Konstantinos Moutzouris

Temperature-dependent visible to near-infrared optical properties of 8 mol% Mg-doped lithium tantalate

We report the experimental determination of the ordinary and extraordinary refractive index of 8 mol% Mg-doped congruent lithium tantalate (MCLT). Refractive index measurements cover a spectral range from 450nm to 1550nm and temperatures varying from 22°C to 200°C. Experimental data are fitted to a temperature-dependent dispersion relation that has not been previously used with this material family. Based on this relation, various optical properties of MCLT are calculated, including thermo-optic coefficient, group velocity dispersion, phase matching curve and temporal walk-off. In an additional quasi-phase-matching second-harmonic-generation experiment it is shown that the proposed dispersion relation may be used to predict grating period with remarkable nanometer-scale accuracy.

Visible to near-infrared refractive properties of freshly-excised human-liver tissues: marking hepatic malignancies

The refractive index is an optical constant that plays a significant role in the description of light-matter interactions. When it comes to biological media, refraction is understudied despite recent advances in the field of bio-optics. In the present article, we report on the measurement of the refractive properties of freshly excised healthy and cancerous human liver samples, by use of a prism-coupling technique covering the visible and near-infrared spectral range. Novel data on the wavelength-dependent complex refractive index of human liver tissues are presented. The magnitude of the real and imaginary part of the refractive index is correlated with hepatic pathology. Notably, the real index contrast is pointed out as a marker of discrimination between normal liver tissue and hepatic metastases. In view of the current progress in optical biosensor technologies, our findings may be exploited for the development of novel surgical and endoscopic tools.

A neural network approach for the prediction of the refractive index based on experimental data

This article presents a systematic approach for correlating the refractive index of different material kinds and forms with experimentally measured inputs like wavelength, temperature, and concentration. The correlation is accomplished using neural network models, which can deal effectively with the nonlinear nature of the problem without requiring a predefined form of equation, while taking into account all the parameters affecting the refractive index. The proposed methodology employs the powerful radial basis function network architecture and the neural network training procedure is accomplished using an innovative algorithm, which provides results with increased prediction accuracy. The methodology is applied to two cases, involving the estimation of the refractive index of semiconductor material crystals and an ethanol–water mixture and the results show that the refractive index predictions are accurate approximately to the same number of decimal places as the real measurements. Comparisons with other neural network training methods, but also with empirical forms like the Sellmeier equation, highlight the superiority of the proposed approach.

Fiber Optic Measurement System for Fresnel Reflection Sensing: Calibration, Uncertainty, and Exemplary Application in Temperature-Modulated Isothermal Polymer Curing

Fiber Bragg grating (FBG) sensors and Fresnel reflectometer sensors have emerged as promising tools for monitoring process state parameters during composite manufacturing. However, multifunctional fiber optic sensor systems exploiting the versatile nature of these sensors are not commercially available. In principle, most FBG measurement systems are equipped with the required hardware to measure the refractive index (RI) by interrogating Fresnel reflectometer sensors. However, the implications of using an FBG system for this purpose have not been previously studied. Therefore, we calibrated a commercial FBG measurement system in the refractive index range between 1.3 and 1.6 at 1550 nm, based on data comparison with an independent RI measurement technique, and determined the measurement uncertainty. Additionally, we investigate the suitability of the proposed Fresnel reflectometer sensor for use in temperature-modulated isothermal epoxy curing experiments for detecting the glass transition by exploiting a concept that resembles temperature modulated optical refractometry. This paper describes in detail the calibration routine, the determination of the measurement uncertainty, and the application of Fresnel reflectometer sensors for glass transition detection during isothermal curing. We observed an offset between the measured RI and the theoretical value in the range of

Calibration and uncertainty of a fibre optic measurement system for Fresnel reflectometer sensors

10^{{{\hbox{--}} 3}}

Electrical characterization of polymer matrix — TiO2 filler composites through isothermal polarization / depolarization currents and I–V tests

. The measurement system uncertainty was found to be of the order of

Refractive, dispersive and thermo-optic properties of twelve organic solvents in the visible and near-infrared

10^{{{\hbox{--}} 4}}

Complex refractive index of normal and malignant human colorectal tissue in the visible and near-infrared.

. That is comparable to the accuracy of most commercial refractometers. Furthermore, we showed that Fresnel reflectometer sensors are suitable for glass transition detection during isothermal curing. The results show that commercial FBG measurement systems are viable options for multifunctionality sensing in online process monitoring applications.

WSN Open Source Development Platform: Application to Green Learning

A four-channel fibre optic measurement system for fibre Bragg grating (FBG) sensors was used to measure the refractive index of fluids with Fresnel reflectometer sensors prepared from SMF28e singlemode fibres. The fibre optic measurement system was calibrated with five high-purity organic fluid samples in the refractive index range between 1.3 and 1.6. The light source had a wavelength of 1550 nm and the fluid samples were held at 24 °C. In total, 400 refractive index measurements were performed. The calibration of the fibre optic measurement system was performed with a linear correction function. The combined uncertainty of the refractive index measurements with the fibre optic measurement system was found to be in the order of 10−4.

Developing Open Source Dataloggers for Inquiry Learning

Specimens of polymer matrix — ceramic TiO2 filler composites were prepared. The contribution of the filler content on the electrical conductivity and energy storage properties of the samples was examined. I–V and Isothermal Polarization/Depolarization Current (IPC/IDC) measurements were conducted. Dc conductivity values directly calculated from the I–V curves exhibited excellent agreement with corresponding values derived from the IPC/IDC recordings. Standard models were employed for fitting the IPC/IDC data. In specific, the short and the very long depolarization times were fitted by use of power laws of different slopes, while the intermediate depolarization times were fitted as a sum of three exponential decays. The present study reveals a strong dependence of the depolarization and polarization processes, as well as of the dc conductivity, on the filler concentration.