Showing papers on "Total internal reflection published in 1988"

Electromagnetic wave propagation through a dielectric–chiral interface and through a chiral slab

Abstract: The reflection from and transmission through a semi-infinite chiral medium are analyzed by obtaining the Fresnel equations in terms of parallel- and perpendicular-polarized modes, and a comparison is made with results reported previously. The chiral medium is described electromagnetically by the constitutive relations D = ∊E + iγB and H = iγE + (1/μ)B. The constants ∊, μ, and γ are real and have values that are fixed by the size, the shape, and the spatial distribution of the elements that collectively compose the medium. The conditions are obtained for the total internal reflection of the incident wave from the interface and for the existence of the Brewster angle. The effects of the chirality on the polarization and the intensity of the reflected wave from the chiral half-space are discussed and illustrated by using the Stokes parameters. The propagation of electromagnetic waves through an infinite slab of chiral medium is formulated for oblique incidence and solved analytically for the case of normal incidence.

Why some things are darker when wet

Abstract: Angstrom has proposed that rough absorbing materials are darker when wet because their diffuse reflection makes possible total internal reflection in the water film covering them, increasing the likelihood of the absorption of light by the surface His model is extended here in two ways: the probability of internal reflection is calculated more accurately, and the effect on absorption of the decrease of the relative refractive index (liquid to material instead of air to material) is estimated Both extensions decrease the albedo of the wetted surface, bringing the model into good agreement with experiment

High precision optical surface sensor.

Abstract: A noncontact optical surface sensor with <1-nm resolution has been developed. The principle of this high precision optical surface sensor (HIPOSS) is based on the focus detection technique which has been employed in the pickup for optical disks. For focus detection, we chose the critical angle method of total reflection which used the steep reflectivity change around the critical angle. The HIPOSS was designed to increase the sensitivity and to eliminate some errors for nanometer order profilometer use. The size of the HIPOSS optical head is as small as 45 × 30 × 65 mm, so it can be installed side by side with a diamond stylus in the profile measuring instrument. These styli, if we term the HIPOSS an optical stylus, can be interchanged easily to obtain profile data on the same surface by different means, contact and noncontact. The repeatability of going and returning measurements is <1-nm rms, and the difference between HIPOSS and stylus measurements is also below 1-nm rms for most example surfaces. Using the high speed response of the HIPOSS, 3-D profile measurement over the workpiece and in-process measurements for ultraprecise diamond turning are also demonstrated.

Nonlinear selective reflection from an atomic vapor at arbitrary incidence angle

Abstract: We calculate the reflection coefficient for a light beam incident on the interface between a dielectric and a resonant atomic vapor to first order in the dipole polarization in the vapor. The angle of incidence and the polarization direction are chosen arbitrarily, and saturation is fully accounted for. The atoms are supposed to get deexcited at collisions with the surface. The resulting transient behavior of atoms leaving the surface is responsible for a nonlocal response. This spatial dispersion near the surface is known to produce a natural-linewidth-limited resonance in the vapor reflection coefficient at normal incidence. Our analysis shows that this sub-Doppler structure is broadened by the residual Doppler effect for non-normal incidence. This structure disappears at the critical angle for total internal reflection, where one predicts a conventional Voigt-type dispersion response, based on the complex-refractive-index approach. We also calculate the saturation broadening of the atomic response for large intensities. Beyond the critical angle, the spectral response suddenly shifts from dispersion to absorption line shapes. In the case of total internal reflection, the spatial dispersion leads to an additional Lorentzian broadening, which results from an effective imaginary Doppler shift at passage through the evanescent wave (transit-time broadening).

Fiber optic which is an inherent chemical sensor

Abstract: A fiber optic element is used to detect the presence of chemical or biological species by measuring changes in the total internal reflection characteristics of the element produced by changes in the index of refraction of a clad or layer (12) of a material which reacts with the chemical or biological species.

Multiple-fiber optical component and method for manufacturing of the same

Abstract: Opposed ones of optical fibers respectively secured in a plurality of guide grooves formed in first and second blocks, are jointed to each other through an optical film formed on at least one of their opposed inclined end faces in such a way that their optical axes are aligned with each other. Further, each of optical fibers similarly disposed on a third block is formed at its one end face with a total reflection film and is arranged in parallel to the optical fibers of the first and second blocks in such a way that an optical signal incident to the respective fibers of the first block is propagated through the splitting films and total reflection films along optical axes of the associated optical fibers of the third block.

