1,335 research outputs found
Proceedings of the third French-Ukrainian workshop on the instrumentation developments for HEP
The reports collected in these proceedings have been presented in the third
French-Ukrainian workshop on the instrumentation developments for high-energy
physics held at LAL, Orsay on October 15-16. The workshop was conducted in the
scope of the IDEATE International Associated Laboratory (LIA). Joint
developments between French and Ukrainian laboratories and universities as well
as new proposals have been discussed. The main topics of the papers presented
in the Proceedings are developments for accelerator and beam monitoring,
detector developments, joint developments for large-scale high-energy and
astroparticle physics projects, medical applications.Comment: 3rd French-Ukrainian workshop on the instrumentation developments for
High Energy Physics, October 15-16, 2015, LAL, Orsay, France, 94 page
Accurate modelling of the optics of high resolution liquid crystal devices including diffractive effects
An accurate method to model the optical behaviour of liquid crystal (LC) devices, particularly suited to devices where diffractive effects are present is described here. An accurate electromagnetic modelling programme that takes into account the full non-uniformity and anisotropy of the LC has been developed. This is combined with an existing in-house LC finite element modelling programme based on the Landau – De Gennes theory, that uses the order tensor representation of the LC orientation and allows an accurate descriptions of structures containing LC defects and small features. The electromagnetic model is based on the total field/scattered field (TF-SF) approach to electromagnetic scattering problems and is implemented using finite differences in the frequency domain (FDFD) in a form that can accommodate perfectly matched layers (PMLs) and periodic boundary conditions. The resultant matrix problem is solved efficiently using an especially adapted form of a sweeping preconditioner and the generalised minimum residual method (GMRes). This method has been implemented in 2D and is demonstrated here with the design and analysis of a reconfigurable blazed phase grating that utilises an LC defect to produce an abrupt fly-back, with the capability of short periods and high diffraction efficiency
Design and fabrication of ultrathin nanophotonic devices based on metasurfaces
Wydział FizykiOd kilkuset lat badania natury światła fascynuje naukowców na całym świecie. W XVII wieku, holenderski astronom i matematyk, Willebrord Snellius zdefiniował pojęcie refrakcji światła, które później od jego nazwiska zostało nazwane prawem Snella. Prawo to wciąż jest szeroko stosowane, a jego uogólnienie w roku 2011 zaproponował prof. Capasso z Uniwersytetu Harvarda. Uogólnione prawo Snella pozwala na rozwijanie technik kontroli frontów falowych wykorzystując powierzchnie zmieniające ich fazę w transmisji lub w odbiciu, zwane metapowierzchniami. Uogólnione prawo Snella jest zgodne z zasadą Fermata a wytwarza się je przy użyciu bardzo małych struktur mogących arbitralnie modyfikować amplitudę, fazę, polaryzację fali światła. Mechanizm odpowiedzialny za to zjawisko można dostosować do konkretnych zakresów długości fali i jest szczególnie dobrze sprawdzone dla światła z zakresu widzialnego. W pracy doktorskiej przedstawiłem koncepcję wykorzystania metapowierzchni do projektowania kilku urządzeń nanofotonicznych. Zaprojektowałem w pełni dielektryczne filtry koloru na bazie krzemu, które efektywnie działają dla fal przechodzących i odbitych. Rozszerzyłem te badania również o projekt dynamicznych i przestrajalnych filtrów kolorów kontrolując polaryzację światła przy wykorzystaniu ciekłych kryształów. Następnie zaproponowałem koncepcję urządzenia wykorzystujące zjawisko impedancji powierzchniowej do sterowania transmisją i umożliwiając prowadzenie fal w płaszczyźnie falowodu kryształu fotonicznego.Light is one of the most fascinating research areas of science since the past few centuries and this century no exception. In 17th, Snell's law was introduced by Willebrord Snellius a Dutch astronomer and mathematician, which explain the properties of refraction and reflection of light. In 2011, prof. Capasso group from Harvard University generalized the
Snell's law and introduce a new way to modify the wave-front of the wave using phase varying surfaces. The modified Snell's law follows the Fermat principle for the phase changing surfaces. This phase changing surface can be created using tiny nanostructures to arbitrarily modified the amplitude, phase, polarization of the wave, commonly known
as metasurfaces. The concept is scalable to arbitrary wavelength range and very well followed especially in the visible range. In this thesis, I used the concept of metasurfaces
to design and fabricate the different nanophotonics devices. I design and fabricate the Si-based all-dielectric color filters which can be used in transmission and reflection mode. The color filter design presented in this thesis is very efficient due to the all dielectric material approach. I also extended the research to design dynamically tunable color filters with the aid of source polarisation and liquid crystal. Furthermore, I also proposed the surface impedance approach to control the in-plane transmission within the photonic crystal waveguide
Nonradiating Photonics with Resonant Dielectric Nanostructures
Nonradiating sources of energy have traditionally been studied in quantum
