Rosette based metamaterial for circularly polarized terahertz waves manipulation

Metamaterials that respond resonantly in interaction with the terahertz (THz) electromagnetic waves are significant for the achievement of diverse optical functionalities in THz spectral range [1]. Also, they are virtually desirable platforms for investigating chiral effects which rise due to different interaction of metamaterials with left and right circularly polarized light [2,3]. Light polarization is an important feature of electromagnetic waves and manipulation of polarization plays pivotal role in various areas such as communications, imaging and sensing. One of potential applications of the THz metadevices is for protein quality control in the biotechnology or food industries [4]. Chiral properties of metamaterial can be modified via different external influences, such as by changing the interlayer twist angle, adding a dielectric spacer, or modulating its thickness. Twisting or rotating achiral layered structures in parallel planes enables engineering of the extrinsic chirality and consequential optical performance. For example, the twist angle from counterclockwise rotation of an upper layer with respect to the one under it, leads to a left-handed stacking geometry [5]. In this study, we performed numerical simulations of the metamaterial structure in terahertz frequency range, 0.25-0.75 THz. The numerical simulations were done for the case of two parallel gold rosettes on sapphire substrates in which we analyzed the influence of rotating one rosette with respect to the another on chiral properties. Two geometries of the rosette based structures were studied. First geometry is based on resonator which consists of two same parallel rosettes and the second one of two parallel rosettes, but one of them is trimmed.IX International School and Conference on Photonics : PHOTONICA2023 : book of abstracts; August 28 - September 1, 2023; Belgrad

Study of thiacyanine dye J-aggregates on single silver nanoparticle assemblies by surface enhanced Raman scattering and atomic force microscopy

Silver nanoparticles (AgNPs) capped with dye molecules and their J-aggregates often have remarkable optical properties that can lead to applications ranging from nanoscale sensing, light harvestering and bio-labelling to advanced composite materials for novel active and nonlinear optical devices. Here we investigate the J-aggregation of a thiacyanine dye (TC) on the surface of citrate capped AgNP nanoasseblies in which the average diameter of individual AgNPs is around 10 nm. Combining Raman mapping, surface-enhanced Raman spectroscopy (SERS) and atomic force microscopy (AFM), we study the influence of TC concentration on its J-aggregation on AgNPs surface. The TC – AgNPs assemblies were deposited onto freshly cleaved highly oriented pyrolytic graphite and mica surfaces. The spectral signature of citrate ions is identified by (i) the O-H band around 220 cm-1, (ii) the C-H band around 2960 cm-1 and (iii) pronounced blinking in the 1000-1800 cm-1 range. In contrast, dye molecules adsorbed on the nanoparticles are recognized by several stable Raman bands between 200 and 1600 cm-1. In situ AFM measurements indicate that the 'hot spots' are formed either on large single nanoparticles (diameter > 100 nm) or within aggregates of small nanoparticles (with diameters in the 10 - 50 nm range). However, only the latter are found to yield a citrate or TC dye SERS signal. Our study indicates that even in highly concentrated dye solutions, some citrate ions remain attached to the nanoparticles.2nd Optical Nanospectroscopy Conference : March 18-20, Dublin, Ireland, 2015.The second annual conference of COST Action MP130

Influence of chemical fixation process on primary mesenchymal stem cells evidenced by Raman spectroscopy

In investigation of (patho)physiological processes, cells represent frequently used analyte as an exceptional source of information. However, spectroscopic analysis of live cells is still very seldom in clinics, as well as in research studies. Among others, the reasons are long acquisition time during which autolysis process is activated, necessity of specified technical equipment, and inability to perform analysis in a moment of sample preparation. Hence, an optimal method of preserving cells in the existing state is of extreme importance, having in mind that selection of fixative is cell lineage dependent. In this study, two commonly used chemical fixatives, formaldehyde and methanol, are used for preserving primary mesenchymal stem cells extracted from periodontal ligament, which are valuable cell source for reconstructive dentistry. By means of Raman spectroscopy, cell samples were probed and the impact of these fixatives on their Raman response was analyzed and compared. Different chemical mechanisms are the core processes of formaldehyde and methanol fixation and certain Raman bands are shifted and/or of changed intensity when Raman spectra of cells fixed in that manner are compared. In order to get clearer picture, comprehensive statistical analysis was performed

Photoluminescence spectroscopy of CdSe nanoparticles embedded in transparent glass

In this paper we present photoluminescence measurements of CdSe nanoparticles embedded in transparent glass. Sample is prepared using an original technique, which combines both heat treatment and ultraviolet laser irradiation. Photoluminescence spectra displayed one main emission band at 2.14 eV. We identify this bands energy as basic interband transition in CdSe nanoparticle. We calculated energy of basic (1s(h)-1s(e)) transition in spherical CdSe quantum dot (QD), within infinite potential barrier, in effective-mass approximation. On the basis of this model, average radius of synthesized CdSe QDs is about 3 nm, which is in consistence with AFM measurements and UV-VIS absorption measurements