Search results for "Refraction"
showing 10 items of 200 documents
Magnification of the retinal image through an intraocular Galilean telescope
2010
The intraocular Galilean telescope is a good solution for incrementing the visual capabilities of patients with age-related macular degeneration. Nevertheless, some problems arise with the use of the intraocular telescopes available at present; these problems are originated by two main factors: the use of the same power values for the lenses in all types of eyes and the fact that the values of the distance between lenses into the eye are not the most suitable ones. As a result, a high residual refraction is produced in many implanted eyes. We propose a method for predicting outcomes in order to select patients for this technique and, moreover, for choosing the optimum power for the positive…
Repeatability of whole-cornea measurements using a new swept-source optical coherence tomographer
2020
Purpose: The aim of this study was to evaluate the repeatability of several corneal parameters provided by a high-resolution swept-source optical coherence tomographer (SS-OCT). Methods: One eye from each of 74 patients was measured five times consequently using the ANTERION SS-OCT. The following corneal parameters were analyzed: average, steep and flat keratometry (K), astigmatism for anterior, posterior and total at 3-mm, average K and astigmatism at 6-mm, anterior and posterior eccentricity, higher-order aberrations (HOA) and spherical aberration ([Formula: see text]), and anterior and posterior best-fit sphere at 8-mm. The intrasubject standard deviation (Sw), coefficient of variation (…
Left-handed metamaterial coatings for subwavelength-resolution imaging
2012
We report on a procedure to improve the resolution of far-field imaging by using a neighboring high-index medium that is coated with a left-handed metamaterial. The resulting plot can also exhibit an enhanced transmission by considering proper conditions to retract backscattering. Based on negative refraction, geometrical aberrations are considered in detail since they may cause a great impact in this sort of diffraction-unlimited imaging by reducing its resolution power. We employ a standard aberration analysis to refine the asymmetric configuration of metamaterial superlenses. We demonstrate that low-order centrosymmetric aberrations can be fully corrected for a given object plane. For su…
Nonlinear refraction and absorption of spectrally tuneable picosecond pulses in carbon disulfide
2021
Abstract We analyze the spectral dependence of the nonlinear refractive index and nonlinear absorption coefficient of carbon disulfide (CS2) in the spectral range of 400–1100 nm using picosecond laser pulses. An increase of the nonlinear refractive index of CS2 at the shorter wavelength region compared with the near infrared region (9 × 10−14 cm2 W−1 (λ = 700 nm) and 4 × 10−14 cm2 W−1 (λ = 1000 nm), respectively) follows by a decrease of this parameter at the wavelengths below 600 nm. We compare the spectral dependences of the lower- and higher-order nonlinear absorption coefficients in carbon disulfide. The three-photon absorption coefficient was found to be maximal at λ = 1000 nm (β3PA = …
Nonlinear Optical Characterization of InP@ZnS Core-Shell Colloidal Quantum Dots Using 532 nm, 10 ns Pulses
2021
InP@ZnS core-shell colloidal quantum dots (CQDs) were synthesized and characterized using the z-scan technique. The nonlinear refraction and nonlinear absorption coefficients (γ = −2 × 10−12 cm2 W−1, β = 4 × 10−8 cm W−1) of these CQDs were determined using 10 ns, 532 nm pulses. The saturable absorption (β = −1.4 × 10−9 cm W−1, Isat = 3.7 × 108 W cm−2) in the 3.5 nm CQDs dominated at small intensities of the probe pulses (I ≤ 7 × 107 W cm−2) followed by reverse saturable absorption at higher laser intensities. We report the optical limiting studies using these CQDs showing the suppression of propagated nanosecond radiation in the intensity range of 8 × 107–2 × 109 W cm−2. The role of nonline…
Solving ultrasonic ray tracing in parts with multiple material layers through Root-Finding methods
2022
Ultrasonic testing has been used for material analysis and inspection since 1930's. Nevertheless, the applicability of ultrasonic waves to new complex cases is still growing, thanks to the availability of powerful electronics and software. However, the complication that slows down the deployment of ultrasonic inspection to geometric complex parts and structures arises from the wave refraction phenomenon. A clear understanding of the ultrasound wave propagation, impacted by refractions, is crucial to interpret the data obtained from the inspection of multi-layered/multi-medium test subjects as it is not always possible to assume that mechanical waves travel in straight lines. This work prese…
The effect of fractal contact lenses on peripheral refraction in myopic model eyes.
2014
Purpose: To test multizone contact lenses in model eyes: Fractal Contact Lenses (FCLs), designed to induce myopic peripheral refractive error (PRE). Methods: Zemax ray-tracing software was employed to simulate myopic and accommodation-dependent model eyes fitted with FCLs. PRE, defined in terms of mean sphere M and 90–180 astigmatism J180, was computed at different peripheral positions, ranging from 0 to 35 in steps of 5, and for different pupil diameters (PDs). Simulated visual performance and changes in the PRE were also analyzed for contact lens decentration and model eye accommodation. For comparison purposes, the same simulations were performed with another commercially available conta…
The stenopaeic slit: an analytical expression to quantify its optical effects in front of an astigmatic eye.
2001
The stenopaeic slit is a trial case accessory used in subjective refraction, especially when high astigmatism is present. In spite of its simplicity, the effect of the slit when it is not oriented along one of the principal meridians of the examined eye is difficult to predict, even in terms of classical geometrical optics. In this paper, the optical principles of the slit are considered with full details in the theoretical framework of the dioptric power space. An analytical expression to obtain the residual refractive error when a stenopaeic slit is placed in front of an astigmatic eye at any orientation is deduced. In the light of these results, some aspects of the clinical procedure are…
Wavelet correlation filter for wide-angle seismic data
2002
A new filtering technique for single-fold wide-angle reflection/refraction seismic data is presented. The technique is based on the wavelet decomposition of a set of adjacent traces followed by coherence analysis. The filtering procedure consists of three steps. In the first, a wavelet decomposition of traces into different detail levels is performed. In the second, the coherence attributes for each level are evaluated by calculating cross-correlation functions of detail portions contained in a space–time moving window. Finally, the filtered traces are obtained as a weighted reconstruction of the trace details. Each weight is obtained from the coherence-attributes distribution estimated in …
Deep-rooted “thick skinned” model for the High Atlas Mountains (Morocco). Implications for the structural inheritance of the southern Tethys passive …
2006
A re-interpretation of the deep structure of the High Atlas is presented through integration of geophysical and geological data, highlighting the architectural significance of the southern Tethys palaeomargin. Previous crustal models suggest the occurrence of a flat intra-crustal detachment at a depth of � 20 km, a zone where surface thrusts merge and below which the lower High Atlas crust appears continuous. However, within this study seismic refraction data, electrical resistivity surveys and gravity modelling all appear to detect a jump in crustal thickness between the High Atlas and the northern plains. We interpret these data as penetration by thrusts within the ‘‘South-Atlasic fault’’…