Showing papers on "Total internal reflection published in 1968"

Excitation of nonradiative surface plasma waves in silver by the method of frustrated total reflection

Abstract: A new method of exciting nonradiative surface plasma waves (SPW) on smooth surfaces, causing also a new phenomena in total reflexion, is described. Since the phase velocity of the SPW at a metal-vacuum surface is smaller than the velocity of light in vacuum, these waves cannot be excited by light striking the surface, provided that this is perfectly smooth. However, if a prism is brought near to the metal vacuum-interface, the SPW can be excited optically by the evanescent wave present in total reflection. The excitation is seen as a strong decrease in reflection for the transverse magnetic light and for a special angle of incidence. The method allows of an accurate evaluation of the dispersion of these waves. The experimental results on a silver-vacuum surface are compared with the theory of metal optics and are found to agree within the errors of the optical constants.

Internal Reflection Spectroscopy

Abstract: Reflection of light is a surface phenomenon—it is strongly dependent on the nature of the surface and can therefore be used to study surfaces. If the surface is flat and smooth, the nature of the reflection is called specular, i.e., mirrorlike, and obeys the simple law that the angle of incidence equals the angle of reflection.

Electric Fields Produced by the Propagation of Plane Coherent Electromagnetic Radiation in a Stratified Medium

Abstract: Explicit formulas are derived for the mean-square electric fields induced by plane electromagnetic radiation in a two-phase, three-phase, and N-phase stratified medium. The first (incident) and last phases are semi-infinite in extent. Boundaries separating phases are plane and parallel. Phases are isotropic with arbitrary optical constants. Simple relationships follow for special cases such as at the critical angle for a two-phase system. Equations for reflectance, transmittance, and phase changes on reflectance and transmittance are given. Details are given concerning the energy absorption process, especially in the two- and three-layer cases. Equations for the N-layer case are in terms of characteristic matrices which can be readily programmed for a computer.

Reflection and Refraction of a Beam of Light at a Plane Interface

Abstract: The reflection and refraction of a beam of light is treated. Approximate solutions of Maxwell’s equations are used to describe the electromagnetic field of the beam being limited in the transverse direction. The point of departure is the classical paper by Schaefer and Pich. The laws of reflection and refraction are derived. Fresnel’s formulas and their corrections are presented for both polarizations. The case of total reflection is investigated for E polarization in greater detail. The electromagnetic fields and the time-average Poynting vectors are explicitly derived for both the optically dense and less-dense media. The flow of energy at total reflection is studied extensively. It is shown that, due to the flow of energy in the less-dense medium, the center of gravity of the reflected beam is displaced, as was suggested by v. Fragstein. This leads to a shift of the totally reflected beam with respect to a geometrically reflected beam, as was experimentally demonstrated by Goos and (Lindberg-) Haenchen. New expressions for this “Goos–Haenchen shift” are derived. These expressions reduce to the classical formulas deduced by Artmann, v. Fragstein, Wolter, and Maecker if the angle of incidence is only slightly larger than the critical angle of total reflection. In consistency with Renard’s viewpoint they, however, predict vanishing shifts in the limit of grazing incidence.

Element pattern nulls in phased arrays and their relation to guided waves

Abstract: In recent years, unusual dips or nulls have been observed in the element patterns of certain phased-array antennas at angles closer to broadside than that for which an endfire grating lobe exists. These nulls are known to bear a direct and simple relation to a total reflection condition which occurs when all elements of the array are excited. The purposes of this paper are to investigate the basic cause of these element pattern nulls, and to clarify the relationship between these nulls and possible guided waves which may be supported by the array face. It is shown herein that, for a certain class of arrays, these nulls (actually the total reflection condition) are caused by the forced resonance of a higher external mode in the vicinity of the array aperture. The nature of this resonance is demonstrated on a simple infinite array representative of a class of structures which permit external resonances. A detailed analysis of this array (of waveguide-fed slots covered by a dielectric layer) yields a simple equivalent network from which the existence, approximate angular location, and qualitative behavior of the element pattern null are determined by inspection. There are two types of guided waves which are of concern here, surface waves and leaky waves. It is shown that the actual array cannot support a true surface wave, and that the surface wave customarily associated with element pattern nulls is really a driven surface-wave-like field which appears on the array face only at precisely the total reflection condition, and which is indistinguishable in its properties from a true surface wave on a modified (corrugated) structure, not on the actual array. The leaky wave, whose role is explained here for the first time, is a true mode of the actual array and radiates at an angle close to that for the element pattern null. Its influence on the element pattern null is akin to the relation between free and forced resonances, and its attenuation constant yields the width of this null.

