Grazing incidence systems with multiple reflections

The asymmetric response of a gyrotropic medium to left and right circularly polarized light, as manifested in specular reflection, provides (1) a sensitive test of the electrodynamics of chiral media and (2) a novel spectroscopic method particularly suitable for nontransparent chiral materials in microquanitites. The differential reflection of circularly polarized light, d = (IL-IR)/(IL+IR) (where IL and IR is the reflected-light flux of specialized polarizations), is ordinarily linearly proportional to the chiral parameter(s) and is of the order 105-10-6 for many materials. However, for total reflection near critical angle, d is a nonlinear function of the chiral parameter(s) and can exceed the above range by several orders of magnitude.1 This enhancement can be further increased by multiple reflection. For N passes at the critical angle from a weakly absorbing chiral sample, d is approximately N times greater than for a single pass. The enhancement factor is smaller than N to the extent that the incident angle departs from critical angle or N exceeds an optimal value. For sufficiently high N, the angular range of enhancement becomes too narrow to be of practical utility.

A novel microring resonator sensor coated with a single negative metamaterial (SNM) layer is proposed. The dispersion relation of hollow cylindrical dielectric waveguide covered with a SNM layer is derived, and resonant frequencies of the corresponding whispering gallery mode are computed. We find that there is a good agreement between the theoretical results and numerical results of resonant frequencies and electric field distributions. Compared with traditional resonator sensor, the sensitivity and resolution are significantly enhanced by SNM, and the Q factor can be tailored by adjusting the distance between the waveguide and the microring.

Low temperature sensitivity and low spectral contrast are serious but common issues for most Fabry Perot (FP) sensors with an air cavity. In this paper, a high-temperature-sensitive and spectrum-contrast-enhanced Fabry Perot interferometer (FPI) is proposed and experimentally demonstrated. The device is composed of a hollow cylindrical waveguide (HCW) filled with polydimethylsiloxane (PDMS) and a semi-elliptic PDMS end face. The semi-elliptic PDMS end face increases the spectral contrast significantly due to the focusing effect. Experimentally, the spectral contrast is 11.97 dB, which is two times higher than the sensor without semi-elliptic PDMS end face. Ultra-high temperature sensitivity of 3.1501 nm/°C was demonstrated. The proposed sensor exhibits excellent structural stability, high spectral contrast and high temperature sensitivity, showing great potential in biomedicine, industrial manufacturing, agricultural production and other applications.

There has been very little work done in the past to extend the wavelength range of fiber image bundles to the IR range. This is due, in part, to the lack of IR transmissive fibers with optical and mechanical properties analogous to the oxide glass fibers currently employed in the visible fiber bundles. Our research is aimed at developing high-resolution hollow-core coherent IR fiber bundles for transendoscopic infrared imaging. We employ the hollow glass waveguide (HGW) technology that was used successfully to make single-HGWs with Ag/AgI thin film coatings to form coherent bundles for IR imaging. We examine the possibility of developing endoscopic systems to capture thermal images using hollow waveguide fiber bundles adjusted to the 8-10?mum spectral range and investigate the applicability of such systems. We carried out a series of measurements in order to characterize the optical properties of the fiber bundles. These included the attenuation, resolution, and temperature response. We developed theoretical models and simulation tools that calculate the light propagation through HGW bundles, and which can be used to calculate the optical properties of the fiber bundles. Finally, the HGW fiber bundles were used to transmit thermal images of various heated objects; the results were compared with simulation results. The experimental results are encouraging, show an improvement in the resolution and thermal response of the HGW fiber bundles, and are consistent with the theoretical results. Nonetheless, additional improvements in the attenuation of the bundles are required in order to be able to use this technology for medical applications.

