Showing papers on "Total internal reflection published in 1995"

Evanescent scanning of biochemical array

Abstract: An apparatus for detecting a target substance in a pixel array is provided. The apparatus has a light source to emit a light suitable for exciting the target substance in the array, a total internal reflection (TIR) member, and a light detector. The TIR member has a TIR surface on which the array is located. The light from the light source passes into the TIR member and is reflected by the TIR surface. The array is within an evanescent field region at the TIR surface. The light detector is adapted to detect light emitted from the array as a result of evanescent excitation of the target substance.

Thermal optical switches for light

Abstract: A thermal optical switching cell has a channel of either gas or boilable liquid that crosses an optical waveguide at a forty-five degree angle Two or more appropriately placed heaters use the water/steam/dry states of thermal ink jet technology to quickly insert, or extract, boilable liquid respectively into, or from, the channel The boilable liquid has an index of refraction close to that of the guide In the wet state, the channel contains the liquid and nearly all the light of the incoming guide traverses the liquid along the axis of the guide In the dry state, the channel contains gas Total internal reflection (TIR) occurs and light is directed at right angles away from the axis of the incoming channel Adding a second waveguide, perpendicular to, and intersecting the first waveguide at the channel, forms a cross-bar switch These liquid switching cells toggle between the wet and dry states No power is required to hold the switch in the most recent state A monitoring signal is described that can be used to determine the state of the switch The dry state of these cells is totally internally reflecting The wet state, however, is transmissive with a small, but objectionable, amount of reflection A push-pull optical circuit is formed using paired cells and at least one TIR mirror One of the cells of the circuit is always in the TIR, state to provide good isolation This circuit has the property of reporting the state of the switch-pair so that a fault can be detected If a fault is detected, repeated activation pulses can be applied to force liquid into the correct places to maintain proper operation of the circuit

Refractive index measurement of absorbing and turbid fluids by reflection near the critical angle

Abstract: A method is described for measuring the specular optical reflectance R( phi ) of the interface between a fluid and a glass prism, the incident and reflected light being in the glass, and the angle of incidence phi being varied about the critical angle. Transparent, absorbing and some turbid fluids give R( phi ) dose to theoretical predictions, and experimental reflectance data are analysed to give the real (n') and imaginary (n") refractive indices of the fluid. Other turbid fluids gave R( phi ) data that differed strongly from theoretical expectation. This is attributed to heterogeneity of the fluid on the optical wavelength scale, and problems of refractometry for such fluids are discussed.

Ray chaos and Q spoiling in lasing droplets.

Abstract: The highest Q optical resonators known are dielectric microspheres in which the high Q modes are created by total internal reflection of light circulating just inside the surface of the sphere[1, 2]. These high Q modes are referred to as “whispering gallery” (WG) modes or alternatively as “morphology-dependent resonances” (MDR’s) [2]. If the dielectric is a liquid droplet containing an appropriate dye then the droplet acts as a high Q micro-resonator to support lasing action of the dye when optically pumped [3]. The resonance properties of an ideal spherical dielectric, for which the wave equation separates, are described by Mie theory where the quasi-modes are the product of spherical Bessel functions jl(nkr) (n is the index of refraction) and vector spherical harmonics [4]. The radial equation then contains a repulsive term l(l + 1)/r2 which is the analogue of the angular momentum barrier for light rays and an effectively attractive term associated with the higher index of refraction in the liquid. The combination of the attractive “well” represented by the dielectric and the repulsive angular momentum barrier gives rise to quasi-bound states of the effective potential near the rim of the droplets[4] for certain ratios of l to kR (k is the wavevector in vacuum, R the radius of the spherical droplet). In the ideal sphere these resonances are only broadened by evanescent leakage (“tunneling”), hence their enormous Q values.