Evanescent wave infrared spectroscopy of liquids using silver halide optical fibers

Abstract: Infrared spectroscopic measurements of liquids were performed in an attenuated total internal reflection cell, using infrared transparent silver halide fibers. As an example, we studied evanescent wave absorption in water. In particular, we analyzed absorption dependence on various physical parameters, such as the length of the absorbing medium and the geometry of the beam at the fiber entrance and exit faces. Absorption peaks were easily traced and experimental results correlated well with theoretical calculations. These studies may lead to practical uses of fiberoptic‐based evanescent wave spectroscopy.

Infrared spectroscopy of thin silicon dioxide on silicon

Abstract: An infrared technique has been devised to study the structure of very thin films on substrates of high refractive index. Optical spectrum amplification of three orders of magnitude is theoretically available. A series of refractive index enhanced multiple internal reflection spectra reveals a clear thickness‐dependent structural transformation in thermal SiO2. The spectra suggest a shift in ring statistics, from smaller to larger, with increasing distance from the oxide‐silicon interface.

Investigation of optical tunneling through nonlinear films

Abstract: The tunneling phenomenon of light waves that are totally reflected at one of the film interfaces will be considerably modified when the dielectric coefficient of the film becomes intensity dependent. We present an exact analytical approach that describes the tunneling of totally reflected, transverse-electric-polarized plane waves through a nonlinear film, the dielectric function of which may reveal material saturation. Within certain parameter ranges the configuration shows a pronounced switching between total internal reflection (off state) and the onset of complete transmission (on state). The switching characteristic can be tuned either by the angle of incidence or by the input intensity from monostable to bistable response. An experimental demonstration of the predicted results has been performed by using a liquid-crystal p-methoxybenzilidene-p-n-butylaniline film sandwiched between two optical prisms.

Inter-sub-band absorption in GaAs/AlGaAs single quantum wells

Abstract: The observation of resonant inter-sub-band absorption in AlxGa1-xAs/GaAs single quantum wells using a total internal reflection geometry is reported. It is shown that strong absorption is obtained provided that a large optical electrical field perpendicular to the quantum wells is generated. Such conditions occur when the well is close to the reflecting boundary and reflection occurs at a semiconductor/metal interface, but not when reflection occurs at a semiconductor/vacuum interface. The optical properties of the whole structure can be quantitatively described by considering the system as a multi-layer dielectric stack.

Optical liquid level sensor using a polytetrafluoroethylene perfluoroalkoxy material

Abstract: An optical liquid level sensor has an optically-transmissive body (28) provided with a frusto-conical tip end portion (32). When the tip end portion is exposed to air, the angle of incidence (θ i ) of light at each of three points of reflection (b,c,d) is less than the critical angle (θ c ) such that substantially all light transmitted through the body will be reflected internally. However, when the tip end portion is exposed to a liquid, light is refracted, and the intensity of the reflected light is reduced. The intensity of the reflected light is used to indicate whether the sensor is above or below the surface of the liquid.

Mapping cell-glass contacts of Dictyostelium amoebae by total internal reflection aqueous fluorescence overcomes a basic ambiguity of interference reflection microscopy.

Abstract: The widespread ability of eukaryotic cells to produce thin cytoplasmic sheets or lamellae 100–200 nm thick can give rise to uncertainties in the interpretation of interference reflection microscopy (IRM) images when cell-substratum topography is the key interest. If allowed to spread upon a poly-L-lysine-coated surface, Dictyostelium discoideum amoebae typically form ultrathin lamellae of approximately equal to 100 nm thickness by cytoplasmic retraction. Whereas the cell body is grey, the lamellae appear very dark under IRM optics. These dark areas could be misinterpreted as stemming from a closer cell-substratum apposition beneath the lamellae than the cell body. This ambiguity can be avoided if the technique of total internal reflection aqueous fluorescence (TIRAF) is used in conjunction with a high refractive index glass (n = 1.83) as substratum. Contributions to the image generated by thin cytoplasm and also variable cytoplasmic refractive index are thereby minimized due to the extremely short range of the ‘illuminating’ evanescent wave. From our comparative IRM and TIRAF study of the ultrathin lamellae of Dictyostelium amoebae it is concluded that the cell-glass gap is relatively uniform beneath the entire cell. We briefly discuss the sensitivity of several cell types to TIRAF, the generation of ultrathin lamellae and the nature of the cell-glass gap.

