Search results for "Refractive index"
showing 10 items of 332 documents
Laser wavelength effects on the refractive index change of waveguides written by femtosecond pulses in silica glasses
2018
We investigate the influence of two fs-laser wavelengths (343 and 800 nm) on the induced refractive index change (Δn) of waveguides written in silica materials. Results show that Δn is higher for waveguides photo-inscribed with UV photons.
Real-time and low-cost sensing technique based on photonic bandgap structures
2011
[EN] A technique for the development of low-cost and high-sensitivity photonic biosensing devices is proposed and experimentally demonstrated. In this technique, a photonic bandgap structure is used as transducer, but its readout is performed by simply using a broadband source, an optical filter, and a power meter, without the need of obtaining the transmission spectrum of the structure; thus, a really low-cost system and real-time results are achieved. Experimental results show that it is possible to detect very low refractive index variations, achieving a detection limit below 2 x 10(-6) refractive index units using this low-cost measuring technique. (C) 2011 Optical Society of America[
Blue Moon: Is This a Property of Background Aerosol?
2010
Stellar extinction measurements made at three astronomical observatories showed that on ~50% of the nights the extinction due to aerosol light scattering increased rather than decreased with increasing wavelength (anomalous extinction) for wavelengths close to 500 nm. This extinction behavior is analyzed in this paper and limits are established for the aerosol characteristics necessary for this phenomenon to exist, including geometric standard deviations, imaginary part of refractive index, mean radius, and gaseous NO(2).
Absorbing anisotropic and gyrotropic slab between crossed polarizers in parallel light
1980
When a birefringent slab is rotated between two crossed polarizers, the four maxima and four minima of the transmitted intensity occur, as known, at every π/4 radians. If the slab is also optically active, the maxima and minima are arranged in other patterns that may be grouped according to the number of extrema met in one complete turn of the slab: four or eight. All the possible patterns are classified and each is related to some peculiarity of the complex refractive index of the slab.
Modeling of the photorefractive nonlinear response in Sn_2P_2S_6 crystals
2007
We develop a theory of the photorefractive nonlinear response for Sn2P2S6 crystals. The theory incorporates two types of charge carrier (optically active and passive), provides explicit expressions for the characteristic buildup-relaxation rates and gain factors, explains naturally a big variety of accumulated experimental data, and facilitates characterization-optimization of this important nonlinear material.
Role of dispersion on zero-average-index bandgaps
2009
We consider periodic multilayers combining ordinary positive index materials and dispersive metamaterials with negative index in some frequency ranges. These structures can exhibit photonic bandgaps which, in contrast with the usual Bragg gaps, are not based on interference mechanisms. Changing the dispersion models for the constituent metamaterial, we investigate its role in the production of zero-average-index bandgaps. In particular, we show the effect of each constitutive parameter on both bandgap edges. Finally, we give some approximated analytical expressions in terms of average parameters for the determination of the upper and lower limits of the zero-average refractive-index bandgap…
Impact of the scattering coefficient of scintillation crystals (LYSO and LSO) on depth of interaction resolution
2008
Intrinsic parameters in scintillation crystals play a crucial role in the measured spatial and energy resolutions. In many cases the measurement of these intrinsic parameters is difficult to be carried out or even there are parameters that need a specific setup to be measured directly, e.g. the intrinsic light yield and the absorption and scattering coefficients. These uncertainties in the parametrization of the characteristics of the scintillation crystals make it quite difficult to evaluate the quality and characteristics of the scintillation crystals and their impact on the resolutions. Results of measurements of depth of interaction and its resolutions for three different scintillation …
Peculiarities of coherent optical oscillation in Sn_2P_2S_6 crystals
2010
We show analytically and numerically that the unusual photorefractive nonlinear response of Sn2P2S6 crystals leads to a variety of new features of coherent optical oscillation. In addition to the explanation of the known peculiarities, new features are predicted.
Resolution enhancement in quantitative phase microscopy
2019
Quantitative phase microscopy (QPM), a technique combining phase imaging and microscopy, enables visualization of the 3D topography in reflective samples, as well as the inner structure or refractive index distribution of transparent and translucent samples. Similar to other imaging modalities, QPM is constrained by the conflict between numerical aperture (NA) and field of view (FOV): an imaging system with a low NA has to be employed to maintain a large FOV. This fact severely limits the resolution in QPM up to 0.82λ/NA, λ being the illumination wavelength. Consequently, finer structures of samples cannot be resolved by using modest NA objectives in QPM. Aimed to that, many approaches, suc…
m-bonacci metamaterial multilayers: location of the zero-average index bandgap edges
2009
We examine quasiperiodic multilayers arranged in m-bonacci sequences, which combine ordinary positiveindex materials and dispersive metamaterials with negative index in a certain frequency range. When the volume-averaged refractive index of the nonperiodic multilayer equals zero, the structure does not propagate light radiation and exhibits a forbidden band. We identify some analytical expressions to determine the upper and lower limits of the above zero-average refractive-index bandgap. We recognize that these limits are not explicitly dependent on the geometrical parameters of the stack of layers. © 2009 Optical Society of America. Fil: Monsoriu, J.A.. Universidad Politécnica de Valencia;…