Propagation Of Electromagnetic Radiation Research Articles

A mode coupling theory for a parabolic index optical fibre whose axis deviates from straightness

The mathematical similarity of the paraxial scalar wave equation used in optical fibre theory and the Schrödinger equation of quantum mechanics is described. The Green's function of the paraxial wave equation is used in a formal description of the propagation of electromagnetic radiation along a fibre and the mode coupling properties of a fibre with imperfections. The equations are solved explicitly for a fibre with a parabolic refractive index profile whose axis deviates arbitrarily from straightness.

The depolarization of light by interstellar magnetic turbulence

The application of stochastic perturbation theory to the propagation of electromagnetic radiation in a cold plasma with random magnetic inhomogeneities leads to a field equation for the propagation of the coherence matrix of the field. This has nine independent components since the longitudinal mode must be included. An exact solution is obtained leading to simple expressions for the Stokes parameters as a function of distance and one physical parameter characterizing the interstellar plasma. While the total polarization decays exponentially, it is found that the ratio of elliptical to linear polarization increases with propagation distance in an exponential fashion. Using current estimates of the properties of the interstellar plasma it is expected that this effect whereby the polarization ellipse opens into a circle should be clearly evident for sources at distances of the order of 10. parsec It is suggested that this phenomenon might be used as a distance scale for certain objects.

Submillimeter Microwave Spectrum ofH2O16

The absorption spectrum of water vapor, in addition to giving information about the structure and properties of the water molecule, is of practical importance because of the effects of water vapor on the propagation of electromagnetic radiation. However, precise measurements of only 6 ground-vibrational-state transitions of ${\mathrm{H}}_{2}^{16}$O have been reported in the microwave region. We report the measurement of nine new rotational transitions of ${\mathrm{H}}_{2}^{16}$O and the remeasurement to higher accuracy of the four previously known submillimeter lines. The frequencies of the newly observed transitions are (in Mc/sec) ${10}_{2,9}$\ensuremath{\leftarrow}${9}_{3,6}$, 321225.644; ${7}_{5,3}$\ensuremath{\leftarrow}${6}_{6,0}$, 437346.667; ${6}_{4,3}$\ensuremath{\leftarrow}${5}_{5,0}$, 439150.812; ${7}_{5,2}$\ensuremath{\leftarrow}${6}_{6,1}$, 443018.295; ${6}_{4,2}$\ensuremath{\leftarrow}${5}_{5,1}$, 470888.947; ${5}_{3,3}$\ensuremath{\leftarrow}${4}_{4,0}$, 474689.127; ${6}_{2,4}$\ensuremath{\leftarrow}${7}_{1,7}$, 488491.133; ${5}_{3,2}$\ensuremath{\leftarrow}${4}_{4,1}$, 620700.807; and ${2}_{1,1}$\ensuremath{\leftarrow}${2}_{0,2}$, 752033.227. These transitions have been measured with a submillimeter-wave spectrometer which employs a klystron-driven crystal harmonic generator and a 1.6\ifmmode^\circ\else\textdegree\fi{}K InSb photoconducting detector. With this work, the lines contributing the major portion of the atmospheric absorption of water vapor in the region up to 800 Gc/sec have been precisely measured.

Indices of Refraction, Susceptibilities, and Correlation Functions

The previously derived phenomenological Maxwell equation [R. L. Fulton, J. Chem. Phys. 50, 3355 (1969)] is used to give a general description of the propagation of electromagnetic radiation in media which are invariant under translations and rotations. The connections between the complex indices of refraction and correlation functions are derived with a minimum of hypotheses about the nature of the medium. It is shown that the commonly assumed connection between the complex angle of rotation of plane polarized light in optically active media and correlation functions is more general than the usual derivation indicates. The correct inclusion of the frequency dependence of the index of refraction in the connection between the optical parameters and the Fourier transform of the dipole–dipole correlation function is shown to give rise to qualitative and quantitative changes of infrared band shapes, including the narrowing of lines, in the cases of C6F6 (1527 cm−1), C6H6 (678 cm−1), and CHCl3 (760 cm−1). The contribution of the 1527-cm−1 band of C6F6 to the time dependent dipole–dipole correlation function is found, obtaining a relaxation time of τr = 1.07 psec when the frequency dependence of the index of refraction is correctly included as compared to a value of τr = 0.58 psec when the variation is disregarded. The correlation functions arising from the cosine and the sine Fourier transforms of the 522-cm−1 band of CH3I are determined, the comparison of which with the dipole–dipole correlation function illustrates the necessity of retaining both transforms in the calculation of the correlation function.

Wave Propagation in Stratified Absorbing or Amplifying Media*

Solutions are found to the wave equations that describe the steady-state propagation of electromagnetic radiation through an isotropic inhomogeneous medium capable of an irreversible exchange of energy with the radiation field. These solutions are obtained for media in which the inhomogeneity consists of a slow variation of the relevant material parameters along one particular direction in space. The mechanism by means of which energy is dissipated in matter may involve the conductivity of the medium, or by magneticor electric-dipole allowed transitions in the medium.

