Showing papers on "Reflection (physics) published in 1976"

Nonlinear phenomena in the ionosphere

Abstract: 1. Introduction.- 1.1 Data on the Structure of the Ionosphere.- 1.2 Features of Nonlinear Phenomena in the Ionosphere.- 1.2.1. Nonlinearity Mechanisms.- 1.2.2. Qualitative Character of Nonlinear Phenomena.- 1.2.3. Brief Historical Review.- 2. Plasma Kinetics in an Alternating Electric Field.- 2.1. Homogeneous Alternating Field in a Plasma (Elementary Theory).- 2.1.1.Electron Current-Electronic Conductivity and Dielectric Constant.- 2.1.2.Electron Temperature.- 2.1.3.Ion Current-Heating of Electrons and Ions.- 2.2. The Kinetic Equation.- 2.2.1. Simplification of the Kinetic Equation for Electrons.- 2.2.2. Transformation of the Electron Collision Integral.- 2.2.3. Inelastic Collisions.- 2.3. Electron Distribution Function.- 2.3.1. Strongly Ionized Plasma.- 2.3.2. Weakly Ionized Plasma.- 2.3.3. Arbitrary Degree of lonization-Concerning the Elementary Theory.- 2.4. Ion Distribution Function.- 2.4.1. Simplification of the Kinetic Equation.- 2.4.2. Distribution Function.- 2.4.3. Ion Temperature, Ion Current.- 2.5. Action of Radio Waves on the Ionosphere.- 2.5.1. lonization Balance in the Ionosphere.- 2.5.2. Effective Frequency of Electron and Ion Collisions-Fraction of Lost Energy.- 2.5.3. Electron and Ion Temperatures in the Ionosphere.- 2.5.4. Heating of the Ionosphere in an Alternating Electric Field.- 2.5.5.Perturbations of the Electron and Ion Concentrations.- 2.5.6. Artificial lonization of the Ionosphere-Heating of Neutral Gas.- 3. Self-Action of Plane Radio Waves.- 3.1. Simplification of Initial Equations.- 3.1.1. Nonlinear Wave Equation.- 3.1.2. Nonlinear Geometrical Optics of a Plane Wave.- 3.2. Effect of Nonlinearity on the Amplitude and Phase of the Wave.- 3.2.1. Self-Action of a Weak Wave.- 3.2.2. Self-Action of a Strong Wave.- 3.2.3. Self-Action of Waves in the Case of Artificial lionization.- 3.3. Change of Wave Modulation.- 3.3.1. Weak Wave.- 3.3.2. Change of Amplitude Modulation of Strong Wave.- 3.3.3. Phase Modulation.- 3.3.4. Nonlinear Distortion of Pulse Waveform.- 3.4. Generation of Harmonic Waves and Nonlinear Detection.- 3.4.1. Frequency Tripling.- 3.4.2. Nonlinear Detection.- 3.5. Self-Action of Radio Waves in the Lower Ionosphere.- 4. Interaction of Plane Radio Waves.- 4.1. Cross Modulation.- 4.1.1. Weak Waves.- 4.1.2. Strong Perturbing Wave.- 4.1.3. Resonance Effects near the Electron Gyrofrequency.- 4.2. Interaction of Unmodulated Waves.- 4.2.1. Interaction of Short Pulses.- 4.2.2. Change in the Absorption of a Wave Propagating in a Perturbed Plasma Region.- 4.2.3. Generation of Waves with Combination Frequencies.- 4.3. Radio Wave Interaction in the Lower Ionosphere.- 4.3.1. Cross Modulation.- 4.3.2. Fejer's Method.- 4.3.3. Nonstationary Processes in the Interaction of Strong Radio Waves.- 5. Self-Action and Interaction of Radio Waves in an Inhomogeneous Plasma.- 5.1. Inhomogeneous Electric Field in a Plasma.- 5.1.1. Fundamental Equations.- 5.1.2. Distribution of Density and Temperatures in Plasma.- 5.2. Kinetics of Inhomogeneous Plasma.- 5.2.1. Kinetic Coefficients. Elementary Theory.- 5.2.2. Kinetic Theory.- 5.2.3. Fully Ionized Plasma.- 5.3. Modification of the F Region of the Ionosphere by Radio Waves.- 5.3.1. Modification of the Electron Temperature and of the Plasma Concentration.- 5.3.2. Radio Wave Reflection Region.- 5.3.3. Growth and Relaxation of the Perturbations.- 5.4. Focusing and Defocusing of Radio Wave Beams.- 5.4.1. Nonlinear Geometrical Optics.- 5.4.2. Defocusing of Narrow Beams.- 5.4.3. Mutual Defocusing.- 5.4.4. Thermal Focusing in the Lower Ionosphere.- 6. Excitation of Ionosphere Instability.- 6.1. Self-Focusing Instability.- 6.1.1. Spatial Instability of a Homogeneous Plasma.- 6.1.2. Instability in the Wave-Reflection Region.- 6.2. Resonant Absorption and Resonance Instability.- 6.2.1. Langmuir Oscillations in an Inhomogeneous Plasma.- 6.2.2. Excitation of Plasma Waves.- 6.2.3. Resonance Instability.- 6.2.4. Absorption of Ordinary Radio Waves.- 6.3. Parametric Instability.- 6.3.1. Langmuir Oscillations of a Plasma in an Alternating Field.- 6.3.2. Parametric Excitation of Langmuir Oscillations.- 6.3.3. Parametric Instability in the Ionosphere.- 6.3.4. Dissipative Parametric Instability.

