Use of thermal lens spectroscopy to measure the thermal diffusivity, during the gelation process, of sol–gel materials added with Mn

Abstract

In this article, we have studied the evolution of the thermal diffusivity of SiO2-based sol–gel material containing various amounts of Mn. The thermal diffusivity was obtained using thermal lens spectroscopy. The thermal diffusivity measured as a function of time, from the precursor liquid solution to the solid glass, shows a behavior with three distinct regimes. These regimes correspond to the different stages of glass formation, the hydrolysis, gelation, and solidification stages. The materials show an optical memory effect, which is produced by the irradiation with a focused laser beam. The laser beam produces a gradient in the refractive index, which can be permanently stored in the material. This local change in the optical properties of the material can be read with a probe laser due to the strong diffraction pattern observed in the transmitted light.

Synthesis, characterization and local changes induced by a cw argon laser in silica glass xerogel doped with transition metal ions

“…Following these transient changes at the probe beam center we obtained the thermal diffusivity of the sample. Further experimental details about the thermal lens effect are described elsewhere [6][7][8][9][10][11][12][13][14][15][16][17][18][19]. The exposure of sol-gel monoliths to laser light with power intensities above 1 mW at incidence times longer than 0.5 min (energy density greater than 590 J/cm 2 ) produces permanent changes in the refraction index in the illuminated area.…”

Mechanical and thermal properties of SiO2–PMMA monoliths

“…The effect of this temperature distribution on the probe laser beam is an optical path length change, which can be expressed as an additional phase shift on the probe beam wave front after passing through the sample. The central intensity of the probe beam in the far field as a function of time is given by the next equation [14,16,18,20,22,[24][25][26] …”

“…We used thermal lens spectroscopy in the unmatched mode to measure the thermal diffusivity (a) of the monoliths. Further experimental details about the thermal lens technique are described elsewhere [14][15][16][17][18][19][20][21][22][23][24][25][26]. The theoretical treatment of the TL effect considers the temperature distribution in the sample produced by the excitation laser beam.…”