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S R Seshadri

Publications and source records attributed to S R Seshadri.

15 recordsLinked to original sources
PubMed2007

Dynamics of the linearly polarized fundamental Gaussian light wave.

A continuous planar array of dipoles that are oriented in a particular direction and have an amplitude distribution that is Gaussian in the paraxial limit is introduced as a source for the fundamental Gaussian light wave. The radiation intensity of the Gaussian light wave is determined and its characteristics are analyzed. The universal Gaussian beam factor is deduced and identified as the radiation intensity of the scalar Gaussian wave. The total radiated power, the mean center of the localized wave, and the beam widths of the intensity distribution are obtained. The ratio of the power in the Gaussian wave to that in the corresponding paraxial Gaussian beam is used as a measure of the quality of the paraxial beam approximation. A limiting factor for the power ratio is introduced as an indicator for the acceptability of the paraxial beam approximation. The cross section and the beam widths of the localized light wave are investigated in the large and small kw0 limits, where k is the wavenumber and w0 is the beam waist at the input plane. The beam width of the full Gaussian wave is found to be less than that of the corresponding paraxial Gaussian beam both for the scalar Gaussian wave and for the Gaussian light wave.

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PubMed2006

Quality of paraxial electromagnetic beams.

The full wave theory of focused waves is developed and the radiation intensity distribution is determined. In the appropriate limit, the full wave theory correctly reproduces the paraxial beams. The limitations of paraxial beam theories are discussed. The method of treatment of full waves is presented with reference to the scalar Bessel-Gauss beam and wave. The necessary theoretical formulas for other beams and waves are also given. For the scalar Bessel-Gauss wave, the beam shape parameter can be adjusted to yield a flat-topped radiation pattern. The ratio of the power in the paraxial beam to that in the full wave is used as a parameter to measure the quality of the paraxial beam approximation. Lower-order waves are found to have better paraxial beam quality than do higher-order waves. The difference in the paraxial beam quality increases as kw0 is decreased where k is the wavenumber and w0 is the waist of the paraxial beam. The radiation patterns of waves are presented for some tightly focused waves.

Journal Article↗
PubMed2006

Self-interaction and mutual interaction of complex-argument Laguerre-Gauss beams.

A general method is presented for the determination of the time-averaged power associated with the self-interaction and the mutual interaction of cylindrically symmetric complex-argument Laguerre-Gauss beams. The method is also applied for the determination of two useful moments of the time-averaged Poynting vector.

Journal Article↗
PubMed2006

High-aperture beams: comment.

Clarifications are provided for the proper choice of the branch of a square-root function that is connected with the singularity on the focal plane occurring in the treatment by Sheppard on 'High-aperture beams' [J. Opt. Soc. Am. A18, 1579 (2001)]. The author's claim that the singularity is nonphysical is disputed.

Comment↗
PubMed2005

Complex-argument Laguerre-Gauss beams: transport of mean-squared beam width.

For the azimuthally varying complex-argument Laguerre-Gauss beams, the Fourier integral representation is used to obtain the time-averaged power and the transport equation for the mean-squared beam width. From the coefficients in the transport equation, two propagation parameters are derived and compared with the previous treatments.

Journal Article↗
PubMed2005

Beam dynamics of two modes propagating along the optic axis in a uniaxial crystal.

The Gaussian beam propagation in the direction of the optic axis of a uniaxial crystal is treated by the complex-source-point technique. At the input plane the electric field is linearly polarized. A particular superposition of the ordinary-mode and the extraordinary-mode beams is generated. The electrodynamics of the composite beam has features that are different from those of the two constituent beams. As a result of the anisotropy, on propagation, the cross-polarized component of the electric field is generated except along the beam axis; the cross section of the beam, which is circular at the input plane, becomes elliptical; and the mean squared width of the beam departs from the usual quadratic dependence on the distance from the waist in the direction of propagation.

Journal Article↗
PubMed2004

Effect of absorption on the spreading of a laser beam.

The propagation characteristics of the fundamental Gaussian laser beam in absorptive and active media are investigated. There is a general reduction in the spreading of the beam on propagation in both absorptive and active media. In addition, in an active medium there is a shift of the focal plane and a reduction in the waist size of the beam.

Journal Article↗
PubMed2003

Virtual source for a Hermite-Gauss beam.

A virtual source that generates a Hermite-Gauss wave of mode numbers m and n is introduced. An expression is obtained for this Hermite-Gauss wave. From this expression, the paraxial approximation and the first 3 orders of nonparaxial corrections for the corresponding paraxial Hermite-Gauss beam are determined. When both m and n are even, leading to maximum amplitude along the axis, the number of orders of nonvanishing nonparaxial corrections is found to be equal to (m + n)/2.

Journal Article↗
PubMed2003

Basic elliptical Gaussian wave and beam in a uniaxial crystal.

Electromagnetic beams in a uniaxial crystal are treated with emphasis on the extraordinary mode. A virtual source that generates a basic elliptical Gaussian wave propagating obliquely to the optic axis is identified. An exact expression is obtained for this basic elliptical Gaussian wave that simplifies to the corresponding basic elliptical Gaussian beam in the appropriate limit. In the direction of amplitude propagation, the paraxial result becomes identical to the exact result and the sum of all the nonparaxial contributions vanish. The characteristics of the basic elliptical Gaussian beam are illustrated with a numerical example. From the spectral representation of the basic Gaussian wave, the first three orders of nonparaxial corrections for the basic elliptical Gaussian beam are determined. The nonparaxial results reduce correctly to those of the fundamental Gaussian beam in an isotropic medium.

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PubMed2001

Electromagnetic theory of an open resonator.

Particular higher-order sources give rise to electromagnetic Gaussian beams, which are linearly polarized and have their maximum in the propagation direction. For this dipolar beam the cross-sectional shape changes in the propagation direction. Nodal surfaces exist on which the tangential component of the electric field vanishes in the standing wave that is formed by the two oppositely directed dipolar, electromagnetic Gaussian beams. These surfaces are identified as the mirror shapes for an open resonator that supports this standing wave. For standing waves that have a particular cross-sectional shape at the waist the cross section of the beam near the mirror surfaces is circular. The resonant frequencies for the fundamental transverse mode of such a resonator have been determined as a function of the geometry and the axial mode number. By a perturbation technique the resonant frequency of an open resonator with spherical mirrors has been obtained. This result is valid in only the paraxial approximation. Illustrative numerical results are included.

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PubMed2001

Polarization conversion by reflection in a thin-film grating.

A dielectric-film waveguide with a grating etched on its film-cover interface can be used as a polarization converter. The e wave can be converted into the h wave and vice versa if the guided wave is incident obliquely to the grating vector. The polarization converter is analyzed by use of a quasi-optic technique. A high degree of polarization-conversion efficiency is achieved by a suitable choice of the grating length. The Bragg angles of incidence and observation, the maximum polarization-conversion efficiency, and the frequency and the angular selectivity are all found to increase with an increase in the grating period. An illustrative numerical example is presented.

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PubMed2000

Average characteristics of partially coherent electromagnetic beams.

Average characteristics of partially coherent electromagnetic beams are treated with the paraxial approximation. Azimuthally or radially polarized, azimuthally symmetric beams and linearly polarized dipolar beams are used as examples. The change in the mean squared width of the beam from its value at the location of the beam waist is found to be proportional to the square of the distance in the propagation direction. The proportionality constant is obtained in terms of the cross-spectral density as well as its spatial spectrum. The use of the cross-spectral density has advantages over the use of its spatial spectrum.

Electromagnetic Phenomena↗