Magneto-spatial dispersion effects on the propagation of electro-magnetic radiation in crystals

The lowest order combined effects of wave vector (spatial dispersion) and applied magnetic fields on the propagation of light in cubic crystals and along the optic axis of uniaxial crystals are investigated phenomenologically. In general, these effects, which are only observable in crystals lacking a center of symmetry, lead either to a second order elliptical modification of the circularly polarized modes or to a second order change in the wave velocities without modification of the polarization. In specific situations, the lowest order effects correspond to an induced linear birefringence and an induced elliptical polarization which are simply related to the crystal parameters. Among cubic crystals, these effects should be observable in zincblende type crystals.

Propagation of Electromagnetic Radiation through a Resonant Medium

The propagation of electromagnetic radiation through a resonant medium is studied. The slowly varying envelope of the electromagnetic field is assumed to have a slowly varying phase in addition to a slowly varying amplitude. The nonlinear coupled equations of motion are solved exactly under rather general assumptions. Three classes of solutions are obtained; two of them reduce to the solutions of Crisp and of McCall and Hahn when the slowly varying phase is zero. Because of the gauge invariance of the equations of motion, there is a term proportional to the vector potential in addition to the terms of its space and time derivatives in the equation describing the evolution in time of the electromagnetic field. Hence, a characteristic frequency exists in the infrared region below which the wave number becomes imaginary.

On the possibility of birefringence in a moving plasma

In a recent paper Lusignan [1963] has carried out a calculation which indicates that the velocity of propagation of electromagnetic radiation in a moving plasma should depend on the direction of polarization. When the propagation is perpendicular to the plasma velocity V, Lusignan finds a phase velocity for electric field polarization perpendicular to V slightly greater than that for polarization parallel to V. As the problem can be viewed in the rest frame of the plasma, where there is no preferred direction of polarization, it is clear that Lusignan's result is not tenable. The purpose of this short note is to re-examine Lusignan's treatment and to reconcile it with the requirement of no birefringence imposed by special relativity.

Wave Propagation in an Active Dielectric Slab

An analysis is made of the propagation of electromagnetic radiation in a dielectric slab having a negative electrical conductivity, sandwiched between semiinfinite regions having the same dielectric constant but positive conductivities. The threshold conditions corresponding to zero attenuation for waves propagating in the plane of the slab are determined. For slab thicknesses that are small, compared with a wavelength, the most easily excited wave is polarized with its electric vector perpendicular to the plane of the slab but for thicker active regions the threshold is independent of polarization. These results are compared with observations of stimulated emission in p-n junction lasers.

Wave Propagation in a Coaxial Glow Discharge

The propagation of electromagnetic radiation from 500 to 4200 Mc in a coaxial cage transmission line passing through a cylindrical discharge chamber is investigated experimentally. Measurements were conducted in argon, helium, and nitrogen gas at pressures between 0.09 mm Hg and 2 mm Hg for a discharge-electromagnetic radiation interaction length of 30.48 cm. The results are compared with theory using a Lorentzian model to describe the electron motion in the presence of the RF field. A graphical method for determining the plasma frequency and electron momentum transfer collision frequency from measurements of the power transmission coefficient at two different radio frequencies is discussed. A comparison is made between the plasma frequency determined by this method and that obtained by the use of a cylindrical Langmuir probe. The electron momentum transfer collision probability is calculated from the RF and probe data.

Hazards Due to Total Body Irradiation by Radar

Experimental work by others at 10 cm wavelength has shown that irreversible damage to the eye is caused by electromagnetic radiation, if the energy flux is in excess of about 0.2 watt/cm2. Intolerable temperature rise, due to total body irradiation may be anticipated for flux values in excess of 0.02 watts/cm2. Hence a discussion of hazards due to total body irradiation is of primary interest. This paper presents data which analyze the mode of propagation of electromagnetic radiation into the human body and resultant heat development. The two quantities which are considered in detail are: 1) coefficient, which characterizes the percentage of airborne electromagnetic energy as absorbed by the body, and 2) distribution of heat sources in skin, subcutaneous fat, and deeper situated tissues. It is shown: 1) The percentage of absorbed energy is near 40 per cent at frequencies much smaller than 1000 and higher than 3000 mc. In the range from about 1000 to 3000 mc the coefficient of absorption may vary from 20 to 100 per cent. 2) Radiation of a frequency below 1000 mc will cause deep heating, not well indicated by the sensory elements in the skin and, therefore, considered especially dangerous. Radiation whose frequency exceeds 3000 mc will be absorbed in the skin. Radiation of a frequency between 1000 and 3000 mc will be absorbed in both body surface and in the deeper tissues, the ratio being dependent on parameters involved.