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An imaging Mueller matrix ellipsometer is used to measure structures in measuring fields in the micrometre range, which are too small for conventional ellipsometry. Line and grid structures are measured and evaluated with the help of numerical simulations using the finite element method to characterize the structure parameters.

To understand the dynamics of ultrashort-pulse laser ablation, the interpretation of ultrafast time-resolved optical experiments is of utmost importance. To this end, spatiotemporally resolved pump-probe ellipsometry may be utilized to examine the transiently changing dielectric function of a material, particularly when compared to two-temperature model simulations. In this work, we introduce a consistent description of electronic transport as well dielectric function for bulk aluminum, which enables unambiguous quantitative predictions of transient temperature and density variations close to the surface after laser excitation. Potential contributions of these temperature and density fluctuations to the proposed optical model are investigated. We infer that after the thermal equilibrium of electrons and lattice within a few picoseconds, the real part of the dielectric function mostly follows a density decrease, accompanied by an early mechanical motion due to stress confinement. In contrast, the imaginary part is susceptible to a complicated interaction between time-varying collision frequency, plasma frequency, and a density dependency of the interband transitions. The models proposed in this study permit an outstanding quantitative prediction of the ultrashort-pulse laser ablation’s final state and transient observables. Consequently, it is anticipated that in the future, these models will provide a quantitative understanding of the dynamics and behavior of laser ablation. Graphical abstract

We report on a dynamic metalorganic aerosol deposition (dyna-MAD) technique, that allows dynamic growth control of thin film heterostructures with complex oxide constituents. This method enables the deposition of gradient (or ‘graded’) heterostructures of (LaMnO3)x/(SrMnO3)y. In situ optical ellipsometry reveals a modified electronic and optical material’s response with changing amount of gradient. Structure and microstructure are characterized by means of x-ray diffraction and atomic force microscopy measurements, which confirm epitaxial thin film growth.

Titanium nitride film was deposited on a glass substrate by reactive magnetron sputtering. The composition and structure of the film were studied by SEM, XRD and XPS. The results show that the atomic ratio of titanium to nitrogen in the film is TiN1.05, and the crystal orientation of the film is mainly TiN (111). The optical properties of titanium nitride films in the wavelength range from 380nm to 2500nm were studied in detail using a spectral ellipsometer. Four commonly used dispersion models including Gaussian and Lorentz are compared to resolve the fitting effect of the ellipsometry spectrum of titanium nitride films. The fitting results were validated by reflection and transmission spectra. The results show that the Lorentz model combined with the Drude model is the best fit for the elliptic spectrum of titanium nitride films over the entire range of bands tested.

Superficial amorphization and re-crystallization of silicon in and orientation after irradiation by femtosecond laser pulses (790 nm, 30 fs) are studied using optical imaging and transmission electron microscopy. Spectroscopic imaging ellipsometry (SIE) allows fast data acquisition at multiple wavelengths and provides experimental data for calculating nanometric amorphous layer thickness profiles with micrometric lateral resolution based on a thin-film layer model. For a radially Gaussian laser beam and at moderate peak fluences above the melting and below the ablation thresholds, laterally parabolic amorphous layer profiles with maximum thicknesses of several tens of nanometers were quantitatively attained. The accuracy of the calculations is verified experimentally by high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (STEM-EDX). Along with topographic information obtained by atomic force microscopy (AFM), a comprehensive picture of the superficial re-solidification of silicon after local melting by femtosecond laser pulses is drawn.

Circularly polarized light is central to many photonic technologies, including circularly polarized ellipsometry-based tomography 1 , 2 , optical communication of spin information 3 and quantum-based optical computing and information processing 4 , 5 . To develop these technologies to their full potential requires the realization of miniature, integrated devices that are capable of detecting the chirality or ‘handedness’ of circularly polarized light. Organic field-effect transistors, in which the active semiconducting layer is an organic material, allow the simple fabrication of ultrathin, compact devices 6 , 7 , 8 . Here we demonstrate a circularly polarized light-detecting organic field-effect transistor based on an asymmetrically pure, helically shaped chiral semiconducting molecule known as a helicene 9 . Importantly, we find a highly specific photoresponse to circularly polarized light, which is directly related to the handedness of the helicene molecule. We believe that this opens up the possibility for the detection of the chirality of circularly polarized light in a highly integrated photonic platform. An organic field effect transistor featuring the chiral molecule helicene acts as a photodetector that is able to distinguish between left- and right-handed circularly polarized light.