Ferromagnetism in ultrathin metastable films of fcc Fe, Co, and Ni (invited)

Abstract: We have applied spin‐polarized neutron reflection at a grazing angle of incidence to study the ferromagnetic behavior of thin magnetic films down to the monolayer thickness level. The reflected intensities I+ and I− for spin parallel (+) or antiparallel (−) to the sample magnetization are measured near the angle θc for total reflection: deviation of the flipping ratio F=I+/I− from unity occurs only for ferromagnetic ordering. In general, deviations of F from unity are so small that an accurate determination of the magnetic moment per atom μ is not possible. The success of the present experiments relies on the enhancement (∼500×) of the magnetic signal when the film is overcoated with a nonmagnetic layer of thickness sufficient to produce constructive interference in the reflected neutron wave field. With this method, we have determined the magnetic moments in films of the metastable fcc phases of Fe and Co, grown epitaxially on Cu(001) single‐crystal substrates. The fcc Fe(001) films have lowered Curie te...

Observations of internal beam production in barium titanate phase conjugators

Abstract: We have observed a variety of internal beam configurations in photorefractive BaTiO3 pumped by a cw Ar+ laser at 514.5 nm. Among these configurations was a total-internal-reflection ring resonator contained entirely within the crystal, with light circulating unidirectionally in the plane of the beam fanning. Phase-conjugate responses were in general found to depend critically on system parameters, in particular, on the separation between the pump focusing lens and the crystal. During the pulsation mode of the phase-conjugate reflection, a sudden frequency shift of 5–10 Hz was observed to occur during the pulse’s trailing edge. Certain internal beam patterns were found to be frozen into the crystal and were nearly invariant to small lateral motions of the pump beam across the crystal. Phase-conjugate returns, which would appear to the naked eye to be cw, were often found to possess nearly periodic fluctuations in amplitude and in center frequency.

Polarization properties of a cube-corner reflector

Abstract: The polarization properties of a solid cube-corner reflector, using total internal reflection, are analysed using some general properties of the Jones matrices. This description leads to the conclusion that all non-absorbing systems, including the cube-corner, may be considered as a single linear retarder with suitable relative rotation between input and output reference axes. Simple analytical results are obtained for the case of normal incidence, and, in particular, it is shown that a cube-corner of refractive index 1·76476 functions as a 90° retarder. Results of numerical calculations for non-normal incidence are summarized. The analysis presented contrasts with the determination of elliptically polarized eigenstates, as given by Peck, and has proved particularly useful when incorporating cube-corner reflectors in interferometers.

Analysis of reflection-type optical switches with intersecting waveguides

Abstract: The reflection phenomenon of the guided mode in optical switches with intersecting single-mode waveguides is investigated by the wave approach. The guided mode is expanded into an infinite spectrum of plane waves and the condition of total internal reflection is applied. The power reflectivity of the guided mode is calculated and is used to estimate the extinction ratios. It is found that at refractive index variation of about 1 percent, large extinction ratios (>30 dB) are achievable if the refractive index difference between the waveguide core and cladding is smaller than the voltage induced refractive index variation by about one order of magnitude. The intersecting angle is found to be limited to about the critical angle and is required to be large enough to prevent degradation of the extinction ratios and to keep scattering losses small. It is also indicated that by displacing the electrode, to account for the Goos Haenschen shift, it is possible to further reduce the scattering losses. >

Displacement of the intensity peak in narrow beams reflected at a dielectric interface

Abstract: The net displacement of the intensity peak in relatively narrow Gaussian beams reflected at a dielectric interface is shown to be produced by a combination of four distinct nonspecular effects, namely, lateral, focal, and angular shifts and a modification of the beam-waist magnitude. We also find that these effects cause the axis of the reflected beam to follow a trajectory that depends on the beam width and on the distance from the waist of the geometric-optical reflected beams. To determine all the details of this nonspecular behavior, we derive a new expression for the reflected field; in contrast to previously reported results, this expression also holds for small beam widths and for incidence angles equal or close to the critical angle of total reflection. Our derivation yields accurate results for the four distinct nonspecular effects and provides a consistent explanation of the available experimental data on the net displacement of the beam peak.

