Search results for "Refractive index"
showing 10 items of 332 documents
Self Calibrating Nano-Ruler
2012
The aim of a nanoruler is to measure distances on a length scale in the order of nanometers. This concept can be realized by two plasmonic nanoparticles (usually spheres), which are placed within a short distance to each other. Since the plasmon modes of both particles are coupled, they influence each other along the interparticle axis (i.e. longitudinal plasmon mode, resulting in a shift of the resonance wavelength compared to the single particle. Because the resulting resonance wavelength depends on the interparticle distance, the spectral investigation of such a dimer allows the determination of the interparticle distance.
Fabrication and characterization of tuned Gaussian mirrors for the visible and the near infrared
1988
A thin-film technique has been developed for vacuum fabrication of mirrors with Gaussian reflectivity profiles. Samples with diameters from 2 to 8 mm and assigned maximum reflectivities for visible or near-IR wavelengths have been made and their optical properties evaluated. By properly choosing both the geometry of the evaporation source and the masking system, one can obtain quasi-Gaussian or super-Gaussian reflectivity profiles.
Measurement of UV-induced absorption and scattering losses in photosensitive fibers
2018
UV-assisted fabrication of gratings using photosensitive fibers is a well-established technique, based on the UV-induced permanent modification of the refractive index of the fiber material. As a result, the absorption coefficient is also changed. Here, we exploit the thermal sensitivity of whispering gallery mode resonances of the fiber itself to measure the profile of the heating along an irradiated fiber versus the input power and for different UV radiation intensities. Our technique allows discriminating between the absorption and scattering contributions to the overall losses, by comparing the results obtained with our technique with direct transmission measurements. Different photosen…
Optical determination of the oxygen content of YBa2Cu3O6+x thin films by IR reflectance and transmittance measurements
2001
Abstract Recent studies of the optical properties of YBa2Cu3O6+x (YBCO) single crystals by several authors have shown that the optical conductivity in the infrared spectral region is a sensitive function of the oxygen content of the samples. Infrared spectroscopy thus offers a possibility for oxygen concentration analysis and is an alternative to other methods such as (i) the X-ray determination of the length of the c-axis and (ii) spectroscopic ellipsometry at an electronic transition band centered around 4.1 eV whose strength decreases with increasing oxygen content. We explore the applicability of the IR optical method for the case of YBCO thin films of about 300 nm thickness which are e…
Core-clad phosphate glass fibers for biosensing
2019
Recently, a phosphate glass with composition 20 CaO-20 SrO-10 Na2O-50 P2O5 (mol%) was found to have good potential as a biomaterial and to possess thermal properties suitable for fiber drawing. This study opened the path towards the development of fully bioresorbable fibers promising for biosensing. In the past, this phosphate glass with CeO2 was found to increase the refractive index and the glass stability. Therefore, a new SrO-containing glass was prepared with 1 mol% of CeO2 and core fibers were drawn from it. A core-clad fiber was also processed, where the core was a Ce-doped glass and the clad undoped, to allow for total internal reflection. The mechanical properties of the core and c…
Temperature dependence of refractive index and absorption coefficient of GaSe at 633 nm
1995
Abstract Measurements of the ordinary refractive index and the absorption coefficient ( E /t] to c axis ) of gallium selenide at 633 nm, in the temperature range [20,100] °C, are reported. Useful analytical approximations obtained after a least squares fitting process are provided, as well. These results are basic for any theoretical model of nonlinear and bistable optical devices based on GaSe.
<title>Holographic recording of subwavelength structures in amorphous chalcogenide thin films</title>
2005
Holographic recording of surface-relief and refiactive-index-modulated gratings with a period ranging from 0.15 to 1 μm in thin amorphous chalcogenide films of As-S-Se and As2S3 is studied. The profile of the surface-relief gratings is measured by atomic force microscopy. By structuring the As-S-Se films with the subwavelength-period surface-relief gratings their reflectivity is decreased from 25-30% to less than 2%. In the refractive-index-modulated As2S3 films polarization effects are revealed. It is shown that the angular selectivity of the holographic recording in amorphous chalcogenide thin films can be substantially improved by decreasing the grating period.© (2005) COPYRIGHT SPIE--Th…
<title>Application of amorphous chalcogenide thin films in optical recording technologies</title>
2005
A review of the recent advances and developments in the practical application of amorphous chalcogenide materials is presented, focusing special attention to holography and lithography. The main functional principles and practical application of amorphous chalcogenide photoresists for production of the embossed rainbow holograms and holographic optical elements are discussed. The laser interference lithography can be used as a low-cost method for the exposure of large surfaces with regular patterns like subwavelength-gratings and microsieves. The surface-relief and reftactive-index modulated gratings with a period of about 50 nm and less can be fabricated by immersion holographic method. Th…
Model of holographic recording in amorphous chalcogenide films using subband-gap lightat room temperature
1997
The subband-gap light holographic recording in amorphous as-evaporated ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ films at room temperature is experimentally studied. Properties are considerably different from those of usual holographic recording based on the band-gap light induced structural changes. The most important characteristic features of this nonpermanent recording include photoinduced refractive index increase, weak photobleaching, the absence of the photoinduced thickness changes, light polarization dependence, large exposures, holographic grating shifts during the exposure and a peculiar two maxima spatial frequency response. The first order diffraction efficiency up to 4.1% is achie…
Novel plasmonic sensor design using plasmon-induced transparency
2010
We introduce a novel sensor concept in the field of plasmonics, namely plasmon-induced transparency sensors. These sensors combine localized particle plasmon resonances with extremely small sensing volume with excellent sharp spectral resonances that show a good respose to refractive index changes of the surrounding environment. The principle is based on the plasmonic analog of electromagnetically induced transparency (EIT) between a radiative dipole and a nonradiative quadrupole antenna. This effect yields a spectrally narrow resonance within a broad localized particle plasmon resonance in the near-infrared spectral region [1, 2]. Using deposition of biotin and streptavidin, we demonstrate…