Measurement of phase transitions and thermal diffusivity in agar using a thermal wave resonator cavity

In the present work, the photopyroelectric (PPE) technique is proposed using a Thermal Wave Resonator Cavity (TWRC) to measure the temperature dependence of the thermal diffusivity of agar. Also, to determine the liquid to gel phase transition temperature on several agar concentration samples. The thermal diffusivity of agar as a function of temperature was measure by means of a cavity length variation due to thermal expansion of the TWRC, instead of the typical mechanic length variation through a micrometer. A change in the liquid to gel transition phase temperature was detected as a function of agar concentration, getting lower values as the agar concentration decrease

Preparation and characterization by thermal lens spectroscopy of SiO2_2 monoliths having optical memory properties due to the incorporation of Mn and Cr

Using the sol-gel technique, monoliths of sol-gel based silica (SiO$_2$) containing low concentrations of Mn and Cr were prepared. These monoliths were obtained without cracks by applying gradual thermal treatments in the alcogel state. These materials have an optical memory effect. We induced and observed this optical memory effect through the configuration of a thermal lens system. This effect was permanently stored in the materials studied, showing a high contrast in the transmission between the unaffected zone and the zone where a permanent gradient refractive index was induced

Synthesis by wet chemistry and characterization of LiNbO3 nanoparticles

Actually, lithium niobate (LiNbO3) has been used for optical wavelength conversion and ultrafast optical signal processing because of its outstanding rapid nonlinear optical response behavior, low switching power and broad conversion bandwidth. LiNbO3nanoparticles, which belong to the ferroelectric oxide class, were synthesized by chemical reaction with wetchemistry. Their sizedistributionwascenteredaround200 nm. Xray diffraction (XRD) and scanning electron microscopy (SEM) were used to further investigate the quality of the obtained LiNbO3powders.The present work shows thatby employingthis chemical method the correct stoichiometric phasewas obtained. This wascorroborated by XPS (X-Ray Photoelectron Spectroscopy) results. Also, the nanoparticles showed a defined crystallinity and uniform morphology. This way of obtaining nanoparticles is innovative because of its low cost and simple way to reproduce it. It isan important method of increasing the surfacearea, controlling thephase purityand reducing theparticle size distribution. The samples were obtained under low temperature annealing at500, 650 and 800 ºC. Those features can be controlled using variables such temperature, time of synthesis,and calcination. In previous worksit wasfound that hydrothermal methods offer many advantages over conventional ceramic synthesis methods

Synthesis by wet chemistry and characterization of LiNbO3 nanoparticles

Actually, lithium niobate (LiNbO3) has been used for optical wavelength conversion and ultrafast optical signal processing because of its outstanding rapid nonlinear optical response behavior, low switching power and broad conversion bandwidth. LiNbO3nanoparticles, which belong to the ferroelectric oxide class, were synthesized by chemical reaction with wetchemistry. Their sizedistributionwascenteredaround200 nm. Xray diffraction (XRD) and scanning electron microscopy (SEM) were used to further investigate the quality of the obtained LiNbO3powders.The present work shows thatby employingthis chemical method the correct stoichiometric phasewas obtained. This wascorroborated by XPS (X-Ray Photoelectron Spectroscopy) results. Also, the nanoparticles showed a defined crystallinity and uniform morphology. This way of obtaining nanoparticles is innovative because of its low cost and simple way to reproduce it. It isan important method of increasing the surfacearea, controlling thephase purityand reducing theparticle size distribution. The samples were obtained under low temperature annealing at500, 650 and 800 ºC. Those features can be controlled using variables such temperature, time of synthesis,and calcination. In previous worksit wasfound that hydrothermal methods offer many advantages over conventional ceramic synthesis methods