Quality control and non-destructive monitoring are of notable interest of food and pharmaceutical industries. It relies on the ability of non-invasive inspection which can be employed for manufacturing process control. We hereby apply terahertz (THz) time-domain spectroscopy as non-destructive technique to monitor pure and degraded oils as well as hydrocarbon chemicals. Significant differences in the spectra of refractive index (RI) and absorption coefficient arising from the presence of ester linkages in the edible and technical oils were obtained. Explicit increase from 1.38 to 1.5 of the RI in all THz spectrum range was observed in hydrocarbons and mono-functional esters with the increase of molar mass. This fact is in contrast of RI dependence on molar mass in multi-functional esters, such as Adipate or vegetable oils, where it is around 1.54. Degradation products, Oleic Acid (OA) and water in particular, lead only to some changes in absorption coefficient and RI spectra of vegetable oils. We demonstrate that complex colloidal and supramolecular processes, such as dynamics of inverse micelles and oil hydrolysis, take part during oil degradation and are responsible for non-uniform dependence of optical properties on extent of degradation.

Fibonacci or bifocal terahertz (THz) imaging is demonstrated experimentally employing a silicon diffractive zone plate in continuous wave mode. Images simultaneously recorded in two different planes are exhibited at 0.6 THz frequency with the spatial resolution of wavelength. Multifocus imaging operation of the Fibonacci lens is compared with a performance of the conventional silicon phase zone plate. Spatial profiles and focal depth features are discussed varying the frequency from 0.3 to 0.6 THz. Good agreement between experimental results and simulation data is revealed.

Temperature dependent photoluminescence (PL) of MgZnO epitaxial layers with high Mg content were studied to understand the effect of carrier localization on the PL dynamics, including the PL dependence on excitation power density and temperature. A double blueshift of the PL peak position with increase of measurement temperature was discovered. The blueshift took place at low as well as high temperature and could be attributed to the effect of carrier localization. It has been deduced that the randomly distributed carrier localization centers in the MgZnO films create two energy separated Gaussian-shape density-of-states tails in the vicinity of the fundamental band gap edge. Filling of these tail states by the thermally activated carriers with increase of temperature causes the temperature-induced double blueshift of the PL peak position. By analyzing the temperature dependent PL spectra, two parameters, σ and γ were extracted, which characterize the average energy depth distribution of the localizing potential field fluctuations. The value of these parameters were found to depend on the Mg content and crystalline structure of the MgZnO epitaxial layers.

Optical characterization of molecular-beam-epitaxy-grown ZnO and MgZnO epitaxial layers on sapphire (0001) substrates is presented. The parameters such as carrier recombination time and optical gain coefficient are analyzed. Radiative recombination mechanisms of ZnO in dense quasiparticle system are discussed. The ZnO epilayers even with lower structural quality are tolerable for applications in optoelectronics as light emitters.