Magnetic Dipole Radiation

3 Key excerpts on "Magnetic Dipole Radiation"

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  Handbook of Wave and Field Physics (Concepts and Applications)

  • (Author)
  • 2014(Publication Date)
  • Academic Studio

    (Publisher)

  Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa . Therefore, as an oscillating electric field generates an oscillating magnetic field, the magnetic field in turn generates an oscillating electric field, and so on. These oscillating fields together form an electromagnetic wave. ________________________ WORLD TECHNOLOGIES ________________________ A quantum theory of the interaction between electromagnetic radiation and matter such as electrons is described by the theory of quantum electrodynamics. Properties Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This diagram shows a plane linearly polarized wave propagating from right to left. The electric field is in a vertical plane and the magnetic field in a horizontal plane. The physics of electromagnetic radiation is electrodynamics. Electromagnetism is the physical phenomenon associated with the theory of electrodynamics. Electric and magnetic fields obey the properties of superposition so that a field due to any particular particle or time-varying electric or magnetic field will contribute to the fields present in the same space due to other causes: as they are vector fields, all magnetic and electric field vectors add together according to vector addition. For instance, a travelling EM wave incident on an atomic structure induces oscillation in the atoms of that structure, thereby causing them to emit their own EM waves, emissions which alter the impinging wave through interference. These properties cause various phenomena including refraction and diffraction.

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  Classical Electrodynamics

  • Tung Tsang(Author)
  • 1998(Publication Date)
  • WSPC

    (Publisher)

  184 Magnetic Dipole and Electric Quadrupole Radiation Sec. 7.3 of the radiation is concentrated inside the main peak where -2jt/N=0 in the y-direction in Fig. 7.3(a). (The other possibility 6=0 is excluded, since Eo=0 at 6=0 according to eq. (7.38).) The radiation is emitted predomi-nantly in a direction perpendicular to the orientation of the array. Such a system is known as a broadside array. (We can think of the array as a World War II battleship or cruiser where the individual antennas are the guns or the turrets mounted on the centerline of the ship which is the x-axis. It is desirable to have broadside fire toward y-axis since all guns can fire toward the target. The end-fire is along x-axis and should be avoided since only the turrets at the end of the ship can be fired toward the target.) As number N of antennas increase, the radiation intensity at the center goes up as N 2 and the angle of the radiation pattern becomes narrower as N 1 . A linear array of half-wave antennas which are spaced X/2 apart and which are driven with alternate phases has its main radiation maximum along =0 (x-axis). Such a system is known as an end-fire array. The details will be left as an exercise. 7.3. Magnetic Dipole and Electric Quadrupole Radiation In Sec. 7.1, we have studied the radiation from localized oscillating systems with current density J and charge density p e . We have derived the general result, eq. (7.13), which can then be used to calculate B and E from eqs. (7.3) and (7.4). For localized sources, we have Ir'klrl. For electric dipole (ED) radiation in Sec. 7.1, we have simplified eq. (7.13) into eq. (7.14) by neglecting r For many systems, the ED radiation may be forbidden by symmetry.

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  Atomic Structure and Lifetimes

  A Conceptual Approach

  • Lorenzo J. Curtis(Author)
  • 2003(Publication Date)
  • Cambridge University Press

    (Publisher)

  Since spin-changing transitions are forbidden in electric dipole transitions, the quantum number S is suppressed here. The M J and M J quantum numbers are projections with respect to an arbitrarily chosen quantization axis (specified, for example, by an anisotropic excitation mechanism). Thus the radiation into all 4 π steradians must be independent of the M J values for a field-free atom. However, the angular distribution and polarization of the radiation differs for the M J = 0 ( π radiation) and M J = ± 1 ( σ ± radiation). This can easily be understood from a simple model. For a classically radiating oscillating dipole aligned with the z -axis at the origin of a spherical coordinate system, the plane of polarization (the direction of the electric field) lies along the direction of the ϑ unit vector, and has an angular distribution proportional to sin 2 ϑ (as described in the proverb “under the candle it is darkest”). As shown in Fig. 6.1, a general three-dimensional aligned system can be characterized by three mutually perpendicular dipoles of intensities I σ / 2, I σ / 2 and I π . Here z is the quantization axis of the excitation process. The dipoles along the x -and y -axes correspond to the σ ± radiation and the dipole along the z -axis corresponds to the π radiation. The origin of this notation lies in the polarization of the Zeeman components that are observed in the presence of a magnetic field, as could be impressed here along the z -axis. Relative to a plane formed by the z -axis and the propagation vector of the photon (the y – z plane in Fig. 6.1), the polarization of the m = 0 radiation will be parallel ( π ) to the plane, and that of the m = ± 1 will be perpendicular ( σ ± , for senkrecht) to the plane. It is possible to discriminate among these components using a linear polarizer. 116 6 Electric dipole radiation x I σ I π z y 2 I σ 2 3 + ϑ / / Fig.

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