Slow-wave launching at the lower hybrid frequency using a phased waveguide array

Abstract: The coupling efficiency of a phased multi-waveguide structure (the "Grill") designed to launch HF-waves at the lower hybrid resonance to heat large toroidal plasmas, while satisfying the accessibility condition, is studied. To find the reflection and transmission coefficients, as well as the k||-spectrum of the excited field, the waveguide field, represented as a superposition of eigenmodes, is matched to the field in the plasma, which is evaluated on the assumption of a linear density profile near the plasma edge. It is found that the reflection coefficient can be made acceptably low and is not sensitively dependent on the plasma parameters. It is concluded that it is possible to design a Grill capable to launch lower hybrid waves at the power level required for the ignition of a reactor plasma.

Very long optical paths in air

Abstract: Two different multiple traversal optical systems are described; one gives the longest paths, the other the best compensation for vibration and misalignment problems. In the first, seven mirrors in a near confocal arrangement permit a large aperture beam of light to pass through a restricted volume for a discrete and very large number of times. A rectangular array of images corresponding to different numbers of passes appears on four mirrors at one end of the system. At the other end, three mirrors form the array and illuminate each image in it from one or more different directions. The possible numbers of passes are (4mn − 2)k + 2, where m and n are any integers representing, respectively, the number of columns and half the number of rows in the array. k is the number of different directions from which the array is illuminated. Geometrically, the beam may be isolated after thousands of passes; practically, the number is limited by reflection losses. In the second system the addition of four diagonal mirrors to a White cell converts the two lines of images on the single mirror to a rectangular array of images, almost squaring the maximum possible number of passes. With multiples of four rows of images in the array, the position of the output image is invariant to small errors in alignment of the mirrors.

Dielectric compound parabolic concentrators.

Abstract: where θm a x is the angular acceptance (half-angle) and n is the index refraction of the collector relative to the sur­ rounding medium. This concentration is the maximum permissable by physical principles. The CPC is a nonimaging light funnel that derives its characteristic optical properties from the specific shape of the external wall, which is made specularly reflecting. The diameters of these structures are generally large relative to the wavelength of light. We have also investigated models of certain visual receptors, which strikingly resemble the compound parabolic shape and wherein the specularity was achieved by total internal reflection. In these examples, chosen to simulate the conditions found in nature, a frac­ tion of the light rays leaks out because they fail to satisfy the condition for total internal reflection. The novel suggestion in this communication is the obser­ vation that for certain values of parameters (of consider­ able practical importance), the interface between the CPC and the surround becomes a perfect total internal reflec­ tion mirror that permits no leakage of radiation. This re­ sult is unexpected because the condition for maximal con­ centration [Eqs. (1) and (2)], which determines the shape of the external wall, and the condition for total internal re­ flection (angle of incidence exceeds the critical angle) have no a priori connection. Incident rays that lie within the angular acceptance (θmax) of the trough CPC are refracted into an elliptic cone of semiminor angle θmg' and semimajor angle θc, where

Effect of surface stress on wave propagation in solids

Abstract: In this paper we consider an elastic half‐space whose free surface is an elastic surface capable of supporting its own stress field. This surface stress is a function of surface strain and is related to the stress in the interior of the body by a nonclassical boundary condition. We here study, within the framework of the appropriate linearized theory, the reflection of plane harmonic waves by the free surface. We show that at very high frequencies the presence of surface stress results in a marked departure from the classical theory.

