2,649 research outputs found
Polarization properties and dispersion relations for spiral resonances of a dielectric rod
Dielectric microcavities based on cylindrical and deformed cylindrical shapes
have been employed as resonators for microlasers. Such systems support spiral
resonances with finite momentum along the cylinder axis. For such modes the
boundary conditions do not separate and simple TM and TE polarization states do
not exist. We formulate a theory for the dispersion relations and polarization
properties of such resonances for an infinite dielectric rod of arbitrary
cross-section and then solve for these quantities for the case of a circular
cross-section (cylinder). Useful analytic formulas are obtained using the
eikonal (Einstein-Brillouin-Keller) method which are shown to be excellent
approximations to the exact results from the wave equation. The major finding
is that the polarization of the radiation emitted into the far-field is linear
up to a polarization critical angle (PCA) at which it changes to elliptical.
The PCA always lies between the Brewster and total-internal-reflection angles
for the dielectric, as is shown by an analysis based on the Jones matrices of
the spiraling rays.Comment: submitted to JOSA
Calibrating evanescent-wave penetration depths for biological TIRF microscopy
Roughly half of a cells proteins are located at or near the plasma membrane.
In this restricted space the cell senses its environment, signals to its
neighbors and ex-changes cargo through exo- and endocytotic mechanisms. Ligands
bind to receptors, ions flow across channel pores, and transmitters and
metabolites are transported against con-centration gradients. Receptors, ion
channels, pumps and transporters are the molecular substrates of these
biological processes and they constitute important targets for drug discovery.
Total internal reflection fluorescence microscopy suppresses background from
cell deeper layers and provides contrast for selectively imaging dynamic
processes near the basal membrane of live-cells. The optical sectioning of
total internal reflection fluorescence is based on the excitation confinement
of the evanescent wave generated at the glass-cell interface. How deep the
excitation light actually penetrates the sample is difficult to know, making
the quantitative interpretation of total internal reflection fluorescence data
problematic. Nevertheless, many applications like super-resolution microscopy,
colocalization, fluorescence recovery after photobleaching, near-membrane
fluorescence recovery after photobleaching, uncaging or
photo-activation-switching, as well as single-particle tracking require the
quantitative interpretation of evanescent-wave excited images. Here, we review
existing techniques for characterizing evanescent fields and we provide a
roadmap for comparing total internal reflection fluorescence data across
images, experiments, and laboratories.Comment: 18 text pages, 7 figures and one supplemental figur
Dielectric lens antennas
Dielectric lens antennas are attracting a renewed interest for millimeter- and submillimeter-wave applications where they become compact, especially for configurations with integrated feeds usually referred as integrated lens antennas. Lenses are very flexible and simple to design and fabricate, being a reliable alternative at these frequencies to reflector antennas. Lens target output can range from a simple collimated beam (increasing the feed directivity) to more complex multi-objective specifications. This chapter presents a review of different types of dielectric lens antennas and lens design methods. Representative lens antenna design examples are described in detail, with emphasis on homogeneous integrated lenses. A review of the different lens analysis methods is performed, followed by the discussion of relevant lens antenna implementation issues like feeding options, dielectric material characteristics, fabrication methods, and a few dedicated measurement techniques. The chapter ends with a detailed presentation of some recent application examples involving dielectric lens antennas
Self-confined light waves in nematic liquid crystals
The study of light beams propagating in the nonlinear, dispersive, birefringent and nonlocal medium of nematic liquid crystals has attracted widespread interest in the last twenty years or so. We review hereby the underlying physics, theoretical modelling and numerical approximations for nonlinear beam propagation in planar cells filled with nematic liquid crystals, including bright and dark solitary waves, as well as optical vortices. The pertinent governing equations consist of a nonlinear Schrödinger-type equation for the light beam and an elliptic equation for the medium response. Since the nonlinear and coupled nature of this system presents difficulties in terms of finding exact solutions, we outline the various approaches used to resolve them, pinpointing the good agreement obtained with numerical solutions and experimental results. Measurement and material details complement the theoretical narration to underline the power of the modelling
Aperiodic nano-photonic design
The photon scattering properties of aperiodic nano-scale dielectric
structures can be tailored to closely match a desired response by using
adaptive algorithms for device design. We show that broken symmetry of
aperiodic designs provides access to device functions not available to
conventional periodic photonic crystal structures.Comment: 23 pages, LaTex, 8 postscript figure
Interactions of self-localized optical wavepackets in reorientational soft matter
The interaction of optical solitary waves in nematic liquid crystals, nematicons and vortices, with other nematicons and localised structures, such as refractive index changes, is reviewed. Such interactions are shown to enable simple routing schemes as a basis for all-optical guided wave signal manipulation
Reflection properties of a Gaussian laser beam from multilayer dielectric films
Thesis (Master)--Izmir Institute of Technology, Electronics and Communication Engineering, Izmir, 2010Includes bibliographical references (leaves: 83-85)Text in English; Abstract: Turkish and Englishxi, 85 leavesA laser microphone is a surveillance device that uses a laser beam to detect sound vibrations in a distant object. The object is typically inside a room where a conversation is taking place, and can be anything that can vibrate (for example, picture or window) in response to the sound waves of the conversation. The object preferably has a smooth surface. The laser beam is directed into the room through a window, reflected off the object and returned to a receiver that converts the beam to audio signal. The beam is mostly bounced off the window itself. Usually these kinds of devices are used by surveillance intelligence in some parts of governments and these kinds of weapons analyze the laser beam which reflects from window. In this thesis a countermeasure to the detection of laser beam is analyzed. In order to make this possible, the reflection from dielectric stratified surfaces of a Gaussian laser beam needs to be described. The reflected beam profile of electromagnetic radiation exposes to various effects different from reflected plane waves. Gaussian beams which reflect from a dielectric slab experience in a shifting maximum point in one direction; lateral shift, focal shift and angular divergence are the shift and distortion of the beam profile. The Gaussian beam propagates in z direction and broadens in transverse plane, in two dimensions and is decomposed into plane wave components. Upon analyzing the reflection coefficient and beam profile, reduction of beam power after reflection from stratified films is described
Bosonic enhancement of spontaneous emission near an interface
We show how the spontaneous emission rate of an excited two-level atom placed
in a trapped Bose-Einstein condensate of ground-state atoms is enhanced by
bosonic stimulation. This stimulation depends on the overlap of the excited
matter-wave packet with the macroscopically occupied condensate wave function,
and provides a probe of the spatial coherence of the Bose gas. The effect can
be used to amplify the distance-dependent decay rate of an excited atom near an
interface.Comment: 6 pages, 3 figure
Helmholtz algebraic solitons
We report, to the best of our knowledge, the first exact analytical algebraic solitons of a generalized cubic-quintic Helmholtz equation. This class of governing equation plays a key role in photonics modelling, allowing a full description of the propagation and interaction of broad scalar beams. New conservation laws are presented, and the recovery of paraxial results is discussed in detail. The stability properties of the new solitons are investigated by combining semi-analytical methods and computer simulations. In particular, new general stability regimes are reported for algebraic bright solitons
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