mechanics and astrophysics, while receiving a very little attention in the
photonics community. This situation has changed recently due to a number of
pioneering theoretical studies and remarkable experimental demonstrations of
the exotic states of light in dielectric resonant photonic structures and
metasurfaces, with the possibility to localize efficiently the electromagnetic
fields of high intensities within small volumes of matter. These recent
advances underpin novel concepts in nanophotonics, and provide a promising
pathway to overcome the problem of losses usually associated with metals and
plasmonic materials for the efficient control of the light-matter interaction
at the nanoscale. This review paper provides the general background and several
snapshots of the recent results in this young yet prominent research field,
focusing on two types of nonradiating states of light that both have been
recently at the center of many studies in all-dielectric resonant meta-optics
and metasurfaces: optical {\em anapoles} and photonic {\em bound states in the
continuum}. We discuss a brief history of these states in optics, their
underlying physics and manifestations, and also emphasize their differences and
similarities. We also review some applications of such novel photonic states in
both linear and nonlinear optics for the nanoscale field enhancement, a design
of novel dielectric structures with high- resonances, nonlinear wave mixing
and enhanced harmonic generation, as well as advanced concepts for lasing and
optical neural networks.Comment: 22 pages, 9 figures, review articl
Optical Nanostructures For Controllable And Tunable Optical Properties
Optical nanostructures are heterogeneous media containing subwavelength inclusions in periodic or aperiodic fashion. The optical properties of optical nanostructure can be controlled and tuned using their constituent material properties and spatial arrangement of the inclusions. While optical nanostructures have been widely studied, controllable and tunable nanostructures using low loss transparent materials has not been studied in detail in the literature. The objective of this research is to perform efficient design and analyses of controllable and tunable optical nanostructures using low loss transparent materials.
To that end, versatile and highly accurate numerical methods like finite different tie domain and plane wave expansion methods are reviewed first. These methods and compared in terms of their speed, accuracy, and memory requirement. Different kind of optical nanostructures, consisting of low index transparent materials, are analyzed to study their controllability. For example, single scatterers are optimized to obtain highly direction forward scattering using low index materials. Then, the minimum refractive index required for establishing optical bandgap in a planar periodic nanostructure was established. Using the bandgap, highly sensitive transparent sensors are designed using low index materials. It is found that the numerical methods can analyze small or periodic nanostructure, while requiring significant computational resources.
As an alternative to numerical modelling, analytical effective medium approximations are considered. The available approximations are reviewed, and their limitations are pointed out. Using the Mie scattering theory, the Maxwell-Garnett approximation is extended so that it can account for arbitrary size, as well as different physical structures, of the inclusions. The derived effective medium approximation is tested on a wide variety of optical nanostructure, both periodic and aperiodic. Good agreement between analytical and experimental results are established. The utility of the approximation in designing controllable and tunable optical nanostructure is demonstrated by modelling the dynamic optical properties of magnetic colloids and verifying them experimentally. The effective medium approximation can be a very fast, and efficient method of modelling the controllable and tunable properties of optical nanostructure, when applied judiciously. The applicability, limits of validity, and limitation of the approximation is also discussed.
Using the analytical framework, controllable optical nanostructure that can mimic optical elements, e.g., focusing lenses, are designed. The relationship between physical structure of the inclusions and the imparted phase by the nanostructure is studied using effective medium approximation and numerical methods. The effective medium approximation can predict the imparted phase with high accuracy, while requiring a fraction of the computation resources compared to numerical methods. Based on the relationship between imparted phase and physical structure of the inclusions, it is possible to design optical nanostructure with controllable spatial phase profile. Using this property, nanostructured optical elements are designed. Their far-field properties are calculated using analytical scalar theory. The analytical results matched well with numerical and experimental results.
In conclusion, an analytical method for designing and analyzing tunable and controllable optical nanostructure is derived and verified with experimental results. The analytical method is significantly more efficient compared to numerical methods, while being similarly accurate compared to experimental results. The research in this work can lead to efficient design of optical nanostructure for many different fields
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