Mode-mismatched Thermal Lens Technique Research Articles

Determination of the Thermal Diffusivity of Plasmonic Nanofluids Containing PVP-Coated Ag Nanoparticles Using Mode-Mismatched Dual-Beam Thermal Lens Technique

Plasmonic nanofluids have found applications in many fields, for example, coolants, solar collectors, and theranostics agents. For such applications, an important parameter is the thermal diffusivity. In this communication, we present an experimental study concerning the dependence of the thermal diffusivity of highly diluted aqueous plasmonic nanofluids containing PVP-coated silver nanoparticles on the concentration. Measurements were made by employing the time resolved mode-mismatched thermal lens technique and the results show an enhancement of the thermal diffusivity, when compared to that of the carrier fluid, on increasing the number density of the nanoparticles and being rather constant as a function of the power of the pump beam.

Thermal diffusivity of ferrofluids as a function of particle size determined using the mode-mismatched dual-beam thermal lens technique

Ferrofluids are colloids of superparamagnetic nanoparticles that are envisaged for use in hyperthermia, which is based on nonradiative relaxation after interaction with a high-frequency magnetic field or light. For such applications, an important parameter is the thermal diffusivity. In this communication, we present an experimental study of the dependence of thermal diffusivity of ferrofluids on the size of the magnetite nanoparticles by employing the mode-mismatched thermal lens technique. The results show a huge enhancement of the thermal diffusivity by increasing the average size of the nanoparticles, while the number density of the nanoparticles is maintained as constant.

Thermal mirror and thermal lens techniques for semitransparent material characterization

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.

Thermal quenching of the fluorescence quantum efficiency in colquiriite crystals measured by thermal lens spectrometry

The dual-beam mode-mismatched thermal lens technique was used to study the temperature dependence of the absolute fluorescence quantum efficiency (η) of a thermal-quenching fluorescence (TQF) process in Cr3+-doped colquiriite crystals (LiSAF and LiSGaF), from 300 to 450 K. The research was developed at a low excitation-power level in order to eliminate the energy-transfer upconversion effect. The results showed that TQF is the main loss mechanism involved. The thermal diffusivity, the thermal conductivity, and the specific heat of the samples were also measured in the same temperature range.

Time-resolved Z-scan and thermal lens measurements in Er +3 and Nd +3 doped fluoroindate glasses

In rare earth ion doped solids, a resonant non-linear refractive index, n 2, appears when the laser pumps one of the ion excited states and the refractive index change is proportional to the excited state population. In these solids there are usually thermal and non-thermal lensing effects, where the non-thermal one is due to the polarizability difference, Δ α, between excited and ground states of the ions. We have used the time resolved Z-scan and a mode-mismatched thermal lens technique with an Ar + ion laser in Er +3 (20ZnF 2–20SrF 2–2NaF–16BaF 2–6GaF 3–(36− x)InF 3– xErF 3, with x=1, 2, 3 and 4 mol%) and Nd +3 (20SrF 2–16BaF 2–20ZnF 2–2GdF 3–2NaF–(40− x)InF 3– xNdF 3, with x=0.1, 0.25, 0.5–1 mol%) doped fluoroindate glasses. In both samples we found that the non-linear refraction is due to the thermal effect, while the non-thermal effect is negligible. This result indicates that in fluoride glasses Δ α is very small (less than 10 −26 cm 3). We also measured the imaginary part of the non-linear refractive index ( n 2″) due to absorption saturation.

Mode-mismatched thermal lens determination of temperature coefficient of optical path length in soda lime glass at different wavelengths

The time-resolved and steady-state mode-mismatched thermal lens technique has been used to determine the temperature coefficient of optical path length ds/dT at different wavelengths of soda lime glasses (72 wt % SiO2, 18 wt % Na2O, 10 wt % CaO, and 70.5 wt % SiO2, 17.5 wt % Na2O, 10 wt % CaO, 2 wt % Fe2O3). The aberrant model, which takes into account the thickness change of the sample and is more realistic than the parabolic treatment when used to describe the thermal lens effect, was used as the theoretical model. The results showed that ds/dT is (2.1±0.1)×10−6 K−1 at 632.8 nm and (2.4±0.1)×10−6 K−1 at 442 nm for the undoped sample and (4.66±0.03)×10−6 K−1 at 632.8 nm and (6.1±0.1)×10−6 K−1 at 442 nm for the iron-doped sample. The greater value of this parameter found for the doped sample at the absorption band (442 nm) was associated with the bigger value of the temperature coefficient of the electronic polarizability caused by the presence and environment of Fe3+ iron in the structure of the glass.

Time-resolved thermal lens measurement of thermal diffusivity of soda—lime glass

The time-resolved mode-mismatched thermal lens technique has been used to determine a precise value for the absolute thermal diffusivity of soda—lime glass (70.5 wt% SiO 2, 17.5 wt% Na 2O, 10 wt% CaO and 2 wt% Fe 2O 3). The thermal diffusivity was found to be (4.9±0.3) × 10 −3 cm 2/s which is in good agreement with the value obtained by photoacoustic spectrometry ((5.1±0.1) × 10 −3 cm 2/s). The technique is non-contacting and non-destructive.