Achromatic Wave Plates for the Visible Spectrum

Abstract: We report the experimental demonstration of an optical quarter-wave plate having a retardation of 90°±1° in the region from 4000 to 8000 A. The device is based on the synthesis procedure of Harris, Ammann, and Chang and consists of six sapphire wave plates with appropriately oriented principal axes. The device does not suffer from thermal or angular problems as do longer, narrow-band birefringent networks. Results comparing a 10-plate unit with the above 6-plate unit are given.

Optical Measurements on Liquid Metals Using a New Ellipsometer

Abstract: A new kind of ellipsometer which employs continuously rotating sheet polarizers is described. It enables the restored azimuth Ψ and the differential phase change Δ for light reflected from a metal surface to be obtained very directly from null settings of a polarizer or analyzer with a precision of 0.1°. The instrument has been used to study the optical constants of liquid metals, especially mercury, in the wavelength range 0.4–0.7 μ. Particular attention was paid to the problem of surface contamination, and evidence is presented that a glow discharge is particularly effective in removing this. Measurements have been carried out on surfaces in contact with glass and quartz as well as upon free surfaces. The results are internally consistent but differ significantly from the predictions of the Drude free-electron theory.

Brillouin Scattering in Birefringent Media

Abstract: The theory of Brillouin scattering is extended to incorporate birefringence. The necessary modifications to the Bragg laws are derived by the methods of physical optics. An integral equation method is used to calculate intensities of the first-order lines scattered by longitudinal and transverse acoustic waves in an infinite slab of birefringent crystal. This calculation also differs from those of previous authors in taking full account of internal reflection. Depletion of the incident beam is accounted for. No restriction is made to acoustic propagation parallel to the crystal faces. The intensity formulas for various cases of acoustic mode and incident optical polarization are found to differ in geometrical structure, and the differences can alter the intensities substantially.

Wave Behavior at an Interface of a Semi‐Infinite Moving Anisotropic Medium

Abstract: The wave behavior at an interface between an isotropic medium and a moving anisotropic medium for an arbitrary plane of incidence is studied. Modified forms of Snell's law for refraction are obtained for both the ordinary and the extraordinary waves when the moving medium is uniaxially anisotropic. The critical angle for total reflection is computed for the extraordinary wave as a function of medium velocity and anisotropy. It is found that the reflected and refracted waves behave quite differently, depending on whether the moving medium is a uniaxial crystal or a magneto‐ionic plasma in an infinitely strong magnetic field. Conditions for the existence of the Brewster angle, even for a prependicularly polarized wave incident normal to the direction of medium motion, are examined. Curves for reflection coefficient are plotted vs medium velocity.

Simultaneous and Independent Determination of the Refractive Index and the Thickness of Thin Films by Ellipsometry

Abstract: In ellipsometry, the interesting case of light incident from a dense medium such as an inert liquid onto a film over an absorbing substrate has been considered theoretically for the two cases (i) when the angle of incidence ϕ0 is less than the critical angle ϕc and (ii) when ϕ0 > ϕc. Detailed calculations indicate that the sensitivity with which the thickness of the film can be measured is nearly the same, whatever the first medium, for case (i) but that in case (ii) the sensitivity is very poor. Further, by combining the measurements of the ellipticity parameters with first air and then a liquid as the immersion medium, it is possible to evaluate independently by a self-consistency procedure both the thickness and the refractive index of the film. Measurements of oxide films on a substrate of silicon indicate that the refractive index is 1.484±0.004 in the thickness range 80–300 A for λ 5461 A and not 1.460 as has been assumed by previous workers.

Reflection of Finite‐Amplitude Ultrasonic Waves. I. Phase Shift

Abstract: When an ultrasonic wave is reflected from an interface, a phase shift that is dependent on the angle of incidence may occur. If the wave is nonsinusoidal, this phase shift causes relative spatial shifting of the Fourier harmonic components. The assumption of independent reflection of the Fourier harmonics allows the use of linear theory to calculate the change in the phase angle between the fundamental and the second‐harmonic components in the distorted wave. A pulse technique is used to measure this change in phase angle. Agreement between theory and experiment is good for the phase shift upon reflection from water‐copper, from water‐duralumin, and from water‐mica‐glycerin interfaces when correction is made for finite‐amplitude effects between the interface and the receiving transducer.