The study of the optical properties of the GaAs with point defects

Multiple internal reflection spectroscopy: a sensitive non-destructive probe for interfaces and nanometric layers

Theoretical investigations of the elastic, electronic, optical and thermodynamics properties of SrSi

An optical biosensor based on attenuation of the light intensity during multiple reflections in a planar waveguide has been developed for water pollution monitoring. The planar waveguide consists of a 190 nanometer thick silicon nitride (Si₃N₄) core layer sandwiched between 1.5 micrometer thick silicon dioxide (SiO₂) cladding layers. Composite polyelectrolyte self-assembled membranes containing Cyclotetrachromotropylene (CTCT) as an indicator and enzymes, such as Urease or Acetylcholine Esterase (AChE) were deposited on top of silicon nitride core layer within a 4 × 6 mm sensing window. Experimental studies on the light propagation through the planar waveguide show the advantages of this method over conventional UV-visible absorption spectroscopy. It was found that the planar waveguide sensitivity is higher by several orders of magnitude than that for UV-visible absorption spectroscopy. The respective enzyme reactions as well as their inhibition by heavy metal ions were studied by monitoring the light intensity in the planar waveguide. Cadmium (Cd²⁺) and lead (Pb²⁺) ions were registered in very low concentrations down to 1 ppb with the planar waveguide transducer. The enzymes used were inhibited differently by the above pollutants, which is promising for the development of enzyme sensor arrays.

Neutron diffraction by perfect crystals excited into mechanical resonance vibrations

We present the core thickness dependence of the propagation loss and the polarization dependence loss (PDL) of hollow waveguides of various air core thicknesses. The addition of phase-control layers to GaAs/AlAs multilayer mirrors enables us to reduce the PDL by one order of magnitude. The propagation loss and the PDL of a 5 µm air core hollow waveguide are 2.8 dB/cm and 1.7 dB/cm, respectively, which are currently limited by the reflectivity (0.998) of the GaAs/AlAs multilayer mirrors.

Imaging simulation of a dark field imperfection evaluation arrangement for spherical optical surface based on reverse ray tracing

An analytical sea surface optical properties model in the infrared band is described. It allows the introduction of multiresolution in the simulated field-of-view answering the need in computed images including any observational configurations. It is valid for fully-developed seas, includes shadowing and hiding functions but not breaking and foam nor multiple reflections. For the model validation purposes, the MIRAMER field campaign took place in the Mediterranean sea during May 2008, both ground-based and on board an oceanographic ship. Radiometric datasets along with the associated environmental measurements have been collected in various environmental and observation conditions. First campaign results are presented in this paper.

The structural (under 5 GPa), electronic, optical and thermodynamic (under 30 GPa) properties of bulk-PtSe2 and two-dimensional 1-Layer-PtSe2 were investigated via the first-principle calculations. The calculated equilibrium parameters are in agreement with the available experimental data, investigated using X-ray diffraction, and the theoretical results. Electronic structure calculations show that the bulk-PtSe2 is a semimetal, while the 1-Layer-PtSe2 is a semiconductor with an indirect band gap width of 0.18 eV. We also calculated their optical properties and thermodynamic properties under high temperature and high pressure.

Novel bithienyl-benzimidazoles were synthesised in good to excellent yields, by a one-step reaction via Na2S2O4 reduction of o-nitroaniline in the presence of formyl-bithiophenes. Using this simple and versatile method, benzimidazoles were directly obtained from several o-nitroanilines and aldehydes, via a reductive cyclization without purification of any intermediate. Evaluation of the optical and solvatochromic properties of these compounds was carried out.

The neglect of multiple reflections between clouds and the earth's surface leads to an underestimate of the downward flux of solar radiation reaching the earth's surface. This underestimate is most pronounced in regions of persistent cloud cover and high surface albedos—the snow- and ice-covered regions of the high latitude zone, for example. Since the rate of snow melt (and thus snow albedo) depends upon the downward flux, neglect of multiple reflection is most serious in climatic models that predict snow and ice cover. Two simple algebraic expressions to account for multiple reflections in climate models are given and are shown to be limiting cases of a more general formula. Since this more general formula depends on the spatial distribution of subgrid-scale cloud cover amounts, an unambiguous definition of cloud amount over a GCM-scale grid square cannot be given, even if perfect knowledge of the optical properties of the subgrid-scale clouds were in hand. However, the uncertainties in downward solar flux at the earth's surface (or the albedo of the combined cloudiness-surface system) introduced by lack of knowledge of the two-dimensional geometric distribution of fractional cloud cover are shown to be generally less than 10%, most likely less than the errors in predicting cloud cover amounts or from the neglect of three-dimensional effects of finite-sized clouds.