Fibre optic sensor for liquid level and other parameters

Abstract: A fibre optic sensor, particularly for ascertaining fluid levels, utilizes at least two optical fibres having at least a portion thereof embedded in a transparent substrate material of similar refractive index. One of the fibres is coupled to a light source, the other to a light detector. The fibres are oriented in a plane relative to the interface between substrate and fluid so that light exiting the source fibre is coupled to the detector fibre when total internal reflection at the interface occurs in the presence of a first fluid. In the presence of a second fluid of higher refractive index than the first fluid there will be no coupling. Several different embodiments, to achieve discrete or continuous level sensing or the sensing of other parameters are disclosed.

Lighting device for a liquid crystal display device

Abstract: A device for back-lighting a liquid crystal display device has a lamp having a light emitting straight portion and a reflector plate. The reflector plate has a central portion provided under the light emitting straight portion and a pair of inclined side portions adjacent both sides of the central portion, the central portion having a total reflection surface, and each the side portion having a diffuse reflection surface.

Fibre optic sensor for the continuous measurement liquids level and other parameters

Abstract: A fibre optic sensor, particularly for ascertaining fluid levels, utilizes at least two optical fibres having at least a portion thereof embedded in a transparent substrate material of similar refractive index. One of the fibres is coupled to a light source, the other to a light detector. The source fibre illuminates the interior of the substrate so that light exiting the source fibre is coupled to the detector fibre when total internal reflection at the substrate/fluid interface occurs in the presence of a first fluid. In the presence of a second fluid of higher refractive index than the first fluid, there will be no coupling, due to the loss of light into the fluid by refraction. The mechanism for coupling light into the detector fibre is fluorescence within that fibre causing it to provide a light signal which varies with the level of the second fluid. Several different embodiments, to achieve continuous level sensing or the sensing of other parameters, are disclosed. As well, the issue of lead fibre insensitivity to changes in optical attenuation is addressed through a novel scheme which requires two light sources and two light detectors and utilizes the self attenuation of the fluorescent optical fibre to achieve a ratiometric measurement.

Lens design for acoustic microscopy

Abstract: Design criteria for acoustic microscope lenses are examined with respect to their intended application. Aside from buffer rod material and F-number, the factors influencing the lens design are the critical angle for surface wave excitation, lens illumination, and leak rate of the surface wave on the sample. It is found that the design criteria are different for surface and subsurface examination and that for different applications and materials, different lenses are required for optimum imaging performance. A formalism for evaluating the performance of an acoustic microscope by considering its response in the time domain, both theoretically and experimentally, is presented. >

Reflection and transmission of self-focused channels at nonlinear dielectric interfaces.

Abstract: We show with an extensive numerical study that the global reflection and transmission properties of a finite-width optical self-focused channel incident at an oblique angle to an interface separating two self-focusing nonlinear media can be categorized into three distinct regimes of behavior as the incidence angle is varied through the angle for total internal reflection. The largest regime in parameter space is the nonlinear regime, where a channel undergoes either total internal reflection or transmission, in marked contrast to the well-known linear Snell’s law behavior. The beam asymptotics in this latter region are quantitatively explained by a recent equivalent-particle theory.

Finger imaging apparatus

Abstract: A curved cylindrical segment platen (18) has a concave touching surface (18b). An interrogating slit light beam is scanned around the platen to scan a finger held against the touching surface. An optical imaging system images (20) the zone illuminated onto an array of photo-transducers (22) to provide a signal representing the fingerprint. The optical system is rotated (40) around the platen. The axis (17) of the interrogating light beam (16) is substantially normal to the touching surface (18b). The axis (28a) of the imaging system is off normal by about 56 degrees, an amount which is greater than a critical angle equal to the maximum angle of refraction (MAR) in the platen. This critical angle is approximately 41 degrees. The axis (28) of the imaging system is also off normal to the non-touching surface (18a) by an angle that is less than this critical angle of 4l degrees and thus less than the angle of total internal reflection (TIR). As a consequence, the image at the photo-transducers provides a completely dark valley zone and a sharply contrasting light image ridge ,zone.