Visor-display design based on planar holographic optics

Abstract: A method for designing and recording visor displays based on planar holographic optics is presented. This method can deal with the problem of recording-readout wavelength shift. The display system is composed of two holographic optical elements that are recorded on the same substrate. One element collimates the waves from each data point in the display into a plane wave that is trapped inside the substrate by total internal reflection. The other diffracts the plane waves into the eye of an observer. Because the chromatic dispersion of the first element can be corrected by the dispersion of the second, this configuration is relatively insensitive to source wavelength shifts. The method is illustrated by the design, recording, and testing of a compact holographic doublet visor display. The recording was at a wavelength of 458 nm, and readout was at 633 nm. The results indicate that diffraction-limited performance and relatively low chromatic dispersion over a wide field of view can be obtained.

Irradiance attachment for an optical fiber to provide a uniform level of illumination across a plane

Abstract: An irradiation attachment for an optical fiber (4) which provides an output of light that has a highly uniform intensity. The device includes a hollow spherical shell (1) having a diffusive reflective surface or target (11) supported (12) therein. Light is directed into the hollow spherical shell (1) so that it reflects off the diffusive reflective surface or target (11). The reflected light is internally reflected off the inner surface of the hollow spherical shell (1) several times before passing through an output aperture (8). As a result of the internal reflection within the hollow spherical shell (1), the light leaving the device has a highly uniform intensity. The device is particularly useful for photodynamic therapy.

Resonant cavities employing two dimensionally periodic dielectric materials

Abstract: The present invention provides a resonant cavity including a planar two-dimensional periodic dielectric structure which exhibits a photonic band gap and a defect in the periodic dielectric structure which results in an electromagnetic mode within the photonic band gap. The photonic band gap effects an in-plane spacial confinement of electromagnetic radiation generated within the structure. The electromagnetic radiation is vertically confined by total internal reflection.

A high-gain, compact, nonimaging concentrator: RXI

Abstract: The design procedure of a new nonimaging concentrator (called an RXI) is explained. Rays that impinge on the concentrator aperture, within the acceptance angle, are directed to the receiver by means of one refraction, one reflection, and one total internal reflection. The concentrator can be made as a single dielectric piece (in which the receiver is immersed) whose aspect ratio (thickness/aperture diameter) is close to 1/3. Ray-tracing analysis of a rotational symmetric RXI shows total transmissions of greater than 94.5% (no absorption or reflection losses are considered) when the acceptance angle of the incoming rays is small (<3°) and when the receiver area is the smallest possible (maximal concentration.)

Photorefractive surface waves.

Abstract: A laser beam propagating in a photorefractive crystal generates a refractive-index profile that deflects the beam to one side. This nonlinear deflection can be balanced by total internal reflection at the crystal surface to produce self-induced photorefractive surface waves. Theoretical and experimental evidence for this effect is given.

Light guide and liquid crystal display device using it

Abstract: On a light exit surface which is the first principal plane of a light guide, multiple projections are fabricated in specific rows. These projections have light exit surfaces and continuous multiple slopes, and are fabricated from optically identical materials having the same refractive index as the substrate of the light guide. The slope farthest from the light entry edge surface is formed as a light exit surface, i.e., a surface which breaks the conditions for the total reflection of the incident light. On the other hand, the slope nearest the light entry edge surface which is the total reflection surface is formed such that the incident light is totally reflected.

Method for measuring water diffusion in a coating applied to a substrate

Abstract: A method based on Fourier transform infrared-multiple internal reflection (FTIR-MIR) spectroscopy was developed for measuring the apparent diffusion coefficient of water in a coating applied to a substrate. The method requires an appliction of a coating of any thickness on an internal reflection element, which serves as the substrate, with the attachment of a water chamber to the coated specimen. Water is introduced to the chamber and FTIR-MIR spectra are collected automatically without disturbing the specimen or the instrument. The amount of water at the coating/substrate interface was determined using a model based on the theory of internal reflection spectroscopy. A mass-time curve for water at the interface is established, which provides the time-lag value, the time required for water to diffuse through the coating film and reach the interface. The diffusion coefficient (D) is then determined by the time-lag equation. For thick coating films (>25 μm), D may be estimated from the FTIR-MIR in situ intensity data only. The sensitivity of FTIR-MIR spectroscopy and the strong FTIR absorption of water molecules make this an ideal method for measuring the diffusivity of liquid water through a coating applied to a substrate

Angle measurement based on the internal-reflection effect and the use of right-angle prisms.