On the adequacy of plane-wave reflection/transmission coefficients in the analysis of seismic body waves

Abstract: In order to estimate the effect (on body waves) of discontinuities within the Earth, it is common practice to use the theory for plane waves incident upon the plane boundary between two homogeneous half-spaces. The resulting reflection/P~ V conversion/transmission coefficients are shown here to he inaccurate for many problems of current interest. Corrected coefficients are needed, in particular, for cases where the discontinuity (upon which boundary conditions are to be applied) is near a turning point of the P- or S-wave rays, or if one of these rays intersects the discontinuity at a near-grazing angle. Adequate corrections, based upon the Langer approximation to a full wave theory, are shown to be easily derived in practice. The method is first to write out the plane-wave coefficients as a rational polynomial, in sines and cosines of the angles of incidence upon the boundary, and second to introduce a multiplicative factor for each cosine. The new factors depart from unity only when the associated cosine tends to zero; i.e., when a turning point is approached. They incorporate all the corrections required for curvature of the boundary, frequency dependence, and Earth structure (velocity gradients) near the boundary.

On the Absorption, Reflection and Transmission of Solar Radiation in Cloudy Atmospheres

Abstract: Band-by-band calculations have been carried out to evaluate the reflection, absorption and transmission of solar radiation by cloud layer and model cloudy atmospheres in the entire solar spectrum. The radiation transfer program is based on the discrete-ordinate method with applications to inhomogencous atmospheres. The gaseous absorption in scattering atmospheres is taken into account by means of exponential fits to the total band absorption based on laboratory measurements. Thick clouds such as nimbostratus. and cumulonimbus reflect 80–90% and absorb 10–20% of the solar radiation incident upon them. The reflection and absorption of a fair weather cumulus with a thickness of 0.45 km are about 68–85% and 4–9%7p, respectively. A thin stratus, whose thickness is 0.1 km, reflects about 45–72% and absorbs about 1–6% of the solar flux incident on the cloud top. The reflection of a 0.6 km thick altostratus is about 57–77%, with a larger absorption of 8–15%. A number of aircraft observations reveal that ...

Step discontinuities on dielectric waveguides

Abstract: Reflection, transmission and radiation properties of a step discontinuity on a dielectric surface waveguide are calculated The method used involves bounding the open waveguide with perfect conductors Results are compared with those given by previous authors

Ultrasonic bounded beam reflection and transmission effects at a liquid/ solid‐plate/liquid interface

Abstract: Schlieren techniques are used to show that bounded beam reflection effects occur at liquid/solid‐plate/liquid (L/SP/L) interfaces which are analogous to the bounded beam reflection effects reported previously at liquid/solid (L/S) interfaces. At L/SP/L interfaces, nongeometric effects are shown to be present in both the reflected and transmitted beams when the incident angle of an ultrasonic beam corresponds to the Lamb angle. In addition, similarities between wave phenomena at L/SP/L interfaces and L/S interfaces are presented which suggest that the description of bounded beam reflection derived by Bertoni and Tamir for a L/S interface can be qualitatively applied to the L/SP/L interface case. This theory is shown to account for the lateral extent to which a leaky Lamb surface wave, excited by mode conversion, propagates.Subject Classification: [43]35.54; [43]20.40, [43]20.30.

Swept-frequency microwave Q-factor measurement

Abstract: Modern swept-frequency network analysers readily display complex reflection and transmission coefficients as functions of frequency. Methods, applicable to both 1- and 2-port cavities, are presented for the convenient extraction of cavity Q-factor information from the frequency variation of reflection coefficient amplitude and/or phase. The methods are extended to cases where the coupling circuit is lossy.

Microwave ice detector

Abstract: A system for detecting ice on exterior surfaces of aircraft by transmitting a relatively low power microwave electromagnetic signal into a dielectric layer functioning as a surface waveguide, and monitoring the signals transmitted into and reflected from the waveguide. The waveguide includes a termination element which is mismatched with the waveguide impedance, resulting in partial or total reflection of the microwave energy from the remote end of the waveguide. As ice builds up on the surface waveguide, the impedance or reflection characteristics of the composite waveguide comprising the ice layer and the permanent surface waveguide give a reliable indication of the presence and location of the ice. The reflection characteristics are conventionally monitored utilizing a dual directional coupler and a reflectometer.

