Design of a Surface Plasmon Resonance CO Sensor.

Carbon monoxide (CO) is a highly toxic gas, which can cause death if it is inhaled in small quantities for a long time or in large quantities for a short time. Since this gas can be lethal, it is essential to detect it from minute to large concentrations. Our study consists of the design of a superficial plasmonic resonance (SPR) CO sensor of tiny dimensions which is capable of giving an immediate response at different concentrations. It is designed to work at different heights above sea level since the refractive index of this gas depends on a mixture with air and the air pressure. Due to its low weight and tiny dimensions, it is ideal for space travel or on airplanes. The results show a high resolution and sensitivity (~10-5 RIU of resolution and a sensitivity of 13.51-81.26 RIU-1).

A Continuous Liquid-Level Sensor for Fuel Tanks Based on Surface Plasmon Resonance.

A standard problem in large tanks at oil refineries and petrol stations is that water and fuel usually occupy the same tank. This is undesirable and causes problems such as corrosion in the tanks. Normally, the water level in tanks is unknown, with the problems that this entails. We propose herein a method based on surface plasmon resonance (SPR) to detect in real time the interfaces in a tank which can simultaneously contain water, gasoline (or diesel) and air. The plasmonic sensor is composed of a hemispherical glass prism, a magnesium fluoride layer, and a gold layer. We have optimized the structural parameters of the sensor from the theoretical modeling of the reflectance curve. The sensor detects water-fuel and fuel-air interfaces and measures the level of each liquid in real time. This sensor is recommended for inflammable liquids because inside the tank there are no electrical or electronic signals which could cause explosions. The sensor proposed has a sensitivity of between 1.2 and 3.5 RIU(-1) and a resolution of between 5.7 × 10(-4) and 16.5 × 10(-4) RIU.

Retinal-image quality and contrast-sensitivity function in age-related macular degeneration.

PURPOSE: In this article, retinal-image quality and contrast sensitivity were measured in 25 patients with age-related macular degeneration (ARMD) and 15 patients with normal retinal health. MATERIALS AND METHOD: Retinal-image quality was evaluated with an objective device based on the double-pass technique, and for visual performance we measured the contrast-sensitivity function. RESULTS: The results from double-pass device revealed the Strehl ratio to be significantly (p < 0.0001) lower for the ARMD group with a 54.3% reduction for 3 mm pupil size and a 46.9% reduction for 4 mm. Contrast-sensitivity function for ARMD subjects was also significantly lower than for the control group (p < 0.05) with a 38.6% reduction. CONCLUSIONS: Patients affected with ARMD showed poorer retinal-image quality and visual performance than normal subjects. The use of objective devices based on the double-pass technique could be useful for the accurate description of the retinal-image quality of ARMD eyes, in which retinal scattering is significantly increased.

Optical image quality and visual performance for patients with keratitis.

PURPOSE: To evaluate the optical image quality, using 2 optical devices (an aberrometer and a double-pass device), and visual performance [contrast sensitivity function (CSF)] in patients with keratitis and after resolution of the disease. METHODS: Twenty subjects with keratitis (18 patients with unilateral keratitis and 2 patients with bilateral keratitis) were included in this study. We also took measurements in healthy fellow eyes for comparison. Ten patients were studied before and after the resolution of keratitis. Objective data were gathered by aberrometry (ocular higher order, spherical, and coma aberrations) and the Strehl ratio, a parameter derived from the double-pass device that included information on diffraction, ocular aberrations, and scattering. The CSF was also measured for all the patients. RESULTS: Ocular higher order, spherical, and coma aberrations in keratitis eyes were significantly (P < 0.05) higher than those in healthy fellow eyes. The Strehl ratio indicates a worse optical quality for keratitis eyes being significantly (P < 0.05) lower than the Strehl ratio for healthy fellow eyes. CSF for keratitis eyes was also significantly lower than that for the healthy eyes (P < 0.05). Data for keratitis eyes after the resolution of the disease showed a significant increase in the optical function and visual performance but, after treatment, continued to suffer significant (P < 0.05) impairment in the optical quality of the affected eyes compared with the healthy fellow eyes. CONCLUSIONS: Devices to measure optical image quality and the CSF enable the characterization of the optical quality and visual performance in patients with keratitis, showing a significant decline in optical quality and visual performance during keratitis and an improvement after the resolution of the pathology.

Stability and reproducibility of radiometric properties of light curing units (LCUs). Part I: QTH LCUs.

The present study, divided into two parts, analyses the stability and reproducibility of the spectral and energy emission of the present light-curing units (LCUs), quartz tungsten halogen (QTH) and light-emitting diodes (LEDs). In part I, QTH LCUs were studied. The results showed that the QTH LCUs studied presented high stability and reproducibility in terms of their spectral emission with VAF (variance accounting for) values from the Cauchy-Schwarz inequality, all close to 100%. With respect to the energy stability, the QTH LCUs studied can be considered stable under practical clinical conditions, although for some devices the initial irradiance value is critical. This result should be taken into account in those works which is researched in polymerization kinetics of dental materials as well as in clinical practice.

Stability and reproducibility of radiometric properties of light curing units (LCUs). Part II: LED LCUs.

The present work is the second part of a study on the stability and reproducibility of the energy and spectral emission of some light curing units (LCUs). In this part, Part II, LED LCUs were investigated. Results revealed that these devices presented high stability and reproducibility in terms of their spectral emission, with values of VAF (variance accounting for) coefficient calculated from the Cauchy-Schwarz inequality all close to 100%. With respect to energy stability, the LED LCUs presented energy stability except for the third-generation LED LCUs which have several LEDs. For these devices, the law of reciprocity was not fulfilled as irradiance was not constant over exposure time. This result should be taken into account both in works examining the polymerization kinetics of dental materials as well as when these LED LCUs are used in clinical practice.

Planar dielectric waveguides in rotation are optical fibers: comparison with the classical model.

A novel and simpler method to calculate the main parameters in fiber optics is presented. This method is based in a planar dielectric waveguide in rotation and, as an example, it is applied to calculate the turning points and the inner caustic in an optical fiber with a parabolic refractive index. It is shown that the solution found using this method agrees with the standard (and more complex) method, whose solutions for these points are also summarized in this paper.

Correction factor for ablation algorithms used in corneal refractive surgery with gaussian-profile beams.

We provide a correction factor to be added in ablation algorithms when a Gaussian beam is used in photorefractive laser surgery. This factor, which quantifies the effect of pulse overlapping, depends on beam radius and spot size. We also deduce the expected post-surgical corneal radius and asphericity when considering this factor. Data on 141 eyes operated on LASIK (laser in situ keratomileusis) with a Gaussian profile show that the discrepancy between experimental and expected data on corneal power is significantly lower when using the correction factor. For an effective improvement of post-surgical visual quality, this factor should be applied in ablation algorithms that do not consider the effects of pulse overlapping with a Gaussian beam.

Corneal asphericity after refractive surgery when the Munnerlyn formula is applied.

We deduce a mathematical equation for corneal asphericity after refractive surgery when the Munnerlyn formula is used. For this, an analytical least-squares procedure is used. The equation explains the discrepancies found by different authors when the Munnerlyn formula or its paraxial approximation is used. Equations for corneal asphericity deduced here may be of clinical relevance, for example, in studying quantitatively the role of different factors (decentration, type of laser, optical role of the flap, wound healing, biomechanical effects, technical procedures) during corneal ablation.