Search results for "Refractive index"
showing 10 items of 332 documents
Characterizing weld pool surfaces from polarization state of thermal emissions
2013
International audience; In this Letter, a vision-based remote sensing methodology is proposed to measure the topography of weld pool surfaces from one single view. Thermal radiations emitted by the hot liquid metal at a wavelength within the arc plasma blind spectral window are acquired by a wavefront division polarimetric system. The refractive index of the liquid metal and the topography of the weld pool surface are inferred from the polarimetric state of the thermal radiations.
Ultrathin high-index metasurfaces for shaping focused beams
2015
The volume size of a converging wave, which plays a relevant role in image resolution, is governed by the wavelength of the radiation and the numerical aperture (NA) of the wavefront. We designed an ultrathin (λ/8 width) curved metasurface that is able to transform a focused field into a high-NA optical architecture, thus boosting the transverse and (mainly) on-axis resolution. The elements of the metasurface are metal-insulator subwavelength gratings exhibiting extreme anisotropy with ultrahigh index of refraction for TM polarization. Our results can be applied to nanolithography and optical microscopy. Spanish Ministry of Economy and Competitiveness (MEC) (TEC2013-50416-EXP).
Simple method for measuring bilayer system optical parameters
2012
A simple method for measuring bilayer system refractive indexes and thicknesses in the low absorbing part of spectra is demonstrated. The method is based on application of Savitzky - Golay smoothing filters and interference fringe separation in the reflected or transmitted spectra of the bilayer system. The refractive indexes and thicknesses are extracted from the wavelengths corresponding to extreme points in the spectrum. Due to the fact that wavelength difference of extreme points in the analyzed spectrum is defined by the product of both, the layer thickness and refractive index, one must generate an appropriate initial guess of these parameters. For refractive index approximation two d…
Mode family analysis for PMMA WGM micro resonators using spot intensity changes
2021
The whispering gallery modes (WGM) micro resonators are based on elliptical objects, which can be made from optically transparent materials, The geometry of the object enables optical wave circulating inside the ellipse using total internal reflection. If there is a monochromatic light source with constant intensity to the ellipse, constructive interference may be observed. Poly methyl methacrylate acrylic (PMMA) WGM micro resonators are commercially available with typical optical quality factor of 103-104. These could limit problems with WGM micro resonator expensive manufacturing. Thanks to advances in high resolution image processing, read-outs using spectroscopy (single photo detector) …
Increasing Nanoparticles’ Refractive Index Sensitivity
2012
Since the plasmon resonance of nanoparticles depends on the refractive index of the immediate environment, these particles form the basis of many sensing schemes . The sensitivity of plasmon sensors for the detection of changes in the environment varies greatly and depends on the particle material and its morphology (size and shape). To further increase this sensitivity by chemical modifications was another goal of my work.
Numerical study of photolithography system: electromagnetic differential method
2004
The R-matrix propagation algorithm is incorporated into the differential method to achieve an extended capability for modelling a photolithography systems. We show throughout this work the ability of the R-matrix algorithm and differential method to analyse gratings of arbitrary depth, profile, and conductivity without encountering numerical instabilities. We calculate the field intensity and the transmitted amplitudes in the 0 and −1 orders below different masks. We study also the influence of the various parameters (incidence, groove spacing, groove depth and index of refraction) on the field intensity maps and the transmittivity power. These results agree with the experimental patent: we…
Kerr self-cleaning of pulsed beam in an ytterbium doped multimode fiber
2017
International audience; We experimentally demonstrate that Kerr spatial self-cleaning of a pulsed beam can be obtained in an amplifying multimode optical fiber. An input peak power of 500 W only was sufficient to produce a quasi-single-mode emission from the double-clad ytterbium doped multimode fiber (YMMF) with non-parabolic refractive index profile. We compare the self-cleaning behavior observed in the same fiber with loss and with gain. Laser gain introduces new opportunities to achieve spatial self-cleaning of light in multimode fibers at a relatively low power threshold.
High third and second order non linearities of chalcogenide glasses and fibers for compact infrared non linear devices.
2008
Due to their intrinsic nature, chalcogenide glasses present attractive nonlinearities from third and second order, with values reaching between 10 and 1000 times those of silica. We present a study of their properties and their shaping with the purpose to reach efficient devices in the near-mid infrared.
Self-focusing in Terbium Gallium Garnet using Z-scan
1998
International audience; When illuminated near its resonance with an Ar ion laser beam (lambda=488 nm), laser induced thermal self-focusing is observed in Terbium Gallium Garnet. The crystal exhibits a strong intensity dependent refractive index change Dn. The Z-scan technique is used to study the beam waist change due to Dn. The refractive index is found to be well described by a quadratic spatial distribution model. Both the sign and the distribution coefficient of Dn are determined.
Quasi-phase-matched third harmonic generation in optical fibers using refractive-index gratings
2011
International audience; The purpose of this work is to demonstrate the quasi-phase-matching of third harmonic generation process in optical fibers using refractive-index gratings. We compare conversion efficiency calculated with analytical coupled modes theory and numerical approach employing system of coupled generalized nonlinear Schrödinger equation. Moreover, we show that introducing the phase matching condition that takes into account the nonlinear contribution to propagation constants significantly increases the conversion efficiency by several orders of magnitude. Finally we optimize the grating constant to maximize conversion efficiency.