd2O3 doped sodium zincborate glass.

In this work the time resolved thermal lens method is combined with interferometric technique, the thermal relaxation calorimetry, photoluminescence and lifetime measurements to determine the thermo physical properties of Nd(2)O(3) doped sodium zincborate glass as a function of temperature up to the glass transition region. Thermal diffusivity, thermal conductivity, fluorescence quantum efficiency, linear thermal expansion coefficient and thermal coefficient of electronic polarizability were determined. In conclusion, the results showed the ability of thermal lens and interferometric methods to perform measurements very close to the phase transition region. These techniques provide absolute values for the measured physical quantities and are advantageous when low scan rates are required.