S.M. Lima

Mode-mismatched thermal lens spectrometry for thermo-optical properties measurement in optical glasses: a review

Abstract In this work, the application of thermal lens spectrometry (TLS) to study thermo-optical and spectroscopic properties of optical glasses is described. The theoretical basis for quantitative measurements is discussed together with the advantages and limitations of the method as compared with conventional measurements. The technique is applied to determine the thermal diffusivities, temperature coefficient of optical path length changes, d s/ d T , and the fluorescence quantum efficiencies of several glasses such as fluorides, chalcogenides, chalcohalides, soda lime and low silica calcium aluminosilicate. For some of these glasses, the effect of glass composition on thermo-optical properties was studied. For aluminosilicate glasses was observed an 8% decrease of the thermal diffusivity with the increase of Nd2O3 doping. Five kinds of fluoride glasses were studied and it was observed that fluorindate and fluoaluminate present better thermo-optical properties compared to fluorozirconate glasses: thermal diffusivity ∼ 20% higher and d s/ d T ∼ 50% lower (in modulus). All fluoride glasses had negative d s/ d T and all the other glasses a positive d s/ d T . For fluoride glasses, the TLS measurements were performed up to the glass transition temperature ( T g ). Near T g thermal diffusivity decreases and d s/ d T increases, both by one order of magnitude. The TLS was used to determine fluorescence quantum efficiency and concentration quenching in Nd3+-doped glasses (aluminosilicate and fluorozirconate). These results were compared with the Judd–Ofelt calculations.

Multiwavelength thermal lens determination of fluorescence quantum efficiency of solids: Application to Nd3+-doped fluoride glass

A multiwavelength thermal lens (TL) method was developed to determine the fluorescence quantum efficiency of solids. The experiments have been performed in Nd3+-doped fluoride glasses, using five different excitation wavelengths: 514, 576, 741, 796, and 867 nm. In this work, the absolute value of fluorescence quantum efficiency can be obtained by the linear dependence of the TL signal with the excitation wavelength. Our results suggest that the method can be applied to study a wide range of fluorescent materials, with a special ability to be used for measurements of highly transparent materials with very low TL effect.

Spectroscopy thermal and optical properties of Nd3+ -doped chalcogenide glasses

We investigated the spectroscopic, thermo-optical and mechanical properties of 70% Ga2S3:30% La2S3 (mol%) chalcogenide glass and this composition doped with 0.05, and 0.2 mol% Nd2S3, prepared by melt-quenching the sulphides in a vitreous carbon crucible in a silica ampoule. The fluorescence quantum efficiency for the 0.05 mol% Nd3+ doped sample, obtained by thermal lens technique was 1.01±0.07 and the lifetime of the fluorescence of this sample was 78.00±0.05 s. The thermal diffusivity of these samples (2.7±0.1)×10-3 cm2 s-1 was determined by the thermal lens method.

High fluorescence quantum efficiency of 1.8 μm emission in Tm-doped low silica calcium aluminate glass determined by thermal lens spectrometry

In this work, thermal lens spectrometry is performed to determine the fluorescence quantum efficiency (η) of the 3F4 level (1.8 μm emission) of 4 and 5 wt % Tm-doped water free low silica calcium aluminate glass. The η value obtained for both high Tm contents was approximately 30%, which is in agreement with the Judd–Ofelt calculation. It is also verified that heat generation under 0.79 μm pumping, which presents a high quantum defect, is minimized by a cross-relaxation mechanism. The high η values, and the excellent chemical and thermomechanical properties indicate this system is a potential host material for diode-pumped laser sources operating in the midinfrared spectral range.

Nonlinear refraction spectroscopy in resonance with laser lines in solids

We report a simple extension of the Z-scan technique that permits a spectral line-shape measurement of the real and the imaginary parts of n2. In this technique the sample is placed at the peak position of the usual Z-scan curve while the laser frequency is scanned. We employed this method to investigate the nonlinear susceptibility of the R lines of ruby and alexandrite, using a cw dye laser. This susceptibility can be explained by the resonant interaction and by a nonresonant contribution that is due to the difference in polarizability between Cr3+ excited and ground states. For ruby, the nonresonant contribution to the technique is 1 order of magnitude larger than the resonant contribution. However, for alexandrite both contributions are comparable, and their interference leads to a shift between n2′ and n2″ spectra that is not observed in ruby.

Temperature dependence of fluorescence quantum efficiency of optical glasses determined by thermal lens spectrometry

Abstract In this work thermal lens spectrometry is applied to determine the fluorescence quantum efficiency, η, of Nd2O3-doped low silica calcium aluminosilicate glasses as a function of the temperature. The experiments were performed in the temperature range between 22 and 180 ° C. The results showed that the decrease in η observed with increase in the temperature of the samples was larger for the larger Nd2O3-doping concentrations. This observation indicates that the non-radiative relaxation processes induced by Nd–Nd ion interactions may be the dominant mechanism responsible for the η reduction. The results indicate that the thermal lensing technique is a useful tool to evaluate the effect of the active medium temperature in the performance of laser systems.

Thermal lens versus DTA measurements for glass transition analysis of fluoride glasses

In this work thermal lens spectrometry is applied to study fluoride glasses as a function of temperature. The experiments, in the temperature range between 20 and 300 °C, were performed to determine how the thermal lens technique can be compared with conventional differential thermal analyses (DTA) method. The results showed that the temperature dependence of the thermal lens signal amplitude provided a better definition in locating the glass transition as compared to the DTA data. We propose that the technique can be applied for the investigation of the phase transitions of glasses.

Fluorescence quantum efficiency measurements using the thermal lens technique

The single wavelength thermal lens (TL) method jointly with the multiwavelength TL method are used to determine the fluorescence quantum efficiency η of Nd3+-doped glasses and crystals. The concentration quenching and the upconversion parameter for Nd3+-doped solids is also described in this article. In addition, the TL method is used to study the temperature behavior of η for Cr3+-doped fluoride crystal.

Fluorescence quantum efficiency measurements of excitation and nonradiative deexcitation processes of rare earth 4f-states in chalcogenide glasses

Thermal lens spectroscopic measurements were performed to quantitatively determine the fluorescence quantum efficiency (eta) of different luminescence mechanisms in Nd3+ chalcogenide glasses. Low energy (<1.7 eV) direct resonant pumping at Nd3+ infrared lines resulted in eta ~1. High energy (~2.4 eV) indirect excitation via energy transfer (ET) from glass conduction band to Nd3+ 4f states, resulted in eta = ~0.4 (ET probability ~40%). A minimum eta ~0.2 was obtained for intermediate excitation energies (~2.2 eV) and attributed to back ET from the Nd3+ 4f state to the glass host.

Thermal lens and interferometric method for glass transition and thermo physical properties measurements in Nd 2 O 3 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.