The study of the reduction of an optical fiber by chemical etching has been suggested to determine the concentrations of sucrose in water and their refractive indices by evanescent waves using a coherent infrared source. The cladding of a single-mode optical fiber was removed at a rate of ~3.27 µm min −1 using hydrofluoric acid until it reached a diameter of 7.3 µm, similar to the core of the fiber. This fiber was used to characterize sucrose solutions at different amounts employing a continuous wave infrared laser source at 1550 nm. The sucrose was dissolved in water to evaluate the quantitative sensor response based on the transmission relationship. The experimental results showed that the refractive indices obtained by the evanescent absorbance were in the range of 1.31-1.44 for concentrations of sucrose between 0% (water) to 65%. Additionally, it was determined that for concentrations higher than 65% of sucrose, the refractive index of the solution is similar to the core of the fiber, and therefore the total internal reflection was not possible. The results obtained in this work suggest that the etched optical fiber can be used as a refractive index sensor, which may play an important role in chemical applications.

Cadmium sulfide thin films were prepared by chemical bath on glass substrates at 80°C. CdS was Er-doped during the growth process by adding water-diluted Er(NO3)33∙H2O to the CdS aqueous growing solution. The relative volume of the doping solution was varied in order to obtain different doping levels. The crystalline structure of CdS:Er films was cubic zinc blende for all the doped layers prepared. The (111) interplanar distance has an irregular variation with the Er doping level. Consequently, the band gap energy (Eg) firstly increases and afterward diminishes becoming, at last, approximately constant at around Eg=2.37eV. For higher doping levels, in the as-grown films, dark electrical conductivity (σ) values reach 1.8×10−2Ω−1cm−1 at room temperature. The logarithm of σ vs 1∕kT plot, where k is Boltzmann’s constant and T the absolute temperature, indicates an effective doping of CdS as a result of the Er introduction into the lattice of the material. Hall effect measurements reveal a n-type doping with 2.8×1019cm−3 as maximum carrier density.

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This paper reports an improvement to the chopper z-scan technique for elliptic Gaussian beams. This improvement results in a higher sensitivity by measuring the ratio of eclipsing time to rotating period (duty cycle) of a chopper that eclipses the beam along the main axis. It is shown that the z-scan curve of the major axis is compressed along the z-axis. This compression factor is equal to the ratio between the minor and major axes. It was found that the normalized peak-valley difference with respect to the linear value does not depend on the axis along which eclipsing occurs.

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