Abstract: A new development in angle measurement based on the internal-reflection effect (AMIRE) is described in which a pair of right-angle prisms is used to replace the previously used elongated critical-angle prisms, resulting in lower costs and a more compact size. Excellent linearity is achieved through careful alignment of the right-angle prisms. The measurement sensitivity and range can be selected through the use of light sources with different polarization states. Experiments with a prototype sensor demonstrated a measurement range of 1.6°, a resolution of 0.04 arcsec, and a nonlinearity error of ±0.1%. Both analytical and experimental results are presented.

Ray trace through a corner-cube retroreflector with complex reflection coefficients

Abstract: A vector formulation is used to derive an analytical expression for the complex reflectivity of a corner-cube retroreflector, with use of the complex reflection coefficients for the s and p polarization. This expression shows that the corner-cube retroreflector modifies the incoming electric field according to the angle of incidence and the ray path through the retroreflector. The change in the electric field depends on the errors in the surface finish, the coating nonuniformity, and the nonhomogeneity in the index of refraction in the case of the solid corner-cube retroreflector. The main point is that the corner-cube retroreflector conjugates the incident beam only in the case of a plane wave with a constant amplitude incident upon a perfect corner-cube retroreflector.

Complete method to determine transmission and reflection characteristics at a planar interface between arbitrarily oriented biaxial media

Abstract: The general case of monochromatic plane-wave reflection and refraction at oblique incidence from a planar biaxial–biaxial interface is presented for arbitrary principal-axes orientation in each region. A complete, systematic methodology is provided for calculating all properties of the transmitted and reflected light waves. The singularities that arise when one or both regions are taken to be isotropic are addressed, to our knowledge for the first time. Example calculations are presented for all cases. Finally, the methodology yields all wave parameters, including phase-velocity indices of refraction, angles of refraction and reflection, polarization angles, walk-off angles, and Poynting-vector relative magnitudes. Some common applications of this theory include multilayer structure analysis and the determination of internal angles for second-harmonic generation.

Coupled-wave analysis of lamellar metal transmission gratings for the visible and the infrared

Abstract: We theoretically and experimentally investigate the response, in the visible and in the near infrared, of micrometer- and submicrometer-period lamellar metal transmission gratings in vacuum and on silica and GaAs substrates. We use a coupled-wave analysis to characterize the grating response as a function of wavelength, period, grating profile, and dielectric constant of the metal and the substrate. Losses to the metal, which have been neglected in prior studies, are shown to be as large as 80% of the incident optical power. Absorption in the metal and the substrate, associated with complex refractive indices, leads to a broadening and a reduction in amplitude of Rayleigh wavelength resonance features in the transmission efficiency and reduces the extinction between orthogonal polarizations in the wire-grid polarizer limit. The results of transmission and photocurrent studies performed on metal–semiconductor–metal photodiodes fabricated on GaAs or GaAs–AlGaAs heterostructure substrates demonstrate the rigorous nature of the coupled-wave analysis, indicate experimental limitations for the application of an infinite grating approximation to model finite-period structures, and provide evidence for the presence of surface electromagnetic waves in the forward-diffracted optical intensity distribution. Qualitative agreement is also obtained between coupled-wave analysis results and transmission data reported in the literature for gold gratings on silica.

Apparatus and methods for laser-induced superficial alteration of a substrate

Abstract: An apparatus and method for superficially ablating and/or photochemically altering a substrate, e.g., a biological tissue, having a first refractive index, e.g., to a desired configuration, including a laser energy source which provides laser energy to an energy coupling wave generator which generates laser energy waves from the laser energy, the generator having a surface adapted to contact and form an interface with the substrate and having a second refractive index higher than the first refractive index, wherein laser energy entering the wave generator impinges on the surface at an angle of incidence greater than or equal to a critical angle for total internal reflection when the surface is not contacting the substrate, and wherein the wave generator couples the laser energy waves, e.g., refracted or evanescent waves, into the substrate at the interface to superficially ablate the substrate when contacting the substrate.

