Twist-tunable moir\'e optical resonances

Multilayer stacks of twisted optical metasurfaces are considered as a prospective platform for chiral nanophotonic devices. Such structures are primarily used for the realization of circularly polarized light sources, artificial optical rotation, and circular dichroism. At the same time, the behavior of their hybrid photonic modes is strongly affected by the moir\'e-pattern of superimposed periodic constituents. In this work, we show that moir\'e-periodicity in bilayer dielectric photonic crystal slabs leads to an arise of unlimitedly narrow optical resonances, which are very sensitive to the relative twist and gap width between the sublayers. We demonstrate the structure providing twist-tuning of the hybrid mode wavelength in the range of 300--600~nm with quality factor varying from~$10^2$~up~to~$10^5$ correspondingly. The obtained results pave the wave for the utilization of moir\'e-assisted effects in multilayer photonic crystal slabs

Chiral light in twisted Fabry-P\'erot cavities

Fundamental studies of the interaction of chiral light with chiral matter are important for the development of techniques that allow handedness-selective optical detection of chiral organic molecules. One approach to achieve this goal is the creation of a Fabry-P\'erot cavity that supports eigenmodes with a desired electromagnetic handedness, which interacts differently with left and right molecular enantiomers. In this paper, we theoretically study chiral Fabry-P\'erot cavities with mirrors comprising one-dimensional photonic crystal slabs made of van der Waals As$_2$S$_3$, a material with one of the highest known in-plane anisotropy. By utilizing the anisotropy degree of freedom provided by As$_2$S$_3$, we design Fabry-P\'erot cavities with constitutional and configurational geometrical chiralities. We demonstrate that in cavities with constitutional chirality, electromagnetic modes of left or right handedness exist due to the chirality of both mirrors, often referred to as handedness preserving mirrors in the literature. At the same time, cavities with configurational chirality support modes of both handednesses due to chiral morphology of the entire structure, set by the twist angle between the optical axes of the upper and lower non-chiral anisotropic mirrors. The developed chiral Fabry-P\'erot cavities can be tuned to the technologically available distance between the mirrors by properly twisting them, making such systems a prospective platform for the coupling of chiral light with chiral matter.Comment: 33 pages, 9 figure

Chiral light in twisted Fabry-P\'erot cavities

Fundamental studies of the interaction of chiral light with chiral matter are important for the development of techniques that allow handedness-selective optical detection of chiral organic molecules. One approach to achieve this goal is the creation of a Fabry-P\'erot cavity that supports eigenmodes with a desired electromagnetic handedness, which interacts differently with left and right molecular enantiomers. In this paper, we theoretically study chiral Fabry-P\'erot cavities with mirrors comprising one-dimensional photonic crystal slabs made of van der Waals As$_2$S$_3$, a material with one of the highest known in-plane anisotropy. By utilizing the anisotropy degree of freedom provided by As$_2$S$_3$, we design Fabry-P\'erot cavities with constitutional and configurational geometrical chiralities. We demonstrate that in cavities with constitutional chirality, electromagnetic modes of left or right handedness exist due to the chirality of both mirrors, often referred to as handedness preserving mirrors in the literature. At the same time, cavities with configurational chirality support modes of both handednesses due to chiral morphology of the entire structure, set by the twist angle between the optical axes of the upper and lower non-chiral anisotropic mirrors. The developed chiral Fabry-P\'erot cavities can be tuned to the technologically available distance between the mirrors by properly twisting them, making such systems a prospective platform for the coupling of chiral light with chiral matter

Nearly perfect routing of chiral light by plasmonic grating on slab waveguide

Grating couplers are widely used to couple waveguide modes with the far field. Their usefulness is determined not only by energy efficiency but also by additional supported functionality. In this paper, we demonstrate a plasmonic grating on a silicon nitride slab waveguide that couples both TE and TM waveguide modes with circularly polarized light in the far field. Specifically, we experimentally confirmed that circularly polarized light excites TE and TM modes propagating in opposite directions, and the direction is controlled by the handedness. The routing efficiency for normally incident light reaches up to 95%. The same structure operates in the outcoupling regime as well, demonstrating up to 97% degree of circular polarization, where the handedness is determined by the polarization and propagation direction of outcoupled modes. Our results pave the way for the realization of polarization-division multiplexers and demultiplexers, integrated circular polarization emitters, as well as detectors of the polarization state of the incident optical field