Effects of sea‐ice ridges on sound propagation in the Arctic Ocean

Abstract: An environmental/acoustic model of sound propagation in the Arctic Ocean, which accounts for reflection losses from ridged sea ice, has been developed. In this model sea‐ice ridges are represented as infinitely long, randomly distributed, elliptical half‐cylinders. Under‐ice reflection losses for acoustic wavelengths either large or small compared to ridge dimensions are computed from theoretical equations as a function of average keel depth and width, number of ridges/km, and grazing angle. Numerical values of under‐ice reflection loss as a function of grazing angle are then incorporated into ray‐theoretical computations of transmission loss assuming a single sound‐ speed profile which is characteristic of the central Arctic Ocean. The validity of the concepts and approximations, the limitations of the model, and the accuracy of coincident measurements of environmental and acoustic parameters required to validate the model are discussed. To illustrate the predictions and accuracy of the model under diver...

Device for the non-dispersive optical determination of the concentration of gas and smoke components

Abstract: A method and apparatus for non-dispersive optical determination of gas and smoke components in a mixture by reflection and detection of radiation, of a different wavelength for each component, through the mixture, wherein the radiation is periodically intercepted before it enters the mixture and reflected direct to the photo-receiver and the measurement signals are divided by the stored direct signals.

Total backscattering of keV light ions from solid targets in single-collision approximation

Abstract: The reflection of light ions from heavy random targets has been calculated within the single-collision approximation on the basis of essentially the same physical model as Schiott's adaptation of the LSS range theory to light ions. An accurate effectivepower approximation has been utilized to evaluate a number of physical quantities relating to reflected ions under the assumption of Thomas-Fermi scattering. Analytical results as well as universal curves are presented for reflected-energy spectra integrated over ejection angle, particle and energy reflection coefficients, and quantities derived from these. Good agreement with experimental results is obtained for e≳, where e is Lindhard's energy parameter. The results are compared with those from previous calculations on the basis of transport theory and computer simulation. An estimate is given of the single-collision tail of the light-ion range profile. Qualitative corrections for beam attenuation and recoil energy loss are presented in appendices.

Device for observing an object

Abstract: A device for observing an object such as, for example, a mask, wafer, and so forth to be used in a printer for IC and LSI, and including a flat reflection surface and an inclined reflection surface having a certain inclination with respect to the flat reflection surface, by which light beam reflected at the flat reflection surface is removed by filter means to make it possible to observe only the inclined reflection surface of the object.

Exact theory of te-wave scattering from blazed dielectric gratings

Abstract: We present an exact description of scattering of an incident plane wave with te-polarization at an interface between two dielectric media that is deformed by a grating with triangularly shaped teeth. The theory employs an expansion in plane waves outside of the grating region and describes the field in the grating region as a double Fourier series expansion. The results of this theory are represented graphically. That blazing provides substantial discrimination of the scattering process in favor of beams scattered into one or the other of the two media is shown. The exact theory is used to check an approximation for the effective reflection plane that is useful for future applications of the theory to scattering by gratings of guided waves in thin-film waveguides.

The interaction of a shock with a dust deposit

Abstract: The possibility is investigated that dust can be raised from a deposit over which a shock wave passes by the reflection of shock waves from the underlying surface. It is shown that dust is raised as a result of the rapid flow behind the shock rather than as a result of pressure waves passing through the layer. Dust-cloud profiles fit the ballistic trajectories of individual particles having an initial vertical velocity of about 4.5 m s-1.

Realization of a Relativistic Mirror: Electromagnetic Backscattering from the Front of a Magnetized Relativistic Electron Beam.

Abstract: An intense relativistic electron beam has been injected into a cylindrical drift tube containing a counterstreaming electromagnetic wave ${f}_{i}=9.3$ GHz and ${P}_{i}=170$ kW). Within a narrow range of axial magnetic field centered at 5 kG, a reflected wave at ${f}_{s}\ensuremath{\sim}40$ GHz was generated by the interaction of the beam with the incident wave. The reflected wave was observed to have a power of several hundred kilowatts (i.e., greater than the power of the incident wave) and a pulse duration on the order of nanoseconds. All observed experimental characteristics (viz. frequency shift, power amplification, pulse duration, and cyclotron resonance) were consistent with a model of reflection from the discontinuity in refractive index that is associated with an electron beam front near cyclotron resonance. This mechanism could be employed in a new class of short-pulse, ultrahigh power, tunable generators at millimeter and submillimeter wavelengths.