Prism fingerprint sensor using a holographic optical element

Abstract: A fingerprint sensor having a holographic phase grating glued on one right angle surface of a prism is described where a light source oriented normally relative to the hypotenuse surface of the prism illuminates an interface of the grating and finger surface. Incident light rays are refracted and absorbed where ridges of the finger surface contact the grating surface, whereas light rays are totally internally reflected in areas between and pores in finger surface ridges not in contact the grating surface. The reflected light rays, diffracted by the holographic phase grating, propagate normally (⊥) back into the right angle prism where they are reflected normally (⊥) out the remaining right angle surface of the prism by a second total internal reflection at the internal hypotenuse surface of the prism. The reflected light rays emerging from the sensor contain high contrast, detailed images of the ridges and valleys of the finger surface including pores in the ridges, i.e., a high quality fingerprint image oriented in a plane normal to the optical axis. The holographic phase grating eliminates image distortion due dimensional compression, and there is no necessity for optically correcting astigmatism in the image before capture. Fingerprint images of a quality that allows resolution of pores on the finger surface ridges are reliably obtained making the invented fingerprint sensor ideally suited for providing input to fingerprint recording, recognition and verification systems.

Projection type display device

Abstract: PROBLEM TO BE SOLVED: To provide a projection type display device capable of enhancing the brightness of a projected picture when plural light sources are used in the device SOLUTION: A light source device 11 is mounted on this projection type display device This light source device 11 is provided with a prism 30 as a light synthesizing means and combines light beams from light sources 1a, 1b by making the light beam from the light source 1a to be made incident on the side 30a of one side forming the apex angle of the prism to be reflected on the side 30b of other side and by making it to be emitted from the bottom side 30c of the prism and, moreover, by making the light beam from the light source 1b to be made incident on the side 30b to be reflected on the side 30a of other side and by making it to be emitted from the bottom side 30c In this case, the prism 30 is made so that angles of incidence θ of the light beams with respect to perpendicular lines of respective sides 30a, 30b are set equal to or smaller than 20° and, moreover, the angle of incidence θ' of the light beam entering from the side 30a to the side 30b is set equal to or larger than the critical angle of about 418° due to the refractive index of the prism Thus, since the light beams of respective lamps 1a, 1b are totally reflected to be combined without loss, the brightness of the projected picture is enhanced COPYRIGHT: (C)2000,JPO

Modified critical angle method for measuring the refractive index of bio-optical materials and its application to bacteriorhodopsin

Abstract: The critical angle technique is modified for the accurate measurement of the refractive index of bio-optical materials. Based on the analysis of reflection from the boundary of the material as a function of incident angle and polarization direction, the critical illumination angle is obtained by numerical differentiation of the reflection curve. As an example, the dispersion curve of bacteriorhodopsin is given. The measurement error and the effect of the host bovine skin gelatin on the results are analyzed.

Multilayer-coated optics: guided-wave coupling and scattering by means of interface random roughness

Abstract: For plane-wave light incident upon multilayer optical components, we use first-order perturbation theory to calculate two effects of interface roughness: (1) angle-resolved scattering and (2) guided-mode coupling. The interface roughness, which is assumed to be a random variable having root-mean-square roughness much less than the incident wavelength, is the perturbation parameter. When guided-wave mode resonances are inherent in optical component design, we show that fractions of incident energy scattered directly and coupled into guided-wave modes are comparable. It follows that, in consideration of multilayer optics, energy coupled into guided-wave modes can be an equally important consideration, as this energy may then end up as an additional contribution to scattering and absorption.

Direct solution to the inverse scattering problem for surfaces from near-field intensities without phase retrieval.