Surface-wave effects on dielectric sheathed phased arrays of rectangular waveguides

Abstract: A further study of the effects of dielectric slabs on the radiation characteristics of an infinite array of rectangular waveguides has been carried out. It is found that, in addition to causing substantial and sometimes beneficial changes in the array performance, the presence of dielectric slabs can give rise to sharp resonant peaks in the reflection coefficient at certain scan angles. The occurrence of such resonant peaks at which total reflection occurs is contingent upon the presence of space harmonics which have surface-wavelike field distribution. Extensive data for both the H and E planes of scan, when the array is covered with a single slab, have been obtained and are presented here. This paper discusses the influence of the dielectric constant, slab thickness, and waveguide wall thickness on the resonant peak location, and points out the relationship between the resonance phenomenon and the surface wave propagation over a corrugated surface. It also presents some further results for the thin sheath and their extension to multiple sheaths.

Improvements in photomultipliers with total internal reflection sensitivity enhancement.

Abstract: An improved geometry for coupling a beam into a photomultiplier with total internal reflection sensitivity enhancement is described which allows this technique to be used with large sized beams. The equations giving the increase of the photocathode’s absorption efficiency by the use of internal reflection within the window are discussed and conditions for best performance specified. The calculations, based on modifications of experimentally verified equations employed in internal reflection spectroscopy, predict that cathodes only a few monolayers thick could be made to absorb almost all the light falling on them in very few reflections. It then is shown that this will result in high quantum efficiencies with a much reduced spectral dependence. Particularly high increases may be expected for the less efficient cathodes such as S–1. The procedure is shown to relax the requirements on electron escape depth and absorption coefficient of the cathode material so much that the range of possible materials is considerably enlarged. Also, surface and defect level photoemitters will become practical. This and the change of work function with material thickness raise the possibility of extending the region of operation of photomultipliers more into the ir. Photomultipliers so built could also show a higher frequency response to modulated light beams. Finally, means of reducing the dark current and obtaining the multiplex gain in these photomultipliers are discussed.

Improved resolution and signal‐to‐noise ratios in total internal reflection holograms

Abstract: This Letter reports improvements in resolution and signal‐to‐noise ratio for total internal reflection hologram reconstructions. It outlines the conditions employed to produce these results and indicates some of the relevant properties.

Reflection and Transmission of Electromagnetic Waves by a Moving Dielectric Slab. II. Parallel Polarization

Abstract: The reflection and transmission of a plane wave, with its electric vector polarized in the plane of incidence, by a moving dielectric slab are investigated theoretically. Two cases of the movement are considered: (a) the dielectric slab moves parallel to the interface, (b) the dielectric slab moves perpendicular to the interface. It is shown that, in general, the reflection and transmission coefficients for an incident plane wave with its electric vector polarized in the plane of incidence are different from those for an incident plane wave with its electric vector polarized normal to the plane of incidence, except for case (b) for normally incident waves. Detailed results on the reflection and transmission coefficients for case (a) for normally incident waves are given and discussed.

Internal Reflection Spectroscopy I: Effect of Angle of Incidence Change:

Abstract: One of the variables in internal reflection spectroscopy is the angle of incidence on the reflecting surface. Varying the angle may (1) improve spectral quality, (2) change the beam penetration within the sample, and (3) change the number of reflections, thus changing total absorbance.

Light deflection system

Abstract: A display system using a fluid stream as an optical fiber carrying a light beam, by total internal reflection, to a display panel. The fluid stream is selectively directed to a transparent character on the display panel, and the light beam is released from the fluid stream by inducing a sharp bend into the fluid stream.

