Search results for "FLE"
showing 10 items of 3517 documents
Nearly zero ultraflattened dispersion in photonic crystal fibers.
2000
We present a procedure for achieving photonic crystal fibers with nearly zero ultraflattened group-velocity dispersion. Systematic knowledge of the special guiding properties of these fibers permits the achievement of qualitatively novel dispersion curves. Unlike the behavior of conventional fibers, this new type of dispersion behavior permits remarkably improved suppression of third-order dispersion, particularly in the low-dispersion domain.
Determination of the spatial extension of the surface-plasmon evanescent field of a silver film with a photon scanning tunneling microscope.
1993
A photon scanning tunneling microscope is employed to probe the surface-plasmon field in the evanes- cent region of a silver film for p (parallel to the plane of incidence) and s (perpendicular to the plane of incidence) polarizations of the light beam at several angles of incidence near the critical angle. The in- teraction between the field and the probe is measured and compared to theoretical calculations involving a single four-media model. A systematic analysis of images obtained for several positions of the optical fiber above the film is presented and it is shown that, for tip-to-sample distances smaller than half the wavelength of the incoming light, the collected intensity curves a…
Direct Bragg grating writing in a hybrid PDMS/silica photonic crystal fiber
2011
Infiltration of materials into the air holes of the PCFs can potentially manipulate their optical properties creating a new category of fibers termed as hybrid PCFs [1] and many devices based on hybrid PCFs have been developed [2–5]. Recently, a hybrid PCF with poly-dimethylsiloxane (PDMS) elastomer inclusions has been demonstrated [6]. PDMS is widely used in the area of photonics and optofluidics. It is highly transparent with a refractive index ∼1.41, conserving the total internal reflection guiding mechanism of the hybrid PCF. When PDMS is irradiated with UV light its refractive index increases [7]. In this paper we present the first example of a Bragg grating directly written using UV l…
Donor and acceptor guided modes in photonic crystal fibers.
2000
We present a triangular photonic-crystal-fiber structure that exhibits guided modes simultaneously above and below the first conduction band. We achieve this configuration by decreasing the size of one of the airholes (the defect) in a specific triangular lattice. More generally, we analyze the behavior of guided modes that depends on the size of the defect. Defects generated by decreasing or increasing the size of one of the holes produce donor or acceptor guided modes, respectively, in analogy with impurity levels in solid-state crystals. We conclude that the guiding mechanism for both donor and acceptor modes is produced by a unique phenomenon of multiple interference by a periodic struc…
Theoretical and experimental analysis of photonic structures for fluorescent concentrators with increased efficiencies
2008
In this study we present a theoretical and experimental analy- sis of the application of photonic band stop filters on top of photovoltaic fluorescent concentrators in order to increase the photon collection efficiency. The light guiding effect of the fluorescent concentrator relies on total internal reflection. The escape cone of total internal reflection is their major loss mechanism. Our ray tracing simulation allows to calculate the beneficial effect of photonic band stop reflection filters, which reduce these losses, and to simulate the angular distribu- tion of the light trapped in the concentrator. We present simula- tions of the optical properties of 1D and 3D photonic structures an…
Experimental measurements for studying angular and spectral variation of thermal infrared emissivity
2004
One condition for precise multiangle algorithms for estimating sea and land surface temperature with the data from the Advanced Along Track Scanning Radiometer is accurate knowledge of the angular variation of surface emissivity in the thermal IR spectrum region. Today there are very few measurements of this variation. The present study is conducted to provide angular emissivity measurements for five representative samples (water, clay, sand, loam, gravel). The measurements are made in one thermal IR broadband (8-13 microm) and three narrower bands (8.2-9.2, 10.3-11.3, and 11.5-12.5 microm) at angles of 0 degrees-60 degrees (at 5 degrees increments) to the surface normal. The results show a…
Resolution of the photon scanning tunneling microscope: influence of physical parameters
1992
Abstract The photon scanning tunneling microscope (PSTM) is the photon analogue of the electron scanning tunneling microscope (ESTM). It uses the evanescent field due to total internal reflection (TIR) of a light beam in a prism modulated by a sample placed on the base of the prism. Our experimental results shown details which present a lateral size as small as 200 A. The PSTM axial resolution is more difficult to evaluate. It is a function of the roughness of the sample. For very smooth samples, images shown an axial resolution of about 10 A. At last we discuss how both lateral and axial resolution can be affected by several parameters such as the tip surface distance and the roughness of …
Prediction of organic carbon and total nitrogen contents in organic wastes and their composts by Infrared spectroscopy and partial least square regre…
2017
Middle and near infrared (MIR and NIR) were employed to determine organic carbon (OC) and total nitrogen (TN) in different soil organic amendments including wastes, composts and mixtures of composts and organic wastes. Prediction models based on partial least squares (PLS) regression from the spectra of untreated samples were built. Different spectra preprocessing strategies were adopted and the best number of latent variable was evaluated using leave-one-out cross-validation. Attenuated total reflectance (PLS-ATR-MIR) and diffuse reflectance (PLS-DR-NIR) models were built and evaluated from root mean square error of cross validation and prediction (RMSECV and RMSEP), coefficients of determ…
The wettability of ash from burned vegetation and its relationship to Mediterranean plant species type, burn severity and total organic carbon content
2011
Abstract Immediately following a wildfire, a layer of ash and charred material typically covers the ground. This layer will gradually be reduced, being redistributed by rainfall, wind or animals, by partial dissolution and by incorporation into the soil. Ash can increase or decrease the post-fire runoff and erosion response, depending upon the soil and ash properties and the ash thickness. One aspect of ash that has remained unknown and which may affect the variability in the hydrological response of the burned soil is its wettability. This study examines the wettability of ash using the Water Drop Penetration Time (WDPT) test, its relationship with total organic carbon (TOC) content and co…
Recyclable and Light-Adaptive Vitrimer-Based Nacre-Mimetic Nanocomposites.
2021
Nacre's natural design consists of a perfect hierarchical assembly that resembles a brick-and-mortar structure with synergistic stiffness and toughness. The field of bioinspired materials often provides attractive architecture and engineering pathways which allow to explore outstanding property areas. However, the study of nacre-mimetic materials should not be limited to the design of its architecture but ought to include the understanding, operation, and improvement of internal interactions between their components. Here, we introduce a vitrimer prepolymer system that, once integrated into the nacre-mimetic nanocomposites, cures and cross-links with the presence of Lewis acid catalyst and …