Polaritons in a spatially dispersive dielectric half space

Abstract: An exact microscopic theory of volume and surface polaritons is developed for a spatially dispersive dielectric half space. No dielectric function is postulated; instead a collection of terms which is designated such arises naturally in the course of solving the microscopic equations that describe the response of the molecules to an external driving field. The excited states of the crystal are assumed to be Frenkel excitons which are treated in the tight-binding approximation. All intermolecular interactions are assumed to be of the point-dipole type. Formulas are derived for the reflection of $s$- and $p$-polarized light from the dielectric at arbitrary angle of incidence. Formulas are also given for the reflection of light inside a prism separated from the dielectric by a small gap as in attenuated-total-reflection experiments used to detect surface modes. Model calculations, using ZnSe parameters, exploring the effect of spatial dispersion on the optical properties are described.

Reflection and refraction of an arbitrary electromagnetic wave at a plane interface

Abstract: Asymptotic approximations are obtained for the reflected and refracted fields that result when an arbitrary monochromatic electromagnetic wave is incident on a plane interface separating two linear, homogeneous, isotropic dielectrics. The results are the first one or two terms in the asymptotic expansion of the fields valid as the point of observation moves away from the interface a distance large compared to the wavelength in any fixed direction apart from certain specified critical angles. The approximations are obtained from the exact solutions by applying the method of stationary phase extended to allow for the nonstandard form of the integrands in the integral representations of the fields. Although the method is applicable only when the medium containing the point of observation is nonabsorbing, the results probably have more general applicability.

Electromagnetic scattering of an arbitrary plane wave by a wire mesh with bonded junctions

Abstract: A doubly infinite set of linear equations for the currents has been found valid for a wire mesh with bonded junctions without imposing any junction conditions. However, the convergence of the solution is greatly improved by building junction discontinuity conditions into the current representation. Using such a modified solution, numerical results are generated to illustrate the dependence of reflection and transmission coefficients on various parameters.

Method and apparatus for optical method of measuring rail displacement

Abstract: For optically measuring rail displacement, a light projector with a slit plate, a reflection mirror for light projection, a reflection mirror for light reception and a light receptor with a slit plate are installed at specified distances from one another on the underside of the body of a track inspection car on both sides in the longitudinal direction thereof. The light projector, the reflection mirror for light projection, the reflection mirror for light reception and the light receptor are arranged so that the light emitted from the light source in the light projector passes through the slit and, being reflected by the reflection mirror for light projection, is converged onto a measuring axis connecting the points as to which measurement is being made on the opposed rails which constitute the track at at least one of the rails to form a bright spot or band of light. The light receptor receives only the light from the rails at said measuring axis via the reflection mirror for light reception and then the slit in said receptor. In the light receptor a deviation of the reference measuring points indicated by movement of the bright spot or band during the running of the track inspection car along the track is detected; and by comparing the deviation with the position of said reference measuring points when the rails are in the correct position, the rail displacement can be measured.

The vertical array in reflection seismology—some experimental studies

Abstract: There are several advantages in using vertical arrays for recording reflected signal. Signal-to-noise ratio can be controlled to any desired level when the noise is due to scattering from layers shallower than the depth to the array. By the use of vertical arrays, the band width of useable seismic energy can be increased, events can be properly identified, the signal that eventually produces near surface induced multiples can be measured, as well as the direct pulse radiated from the source and its accompanying ghosts. A field test documents these predictions.

Laser feedback: its effect on laser frequency

Abstract: To estimate the effect of laser feedback, a simple mirror system is considered and the effect on the frequency calculated. The analytical approach used is the same as that used in multifilm calculations. The mirrors are considered in sequence. The complex, Fresnel, amplitude reflection coefficient in conjunction with the next mirror is used to calculate the Fresnel reflection coefficient from the last three mirrors, and so on. This process is continued until the output mirror of the laser is reached and the complex reflection coefficient for the output mirror and all mirrors beyond is determined.

Infrasound from convective storms. III. Propagation to the ionosphere

Abstract: We model mathematically the spectral features of infrasound observed in the ionosphere and believed to be radiated by severe thunderstorms. We explain the dominant 2–5‐min wave period as an effect of atmospheric filtering; shorter periods are excessively attenuated by absorption in transit to the ionosphere, and longer periods are attenuated in portions of the atmosphere where the waves are evanescent because their frequencies are below the acoustic cutoff. An observed spectral ’’fine structure’’ within the 2–5‐min band is explained in terms of resonant interactions between the waves and the atmospheric temperature structure. Accurate quantitative modeling of all these details of the storm‐to‐ionosphere transmission coefficient requires numerical integration of the acoustic‐gravity wave equation, including the effects of ground reflection, absorption, and partial reflections in the atmosphere.Subject Classification: [43]28.30.