Frustration Of Total Internal Reflection Research Articles

Sensitivity enhancement of plasmonic grating in the local field.

A plasmonic grating consisting of parallel gold or silver nanowires on the glass substrate is an excellent sensor for refractive index measurement of a gas or liquid medium. We suggest measuring the local field in a gap between the wires to increase the sensitivity. The local electric field contains more information on the environment since it includes the evanescent waves. Calculation by the boundary element method confirms a substantial improvement of sensitivity owing to a sharp cusp-like gap resonance in the angular dependence. The local field measurement under the frustration of total internal reflection has promising prospects for the development of modern biomedical and chemical sensors.

Scattering by multiple cylinders located on both sides of an interface

The solution for scattering by multiple parallel infinite cylinders located in adjacent half spaces with dissimilar refractive index is presented in this paper. The incident radiation is an arbitrarily polarized plane wave propagating in the upper half space in the plane perpendicular to the axis of the cylinders. The formulation of the electromagnetic field vectors utilized Hertz potentials that are expressed in terms of an expansion of cylindrical wave functions. It accounts for the near-field multiple scattering, Fresnel effect at the interface, and interaction between cylinders in both half spaces. Analytical formulas are derived for the electromagnetic field and Poynting vector in the far-field. The present solution provides the theoretical framework for deducing the solutions for scattering by cylinders located on either side of an interface irradiated by a propagating or an evanescent incident wave. Deduction of these solutions from the present formulation is demonstrated. Numerical results are presented to illustrate the frustration of total internal reflection and scattering of light beyond the critical angle by nanocylinders located in either or both half spaces.

Optimization of an Optical Test Bench for Tire Properties Measurement and Tread Defects Characterization

Tire characteristics and behavior are of great importance in vehicle dynamics since the forces transmitted in the tire-road contact are the main contributors to global vehicle performance. Several research groups have focused on the study and modeling of tires. Some of the most important factors that need to be known are tread characteristics and pressure distribution in the tire-ground contact patch. In this work, a test bench has been used to adequately determine the aforementioned factors. The measurement principle of the test bench is the frustration of total internal reflection (FTIR) of light. It makes use of a laterally illuminated glass on which the tire leans. An interposed plastic interface between them causes the reflection of light. Finally, a video camera captures the bright image formed through the glass. The brightness level in each pixel of the image is related to existing normal pressure. A study of the parameters that affect the test bench calibration such as type of interface material used, diffuse light, hysteresis, creep and transverse light absorption is performed. Experimental tests are conducted to relate tire inflation pressure and camber angle to the pressure distribution. Furthermore, the test bench is used to detect and evaluate the influence of defects in the tire on the contact pressures.

Frustration of total internal reflection by a hidden nanowire

A metallic wire embedded in the dielectric substrate leads to frustration of the total internal reflection at the interface between dielectric and free space. The scattering by a gold cylinder is studied in order to exploit the light for hidden objects optical diagnostics. The p-wave incidenting by the angle close to total reflection with the frequency near plasmonic resonance is treated by the modified boundary elements method. The magnetic and electric fields at the interface are calculated. The scattering diagrams are found in near and far field.

Transparent superhydrophobic surfaces for applications of controlled reflectance

This work involves a new optical application for transparent superhydrophobic materials, which enables low-energy optical contact between a liquid and solid surface. The new technique described here uses this surface property to control the reflectance of a surface using frustration of total internal reflection. Surface chemistry and appropriate micro-scale and nano-scale geometries are combined to produce interfaces with low adhesion to water and the degree to which incident light is reflected at this interface is controlled by the movement of water, thereby modifying the optical characteristics at the interface. The low adhesion of water to superhydrophobic surfaces is particularly advantageous in imaging applications where power use must be minimized. This paper describes the general approach, as well as a proof-of-principle experiment in which the reflectance was controlled by moving a water drop into and out of contact with a superhydrophobic surface by variation of applied electrostatic pressure.

OPTICAL HYDROGEN SENSOR WITH INCREASED SENSITIVITY BASED ON TUNGSTEN OXIDE FILM

A computer simulation of the effect of frustration of total internal reflection in the region of the interface between glass and WO3 film with thin catalyst (Pt, Pd) layer by hydrogen with different concentration in the hydrogen-air mixture has been performed. A design of optical hydrogen sensor has been developed, and its laboratory model has been made on the basis of this effect with high hydrogen sensitivity in the range of low hydrogen concentration in the hydrogen-air mixture (down to under 0.01vol. % [H2]). The substantial increase in the hydrogen sensitivity of the sensor has been achieved through the multiple reflection by the glass/WO3 interface of IR light with 940 nm wavelength in its propagation through glass light guide.

An optical tire contact pressure test bench

An optical tire contact pressure test bench developed by the IMMa group is described. The measurement system is based on the frustration of total internal reflection (FTIR) of light. The test bench allows performing normal pressure distribution and patch contact shape measurements on passenger car tires. The system is based on the use of a laterally illuminated glass on which the tire leans. Between them a plastic interphase is located that will cause the FTIR of light. A video camera catches the formed shining image through the glass. The brightness level in each pixel of the image can be related to the existing normal pressure. The study of the contact patch provided by the bench makes it possible to characterize tire behaviour under different loading states, inflation pressure, tire defects and toe and camber angles. The bench incorporates a computerized load and control system of the tire operation parameters, an image acquisition module and a data acquisition system that allow monitoring and acting on the experimental variables of interest in the tests such as load on the tire and environmental conditions. A supporting mechanical system incorporated to the bench allows providing the tire with variable toe and camber angles. From the images obtained with this system, the maximum normal pressure points, total force, size and shape of the patch can be determined, which are related to the tire-use conditions. As an application example, results that show the patch size and shape under different load and tire inflation pressures are presented. A further application, which is the use of the system for the detection and study of defective tires is also presented.

