Spectrosc. J., Volume 1, Issue 3 (December 2023) – 5 articles

Spectroscopic ellipsometry (SE), a non-invasive optical technique, is a powerful tool for characterizing surfaces, interfaces, and thin films. By analyzing the change in the polarization state of light upon reflection or transmission through a sample, ellipsometry provides essential parameters such as thin film thickness (t) and optical constants (n, k). This review article discusses the principles of ellipsometry, including the measurement of key values ∆ and Ψ, and the complex quantity ρ. The article also presents the Fresnel equations for s and p polarizations and the importance of oblique angles of incidence in ellipsometry. Data analysis in ellipsometry is explored, including the determination of bandgap and data referencing the electrical properties of materials. The article emphasizes the importance of choosing the appropriate models to fit ellipsometric data accurately, with examples of the Cauchy and Lorentz models. Additionally, the Kramers–Kronig relations are introduced, illustrating the connection between real and imaginary components of optical constants. The review underscores the significance of ellipsometry as a non-destructive and versatile technique for material characterization across a wide range of applications. Full article

This study aims to provide the dairy industry with a direct control model focused on milk coagulation by using multifiber probes to determine parameters in the curding process, such as cutting time, at a lower cost. The main objective of the research is to confirm that a multifiber NIR light scattering probe can be used to predict the elastic modulus of curd during milk coagulation in cheese production. Two randomized complete block designs were used with a 3 × 3 factorial arrangement of three protein levels (3%, 3.5% and 4%) and three wavelengths (870 nm, 880 nm and 890 nm). Using a multifiber probe at a wavelength of 880 nm allowed obtaining a better optical response of the sensor during enzymatic milk coagulation than the 870 nm. It showed greater sensitivity to variations in the protein content of the milk and lower variation in the response. The multifiber probe at a wavelength of 880 nm generated a NIR light backscatter profile like those obtained with other systems. The results showed that the prediction model parameters had a variation as a function of the protein content, which opens the possibility of improving the prediction model’s performance substantially. Furthermore, the initial voltage obtained with the probe responded linearly to the different protein levels in milk. This fact would make it possible, at least theoretically, to estimate protein concentration with the same inline probe for G’ determination, facilitating the incorporation of a corrective protein factor in the prediction models using a single instrument. Full article

Recent studies have indicated that terahertz time-domain spectroscopy (THz-TDS) can stably and efficiently acquire output spectra using an affordable and compact multimode laser diode (MMLD) with delayed optical feedback as the light source. This research focused on a numerical analysis of the optimal conditions for employing an MMLD with delayed optical feedback (a chaotic oscillating laser diode) in THz-TDS utilizing multimode rate equations. The findings revealed that the intermittent chaotic output generated by the MMLD, characterized by concurrent picosecond pulse oscillations lasting several tens of picoseconds, proved to be highly effective for THz-TDS. By appropriately setting the amounts for the injection current and optical feedback and the delay time for the optical feedback, intermittent chaotic oscillation could be attained within a considerably broad parameter range. The generation of intermittent chaotic oscillations was confirmed by observing their characteristic asymmetric spectral shapes. Moreover, both the MMLD output spectrum and the THz-TDS output spectrum exhibited consistently stable shapes at the microsecond scale, demonstrating the attractor properties inherent in an MMLD with delayed optical feedback. Full article

We studied the painted decorations found during recent restoration work in the Alexander Palace in Tsarskoye Selo. Optical/laser spectroscopic methods were applied to obtain a characterization of the materials, pigments, and binders in use and, possibly, their degradation. We analyzed samples of the original Art Nouveau style decoration that was detached in 2019 during conservation work at the State Office of Emperor Nicholas II. A combination of Raman microscopy, infrared spectroscopy, and elemental analysis (obtained from the optical emission following laser plasma formation) allowed us to obtain detailed information on the materials used. The precious pigments of the artist’s green-blue palette and the binder used (drying oil) were identified. A mixture of blue (Prussian blue and ultramarine blue), white (lead white and barium white), and yellow (chrome yellow and zinc yellow) pigments determined the different blue hues used. The use of bronze paint in the dark blue area, which was identified as a brass powder applied with a drying oil as a binder, was also demonstrated. Full article

Etherified cellulose derivatives, in contrast to cellulose, are soluble in water at room temperature and have a wide variety of applications. One of their most important characteristics is their decrease in solubility with temperature. The objective of this work was to study the rotational isomerism of the side chains of hydroxypropyl cellulose (HPC) in aqueous solution as sole solute and in the presence of chloride, sulfate, and barium ions as a function of temperature. Infrared Attenuated Total Reflectance spectroscopy was used to measure changes in the side-chain rotational isomerism using the structurally sensitive methylene wagging region as the probe. Decreases in end-gauche and kink conformers were observed. Principal component analysis revealed the presence of multiple forms of HPC at higher molecular weight. The precipitation of HPC as the temperature was increased was accompanied by a reduction in the numbers of end-gauche and kink conformers. Full article