Total reflection prisms as achromatic IR retarders

Abstract: Retarders based on total internal reflections are discussed. Quarterwave retardation can be obtained by a single reflection when one is using material of high refractive index (≥2.4), as it is available for the IR range. Alternatively, the influence of the beam divergence can he efficiently compensated for. Several optical designs and first results are presented.

Optical waveguide element, method of making the same and optical coupler employing optical waveguide element

Abstract: An optical waveguide element includes an optical waveguide formed on a light-transmissive dielectric substrate and having a higher refractive index than the refraction index of the substrate, the optical waveguide including a region having an effective refractive index which varies nonlinearly in a direction in which a light wave is propagated through the optical waveguide. The light wave guided through the optical waveguide enters the region, in which the angles of incidence and reflection of the guided wave at the boundary between the region and the substrate is gradually reduced due to the variation in the effective refractive index. When the angles of incidence and reflection of the guided wave becomes smaller than a critical angle, the guided wave is emitted out of the waveguide. Since the effective refractive index changes nonlinearly with respect to the distance the guided wave is propagated, the light emitted into the substrate tends to converge at a point, and the beam pattern of the emitted light is spread less.

Application of a grazing-incidence X-ray diffraction technique to the depth-resolved analysis of structural transformations due to surface treatments

Abstract: An experimental set up for X-ray diffraction experiments at grazing incidence is described. Adjustment and calibration procedures are defined. It allows identification of phases at increasing depth in thin films, with a resolution of 50 nm, by varying the incidence angle above the critical angle of specular reflection. Some examples are given to illustrate the potential of the technique in studies of the effects of surface treatments on bulk specimens. The examples are implantation films with thicknesses between 50 and 500 nm, and also rough films resulting from friction tests of these implanted surfaces.

Optical response of nonlinear absorbing and saturable superlattices

Abstract: We investigate the obliquely incident transmittance and reflectivity of a superlattice consisting of N unit cells. Each unit cell is formed of two absorbing nonlinear films. The absorption coefficient, as well as the refractive index, is assumed to depend on the light intensity. Additionally, the saturation of the nonlinearity is taken into account. We use a numerical approach, which we show to be consistent with a recently published analytical model [ A. A. Maradudin , in Optical and Acoustic Waves in Solids—Modern Topics, BorissovM., ed. ( World Scientific, Singapore, 1983)] in the limit of vanishing absorption and saturation. In detail, we investigate the optical response of a superlattice, illuminated by a plane wave close to the edge of the stop gap, as it relates to the input flux. We show that the combined effects of linear–nonlinear absorption and saturation will considerably affect bistable switching from the low-transmission to the high-transmission state. Eventually just this switching can disappear.

Angular sensitivity of a vacuum photodiode, or does a photodetector always count absorbed photons?

Abstract: The response of a vacuum photoemissive photodiode to a light beam has been investigated as a function of the angle of incidence in order to check whether the response is always proportional to the absorbed number of photons. By working mainly in the region of total internal reflection and measuring the reflected beam with an auxiliary detector at near-normal incidence, we were able to determine the absorptivity and to compare it with the measured photoelectric current. We found that the ratio of the two quantities is constant and independent of the angle of incidence for TE waves but not for TM waves. The results suggest that there exists an extra loss mechanism for TM waves, which may be connected with plasmon generation. Because of this extra loss, the response of the detector to TM waves is not a direct measure of the number of absorbed photons.

Transmission type screen

Abstract: PURPOSE:To prevent an incident light from becoming a stray light in a screen, while becoming a double image and being emitted in the forward direction, and to improve the contrast by scattering or absorbing the incident light which cannot be utilized as a total reflection light by a prism surface CONSTITUTION:A transmission type screen is provided with a structure on which a black absorbent is applied to a part of a prism surface in order to absorb an incident light which cannot be deflected in a normal direction, or the surface is roughened by flawing a part of said surface in order to diffuse said light For instance, when an incident angle in the center of a screen 5 of an incident light 3 which cannot be deflected in the normal direction is 60 deg, and when the incident angle is 50 deg, the black absorbent 2 is applied to the prism surface 1 of a part of about 1/6 of the upper part of the screen 5, and a part of about 1/2 of the upper part of the screen, respectively, by which a double image is obviated In this regard, in addition to a method for applying the black absorbent, it is also available that an unnecessary incident light is scattered by roughening the prism surface