Controlled frustration of total internal reflection by electrophoresis of pigment particles

A model based on geometrical optics has been developed to describe the photometric observations associated with a novel method to control the reflectance of a surface. In this new reflectance modulation approach, electrophoresis of pigment particles is used to absorb light reflected by total internal reflection (TIR). The pigment particles are sufficiently small that they substantially do not scatter light, but rather they modify the effective refractive index at the reflection interface. An incident light ray interacting with this modified effective index is attenuated in a spectrally selective manner. Although frustrated TIR has been understood and used in various applications for some time, in this case it is used to substantially modify the color of the reflected light, which to our knowledge has not been previously reported. A numerical model of the pigment particle distribution has been developed to describe the observations.

Modulation of retroreflection by controlled frustration of total internal reflection

Retroreflective images are useful in outdoor application for which high legibility is required both during the day and in response to vehicular illumination. To date, all variable message retroreflective images have employed mechanical shutters as the switching mechanism. As an alternative, we propose a method for switching the total internal reflection effect used in retroreflectors by means of pneumatic actuation of surface treated polydimethylsiloxane gel. This approach is both effective and compatible with current large-scale manufacturing methods.

Liquid laser cavities and waveguides. III. Radiation coupling-out and fluorescence under uniform excitation. 'Evapolators'

An investigation was made of laser radiation coupling-out from totally reflecting closed liquid cavities by local frustration of total internal reflection with the aid of internal water spheres and external contact with a substrate or a prism. A rotating drop of ethanol containing rhodamine B in an envelope of liquid C8F18 generated laser radiation with a divergence of several angular degrees and an efficiency up to 5% relative to the excitation energy. A transparent drop of ethanol with rhodamine B, suspended in air, and subjected to uniform pumping was used to determine the depth of the zone in which lasing took place in a liquid cavity. An increase in the integral (during the pump time) fluorescence energy from a selected internal part of this drop, which did not participate in lasing, on increase in the excitation flux was in agreement with the expectations and it began to fall at high pump intensities. Characteristics of oscillations in immiscible liquids which evaporated in an evaporator — oscillator ('evapolator') were discussed.

Scanning of a laser beam and purification of materials through the use of light-induced particle drift in semiconductors

The light-induced drift of electrons, light-absorbing impurities, and defects in II-VI semiconductors is investigated experimentally, along with some potential practical applications of the phenomenon. It is shown that the light-induced drift of electrons induces a very pronounced change in the refractive index, |Δn|∼0.01, and can be used to implement effective scanning of nanosecond and picosecond laser pulses through frustration of total internal reflection. The light-induced drift of absorbing particles increases their density in the surface layer of the crystals, and this effect can be exploited in semiconductor technology.

Measurement of surface dew by optical sensor

The present work describes the design of a purely optical sensor for the detection of surface dew. The operation of the device is based on the frustration of total internal reflection. Constructions with conventional optical elements and with a holographic optical element (HOE) are discussed. The HOE is recorded by He-Ne laser and the diffraction efficiency is measured for s and p polarizations of the reconstructing beam. Also, the sensor characteristic for various dew densities of the sensitive surface is obtained theoretically and is proved experimentally. The sensor may be useful for isolation control of high-voltage devices.

Observation of optical waveguides by using a photon scanning tunneling microscope

The photon scanning tunneling microscope (PSTM) is based on the frustration of total internal reflection by the apex of an optical fiber placed near the surface of reflection. It has so far been used to obtain topographic information. This article shows that it also allows one to reach local variations of the refractive index of the sample. The PSTM, like many local probes, is operated on a constant intensity level. In that case a theoretical analysis based on a simple model shows that a change of the refractive index can actually be seen with the PSTM. The authors find that the corrugation height depends on the distance between the tip and the sample surface. The local refractive index of microguides diffused in glass has been studied experimentally with the PSTM. Relative variations in the order of 10-3 have been observed.

Gas laser with a phase anisotropy of reflection controlled by frustration of total internal reflection

Theoretical and experimental studies were made of the feasibility of controlling the mode spectrum of a gas laser with a phase anisotropy of reflection. It was found that when total internal reflection was replaced by external reflection from the boundary with a strongly absorbing medium, an effective change in the phase anisotropy occurred. This may be used for wide-range control of the laser radiation spectrum and highly sensitive measurements of spatial displacements of the surfaces.

Planar and finger-shaped optical tactile sensors for robotic applications

Progress is described regarding the development of optical tactile sensors specifically designed for application to dexterous robotics. These sensors operate on optical principles involving the frustration of total internal reflection at a waveguide/elastomer interface and produce a grey-scale tactile image that represents the normal (vertical) forces of contact. The first tactile sensor discussed is a compact, 32*32 planar sensor array intended for mounting on a parallel-jaw gripper. Optical fibers were employed to convey the tactile image to a CCD camera and microprocessor-based image analysis system. The second sensor had the shape and size of a human fingertip and was designed for a dexterous robotic hand. It contained 257 sensing sites (taxels) distributed in a dual-density pattern that included a tactile fovea near the tip measuring 13*13 mm and containing 169 taxels. The design and construction details of these tactile sensors are presented, in addition to photographs of tactile imprints. >