Far-field patterns of electron-beam pumped semiconductor lasers

Abstract: Laser action is described for total internal reflection modes such that the far-field pattern is a circular ring surrounding the crystal in a plane perpendicular to the rectangular cavity faces. A number of recent experiments have shown that this far-field pattern can be observed in GaAs samples as well as in ZnO and CdS. Experiments are reported for single crystals at a temperature of 77°K pumped by a low-voltage electron beam using 100-ns low-duty cycle pulses. Photographs of the far-field pattern show a narrow line extending 360° around the axis of the crystal and having an angular width of 5 to 10°. Photographs of the near-field pattern indicate that the laser light is emitted in quadrants at the four corners of the rectangular cavity, combining at large distances to produce a 360° pattern. Experimental results on a number of CdS crystals of various thicknesses show that the voltage threshold for lasing (at constant current density) for the total internal reflection mode varies approximately as the 0.7 power of the crystal thickness. Losses from total internal reflection are negligible, and for CdS and ZnO platelets absorption losses are also so small that lasing can occur when the penetration depth of the electrons is only 1/40 of the total crystal thickness. Because of these low losses, lasing has been observed in ZnO and CdS at 2.5 keV and a current density of about 5 A/cm2for crystal platelets approximatley 2 microns thick. Since the penetration of a 2.5 keV electron is only about 500 A, this indicates that surface losses in CdS and ZnO with as-grown surfaces are also small. A similar thickness dependence is reported for GaAs doped with 1.5 \times 10^{19} Zn atoms/cm3, but absorption losses appear to be higher. Thus a 2-micron-thick crystal of GaAs pumped with an electron beam of the same current density as above lases with a voltage threshold of 10 keV. The threshold voltages measured for ZnO, CdS, and GaAs are considerably lower than any previously reported for electron-beam pumped semiconductor lasers.

Mechanism of formation of the interlamella dislocation network in polyethylene single crystals

Abstract: It was found experimentally that bilayered polyethylene single crystals with an orientational misfit angle larger than the critical angle, θ*, show moire pattern and only those with an angle smaller than θ* show the interlamella dislocation network. The intermediate pattern, which could neither be classified into the typical moire pattern nor the typical interlamella dislocation network, was found in the vicinity of θ*. Criteria for discrimination between the moire pattern and the interlamella dislocation network are discussed. The crystal with a misfit angle a little larger than θ* also comes to show the feature of the dislocation network during long storage of the crystal in the mother solution at the crystallization temperature. θ* is, therefore, a function of the time of storage. A mechanism is presented such that crystal lattices near the interfacial boundary are distorted to form the dislocation network by intermolecular force between the overlying crystals when the misfit angle is smaller ...

Detection of toxic organophosphoru airborne substances by frustrated multiple internal reflection spectroscopy

Abstract: A thin germanium crystal prism in the form of an isosceles trapezoid or parallelogram whose base surface and opposite parallel surface are coated with platinum about 70 millimicrons thick, the coating having been applied in a vacuum on the order of 10 millimicrons for effective adsorptiveness. Sampled atmosphere is flowed across the base and the opposed surface of the crystal while infrared of wavelength band 9-10 microns is directed through the crystal for multiple internal reflection and the amplitude of infrared that passes through the crystal is monitored.

The Effect of Optical Polarization on Reflection Spectra

Abstract: The theoretical basis for polarization effects in reflection spectra are reviewed. It is shown that light polarized parallel to the plane of incidence interacts more strongly with the absorbing species than does light of perpendicular polarization except under conditions of internal reflection when the absorber is a thin film between two nonabsorbing media. In this instance the relative degree of interaction is determined by the refractive indices of the three phases. Experimental results are presented which show the predicted effects for internal reflection spectroscopy both when the absorbing medium is a solution of (CH3)4NCl in D2O and when it is a monolayer of stearic acid.

Highly efficient raman emission device

Abstract: The invention includes an elongated Raman active medium having total internal reflection means along its longitudinal dimension. Optical pumping is by pulses of duration of the order of several picoseconds or less made incident upon one end of the medium and direction along the longitudinal axis thereof. The Raman emission inherently traverses a zigzag path within the medium at an angle such that the group velocity of the Raman and pump pulses is matched, i.e., differences in group velocity of the pump and Raman radiation due to the dispersion of the medium are compensated for.

Reflection and transmission of a plane electromagnetic wave at a fast moving boundary

Abstract: An interesting phenomenon of a plane electromagnetic wave at a fast moving boundary is discussed. When the boundary moves at the speed of light, the field intensity of the reflected wave is equal to that of the incident wave. Such a case may possibly occur in the ionizing process of atmospheric gases by the light of the sun.

Face-pumped laser device with optical path folding

Abstract: A face-pumped laser device employs a prism with an index of refraction at least equal to the square root of two adjacent and optically contacted to the surface of the active laser medium. The prism provides for refraction and total internal reflection of the pumping radiation which is directed to and is substantially uniformly incident upon the surface of the active laser medium, thus increasing the pumping flux density by the square root of two over conventional techniques. A plurality of prisms positioned on the opposite side of the laser medium are utilized in conjunction with the first mentioned prism to fold the optical path in such a manner that a generated or input laser beam may be made to penetrate a different region of the laser medium on each pass.