J.A. Sampaio

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.

Spectroscopic properties of water free Nd2O3-doped low silica calcium aluminosilicate glasses

Abstract In this work, low silica calcium aluminosilicate glasses (LSCA) doped with different concentrations of Nd 2 O 3 were prepared under vacuum conditions and investigated through spectroscopic measurements. UV, visible and near IR optical absorption spectra, IR luminescence spectra, and fluorescent time decay were measured. Judd–Ofelt model was used in conjunction with these data to calculate intensity parameters (Ω 2 ,Ω 4 and Ω 6 ), emission cross-section, radiative lifetime, branching ratio and fluorescence quantum efficiency. The up-conversion properties of Nd 3+ were investigated following ( 4 G 5/2 + 2 G 7/2 ) excitation, and both visible and UV up-conversion have been observed. These results combined with its high fluorescence quantum efficiency and excellent mechanical properties, suggest that this glass may be a candidate to be used as laser host material for near IR with a further possibility of application in the UV and visible spectral regions.

Rare-earth doped low silica calcium aluminosilicate glasses for near and mid infrared applications

The combination of properties such as chemical durability, transformation temperature, thermo-mechanical properties, refractory properties, phonon energy of about 800 cm−1 and infrared transparency up to 6 μm, recommend low silica (<7 wt%) calcium aluminosilicate glasses as hosts for laser applications. We have been investigating the physical properties of these glasses prepared by melting under vacuum conditions. This preparation procedure ensured minimum in OH content in the low silica calcium aluminosilicate glass hosts with fluorescence quantum efficiency of about 0.92 and 2.8 μm photoluminiscence, in samples co-doped with Er and Yb. In this paper, we review the thermal, mechanical and optical properties of these minimum OH content rare-earth-doped oxide glasses and discuss their potentials for near- and mid-infrared applications. Particular emphasis is given to the discussion of the new and promising optical properties of Er–Yb doped samples for biomedical applications.

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.

Structure and properties of water free Nd2O3 doped low silica calcium aluminate glasses

Abstract In this work, Nd 2 O 3 doped low silica calcium aluminate glasses have been melted under vacuum conditions. Measurements of thermal diffusivity, density, optical absorption coefficient, glass transformation temperature ( T g ), crystallisation temperature ( T x ), dilatometric softening temperature ( T d ) and Vickers microhardness have been carried out. The results provided information about the samples structure and showed that for Nd 2 O 3 concentration up to 5 wt% there was no devitrification of the samples. The decrease in hardness and thermal diffusivity was about 8%, while the density increased about 8% with the increasing concentration of Nd 2 O 3 . The thermomechanical properties combined with their quantum efficiency indicate that this material is a candidate for an active medium for solid-state lasers.

Rare earth doping effect on the elastic moduli of low silica calcium aluminosilicate glasses

Abstract Elastic moduli (E, G, K, ν) of calcium aluminosilicate glasses with m 1/2 and the thermal shock resistance is 339±102 W/m.

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.

Thermo-mechanical and optical properties of calcium aluminosilicate glasses doped with Er3+ and Yb3+

In this work a series of Er 2 O 3 and Yb 2 O 3 doped and Er 2 O 3 -Yb 2 O 3 co-doped low silica calcium aluminosilicate glasses have been melted at 1470°C under vacuum conditions. Measurements of optical absorption coefficient, mass density, refractive index, Vickers micro-hardness, glass transformation temperature (T g ) and crystallization temperature (T x ) have been carried out. The results showed that these glasses dissolved ∼1.5 mol% Er 2 O 3 and ∼1.1 mol% Yb 2 O 3 in their structure without devitrification and also that only small changes (∼10%) have been measured in their thermal. mechanical and optical properties.

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.