Abstract: We demonstrate a solution to the problem pertaining to the reconstruction of the profile of an interface separating two media of different refractive index, using near-field scattered intensity measurements. This is achieved by integration of the intensities of the scattered near fields over several angles of incidence, hence producing an effective incoherent source on the surface.

Optical device for forming an image of an uneven surface

Abstract: An optical device for forming an image of an uneven surface, including a plane-parallel plate with a pair of parallel plane surfaces which is made of a transparent material having a refractive index larger than that of water and transparent to illuminating light. An uneven object (object having an uneven surface) is placed in close contact with one plane surface of the plane-parallel plate. A light source illuminates the uneven object through the plane-parallel plate. Among light rays scattered back into the plane-parallel plate by the uneven object and totally reflected at the other plane surface of the plane-parallel plate, only light that is totally reflected at an angle larger than the critical angle at the boundary between the plane-parallel plate and water is taken in by an image-forming device.

Interface instability induced by an electric field in fluids

Abstract: An interface between two immiscible, nonionic fluids becomes unstable if an electric field is applied and if the angle between the field and the interface normal is smaller than a critical angle. We do not assume the presence of ions on the interface in contrast to previous work. The characteristic wave number k∗ of the undulations is proportional to the square of the field and inversely proportional to the surface tension. We also show that a thin layer on a capacitor plate loses its stability more easily than an interface far from the plates. New effects can be expected in near-critical fluids, in which the surface tension is small and k∗ can be much larger than the inverse of the capillary length. Moreover, k∗ ultimately exceeds the inverse of the correlation length very close to the critical point, where the critical behavior and the domain structure are drastically altered by electric field.

The polarizing beam splitter guide at BENSC

Abstract: A polarizing beam-splitter guide, theoretically described earlier, was installed in the neutron guide hall at BENSC in the winter of 1993/94. It splits the incoming neutron beam with wavelengths beyond 2.5 A into two oppositely polarized beams. The active elements of the splitter system are Si CoFe supermirrors deposited on Si wafers, which show a good polarization capability between the critical angle of Si of 0.047° per A neutron wavelength and a cut-off angle of 0.21° per A, i.e. twice the critical angle of natural Ni. For single mirrors in the supermirror region an average reflection coefficient of 90% was achieved at a polarization of 96% for the reflected beam while the transmission coefficient amounted to 80% for a polarization of 97%. These values apply for a magnetizing field of 300 G and improve slightly for higher fields. Preliminary results for the whole guide show a polarization above 92% for neutrons with a wavelength of 3 A.

Light Propagation in Scanning Near-Field Optical Microscopy

Abstract: Light propagation in the aperture scanning near-field optical microscope (a-SNOM) is studied theoretically, using the multiple multipole method (MMP). It is found that the light in the probe decays faster than exponentially. An explanation for this observation is given by means of ‘mode matching’ of the cylindrical waveguide modes. The exponential dependence between the gap-width and the light radiated beyond the critical angle is verified for 3D. The 1/e decay length fits very well with the length obtained using Fresnel’s formula. For a coating of infinite thickness, the near-fields are compared with results from rigorous diffraction theory obtained by Bouwkamp. Under certain circumstances, guided modes couple with surface modes, enhancing the amount of power propagating on the surface of the probe. Therefore, light emitted by the aperture interferes with the light coming from the surface of the metal cladding. The cladding needs to have a minimum thickness to avoid this unfavourable effect.

A novel method for determining thin film density by energy-dispersive x-ray reflectivity

Abstract: A technique utilizing the reflection of x‐rays to determine material density at flat surfaces is described. The effects of sample misalignment limit the accuracy of x‐ray reflectivity as typically practiced. These effects may be properly accounted for by measuring the critical angle for reflection at many different x‐ray wavelengths simultaneously from which an extrapolation of the position of the critical angle at infinite wavelength may be made. This extrapolation has the effect of correcting for sample misalignment. Use of the technique is demonstrated for single‐crystal silicon surfaces and for silica spin‐on‐glass thin films.