Multicentric survey of patient doses in fluoroscopy guided diagnostic and interventional cardiac procedures: comparison with Diagnostic Reference Levels and follow-up levels for patients at risk for radiation induced skin effects

Въведение. Интервенционалните кардиологични процедури, често са свързани с голямо облъчване на пациентите, поради което изискват специално внимание по отношение на защитата от появата на радиационно индуцирани ефекти при пациента.Материали и методи. Проучването на типичните стойности на дозата е проведено ретроспективно, в девет лечебни заведения, с общо четиринадесет ангиографски уредби. За две от най-често извършваните процедури - перкутанна коронарна интервенция (PCI) и коронарна артериография (CA) са изчислени типичните стойности на величините произведение керма-площ (КАП), кумулативна доза (КД) и време на скопия (ВС) и са сравнени с актуалните Национални диагностични референтни нива (НДРН) за България. Извършен е анализ на данните по отношение на риска от възникване на кожно индуцирани ефекти, вследствие на интервенционалните кардиологични процедури.Цел. 1) да се представят и анализират типичните стойности на величината КАП за най-често провежданите кардиологични процедури - перкутанна коронарна интервенция и коронарна артериография в кардиологични отделения с голяма работна натовареност и да се сравнят с НДРН; 2) да се сравнят дозите на пациентите с публикуваните в Наредба 2 нива за проследяване, за установяване на пациенти с риск за възникване на радиационно индуцирани ефекти.Резултати. Резултатите показват, че типични стойности на изследваните величини за PCI и CA при някои от уредбите, са по-високи от НДРН. Във всяко от разглежданите лечебни заведения има пациенти с поне едно превишено ниво за проследяване за процедура PCI.Изводи. Резултатите показват потенциал за оптимизиране, както на работата в отделенията с високи типични стойности на дозата, така и при уредбите с много ниски типични стойности на изследваните величини. При проследените пациенти не се наблюдават оплаквания и поява на радиационно индуциран ефект. Изготвянето и въвеждането в рутинната клинична практика на процедури за рутинно прилагане на „Инструкцията за пациента след проведена интервенционална/и процедура/и с по-голяма степен на сложност и дълго време на скопия“ ще позволи навременна диагностика и навременно лечение на кожните ефекти в следствие на проведените кардиологични процедури под рентгенов контрол. Introduction. Interventional cardiac procedures are often associated with high patient exposure and therefore require special care in protecting patients from radiation-induced effects.Materials and methods. A retrospective study of typical patients’doses was performed in nine hospitals, with a total number of fourteen angiography systems. The typical values for kerma-area product (KAP), cumulative dose (CD) and fluoroscopy time (FT) for two of the most commonly performed procedures - percutaneous coronary intervention (PCI) and coronary arteriography (CA), were calculated and compared with the Bulgarian National Diagnostic Reference Levels (NDRL). Data analysis, regarding the risk of radiation-induced skin effects due to interventional cardiac procedures, was performed.Aim. 1) to present and analyze the typical KAP values for PCI and CA procedures in cardiology departments with high workload and to compare them with the NDRL; 2) to compare the patient doses with the follow-up levels published in Ordinance 2, to identify patients at risk for radiation-induced effects.Results. The results show that typical values for PCI and CA procedures for some of the angiography systems are higher than the NDRL. In all investigated departments there are patients with at least one exceeded follow-up level for PCI.Conclusions. The results show a potential for optimization in the departments with both high or very low typical dose or FT values. No radiation-induced effect was observed in the followed-up group of patients. The introduction of procedure with "Instruction to the patient after an interventional cardiac procedure(s) with greater complexity and a long fluoroscopy time" for patient follow-up and its regular implementation into the routine clinical practice will help for timely diagnosis and treatment of radiation-induced skin effects after cardiac procedures under fluoroscopy control