We present a study on femtosecond laser treatment of amorphous hydrogen-containing carbon coatings (a-C:H). The coatings were deposited on silicon wafers by a plasma-assisted chemical vapour deposition (PA-CVD), resulting in two different types of material with distinct properties (referred to as “absorbing” and “semi-transparent” coatings in the following). The samples were laser-treated with single fs-laser pulses (800 nm center wavelength, 35 fs pulse duration) in the ablative regime. Through a multi-method approach using topometry, Raman spectroscopy, and spectroscopic imaging ellipsometry, we can identify zones and thresholds of different fluence dependent effects and have access to the local dielectric function. The two coating materials react significantly different upon laser treatment. We determined the (non-ablative) modification threshold fluence for the absorbing coating as$$3.6\\times {10}^{-2}$$3.6 × 10 - 2  Jcm −2 and its ablation threshold as 0.22 Jcm −2 . The semi-transparent coating does not show such a low-fluence modification but exhibits a characteristic interference-based intra-film ablation mechanism with two distinguishable ablation thresholds at 0.25 and 0.28 Jcm −2 , respectively. The combination of tailored layer materials and correlative imaging spectroscopic methods delivers new insights into the behaviour of materials when treated with ultrashort-pulse laser radiation. Graphical abstract

Towards new and improved techniques in liquid biopsy for the diagnosis of diseases, this study reports experimental evidence of a rapid and reliable method based on terahertz (THz) time-domain spectroscopic ellipsometry (TDSE) for the early diagnosis of kidney-related diseases, using the detection of uric acid (UA) content in urine. Employing a custom-built THz-TDSE system, we analyzed the absorption and dispersion response of synthetic urine samples with varying concentrations of UA. The technique provides a prompt indication of UA presence and concentration, thanks to the sensitivity of THz waves to intermolecular interactions such as hydrogen bonding. The results clearly show a linear correlation between the UA concentration and changes in the absorption spectra of urine in the frequency window 0.2–1.2 THz, with the minimum detectable UA concentration being approximately close to the upper limit of normal UA levels in urine. The increase in the absorption coefficient as a function of the UA concentration provides a means for a quantifiable measure of the UA biomarker in urine for assessing disease stage. This study proves that THz-TDSE is capable of detecting UA at concentrations relevant for early-stage diagnosis of renal diseases, with an estimated sensitivity of 0.2 g/L in the region where the material response is linear.

Surface plasmon resonance (SPR) is an optical sensing technique that is capable of performing real-time, label-free and high-sensitivity monitoring of molecular interactions. SPR biosensors can be divided according to their operating principles into angle-, wavelength-, intensity- and phase-interrogated devices. With their complex optical configurations, phase-interrogated SPR sensors generally provide higher sensitivity and throughput, and have thus recently emerged as prominent biosensing devices. To date, several methods have been developed for SPR phase interrogation, including heterodyne detection, polarimetry, shear interferometry, spatial phase modulation interferometry and temporal phase modulation interferometry. This paper summarizes the fundamentals of phase-sensitive SPR sensing, reviews the available methods for phase interrogation of these sensors, and discusses the future prospects for and trends in the development of this technology.

The paper considers the reflection of a circularly polarized light wave from a periodic nanostructure. The method of characteristic matrices was used to calculate the ellipsometric parameters ρ 0 and Δ of reflected light. It is shown that a wave initially polarized in the left circle changes polarization upon reflection, turning into an elliptically polarized wave. The results obtained for an ideal periodic medium are compared with the results of reflection from a periodic medium with a single defect - the upper layer of the original periodic medium is replaced by an absorbing dielectric layer. The analysis showed that the spectral dependences of the ellipsometric parameters for two structures, periodic and defective, differ significantly. In the range of wavelengths λ from 0.4 μm to 0.6 μm, the ellipsometric parameter ρ 0 for the considered periodic medium and the medium with a defect differ significantly from each other - where the maximum is for one medium, there is approximately the minimum for the other. In turn, the parameter Δ demonstrates a significant difference for the two structures in the wavelength range λ from 0.46 μm to 0.55 μm. The use of circularly polarized light demonstrates wide possibilities for studying defects in periodic nanostructures.