ABSTRACT
An investigation of oblique plane-wave electromagnetic scattering from active dielectric films reveals the existence of anomalously large resonances that occur at discrete plane-wave angles of incidence. These resonances may be understood from a leaky-wave phase-matching condition whose predictions for the first few modes agree to within a few percent of those obtained from a rigorous treatment using Maxwell's equations. Enhancement in the scattered-field intensities of the order of 100 was observed in experiments using finite-diameter pump and probe laser beams and active films as thin as 6 microm.
ABSTRACT
Amplification of light propagating as bound modes of a multimode fiber through evanescent wave coupling is reported. Experiments have been performed by immersing sections of a stripped fiber 2-20 cm long in a Kiton red dye solution which is pumped by the evanescent fields of a cw Ar-ion laser also propagating as bound modes of the fiber. Gain coefficients as high as 0.02/cm have been observed by a 633-nm He-Ne probe beam when pumped by a 5-W laser. Numerical calculations obtained by performing a Taylor series expansion of the eigenvalue equation for a cylindrical waveguide with a small active component in the cladding region show that modes near cutoff can exhibit gains 60% or higher, approaching those assumed for the cladding region.
ABSTRACT
A truncated spherical lens geometry is evaluated for layered lenses with various index profiles to determine power coupling efficiency between an LED and an optical fiber. The equations for the efficiency calculation through multiple boundaries are discussed, and numerical results are presented for optical fibers with numerical aperture values of 0.14, 0.23, and 0.35. The layered Luneburg profile is found to give the highest efficiency when the lens and fiber have a significantly larger size than the LED. The layered Maxwell fisheye profile is most efficient when the lens, fiber, and LED are of similar radius.
ABSTRACT
The scattering properties of active particles are studied and compared with those of particles with a complex conjugate (passive) index of refraction. It is shown that the extinction cross section of active particles is zero at certain frequencies and that only at certain frequency bands it is amplified. For most frequencies, the interference between diffracted and refracted waves causes the extinction cross section to behave like that of passive particles. A comparison of backscattered and forwardscattered intensities between active and passive particles with n(a) = n(p) * shows that as +/- Im(n) ? + infinity the intensities converge to the same value. For nonsymmetric scatterers, such as cylindrical fibers of elliptic cross section, it is shown that in the resonance region the major portion of the scattered field is not in the forward direction. In addition, the ratio of backscattered to forward scattered intensity is found to be greater than unity for active media for certain frequencies beyond the low frequency region.
ABSTRACT
The glory ray and the rainbow are analyzed by considering the scattering of light from inhomogeneous particles. It is shown that melting ice crystals may be strong contributors to the glory ray. Geometrical optics is used to investigate and catalog a wide variety of particle inhomogeneities which support rainbow and glory rays.
