V P Nayyar

Two-point resolution of Gaussian aperture operating in partially coherent light using various resolution criteria

We have investigated the dependence of two-point resolution by an aberration-free Gaussian aperture on the real part of the complex degree of coherence. The Sparrow and the modified Rayleigh criteria have been used for the partially coherent optical systems, and a comparison between them has been made. To reveal important information concerning the characteristics of the image, the irradiance distribution from two mutually partially coherent point sources has also been computed.

Self-trapping and self-focusing of an elliptical laser beam in a collisionless magnetoplasma

The authors have studied the self-trapping and self-focusing-defocusing of an elliptically shaped laser beam in a magnetoplasma. The critical self-trapping power of the beam for the ordinary mode is twice the critical power for the extraordinary mode. On both sides of the critical power required for self-trapping, there are separate values of the critical power for the x-dimension as well as for the y-dimension of the beam. At and above the critical value for the x-dimension, the beam defocuses in both directions while at and below the critical value for the y-dimension, it self-focuses in both directions. Self-trapping is also observed in the case of the ordinary mode at a critical value of the external magnetic field for any power value.

Diffraction by truncated-Gaussian annular apertures

A theoretical study of the diffraction of a plane Gaussian wave truncated by annular aperture. Kirchhoffs integral has been evaluated to obtain the irradiance distribution in the diffracted field. Results of the calculations conducted for optimum size of the annular aperture for various values of the Gaussian spot size have been presented graphically.

Self-focusing and self-defocusing of elliptically shaped Gaussian laser beams in plasmas

Presents a study of the self-focusing and self-defocusing of elliptically shaped Gaussian laser beams in collisional and collisionless plasmas. The non-linear dependence of the dielectric constant inside a collisional plasma is due to inhomogeneous heating of energy carriers and in a collisionless plasma it is due to the ponderomotive force. It is found that the beam gets focused at different points in different planes, exhibiting the effect of astigmatism. In certain power regions considered, the beam either converges or defocuses in both the directions, while in some other regions of the power spectrum one dimension of the beam focuses while the other defocuses. The beam also propagates in an oscillatory waveguide.

Resolution of a centrally obstructed circular aperture in partially coherent light

A theoretical study has been made to investigate the dependence of resolution on the coherent properties of the light source in the case of an aberration-free annular aperture operating in partially coherent light. The composite intensity curves have been presented for separations greater than that for Sparrow incoherent light and also for separations in the region of the Rayleigh limit. Even the best resolution shows some variation for these separations.

Thermal Focusing of Elliptically Shaped Optical Beams in Dielectrics

The authors report a study on thermal lensing of an elliptically shaped optical beam in an absorbing dielectric media. It is found in the case of lead glass (with dn/dT, the rate of change of refractive index with temperature, positive) that the beam gets focused at different focal points in different directions, exhibiting the effect of astigmatism. There are several critical points, below the lowest of which there is no self-focusing, but at higher powers one dimension focuses while the other defocuses. Above the higher critical power, both dimensions self-focus, and the dimensionless beam-width parameters f1 and f2 for x and y focusing reach different minima corresponding to different self-focusing distances, beyond which both dimensions continue to diverge. In the case of crystal NaCl (where dn/dT is ne gative), both dimensions of the beam defocus, whatsoever the power of the incident beam.

The effect of non-uniform illumination on the two-point resolution of a microscope using a semi-transparent and π-phase annular aperture

Presents a theoretical study of the effects of non-uniform illumination on the two-point resolution of a semi-transparent and pi -phase annular aperture microscope. It has been observed that the limiting separation exhibits an oscillatory character around the incoherent limit. The best resolution is obtained in a good contrast image when the illumination is of the type (1- rho 2)-12/, rho being the radial coordinate in the lens aperture.

Cross-focusing of Mixed Mode Operation in a Collisional Plasma

This paper presents a study of the nonlinear propagation of a mixture of two degenerate modes (TEM00 and TEM10) of a high power laser beam in a collisional plasma. The non-linear dependence of the dielectric constant inside the collisional plasma is due to non-uniform redistribution of carriers on account of their inhomogeneous heating. The focusing effects have been studied for different power ratios of the two modes and the absorption effects have also been considered. In certain power regions considered the beam either converges or defocuses in both the directions, while in some other defined regions of the power spectrum one dimension of the beam focuses and the other defocuses.

Diffraction by a semitransparent and pi -phase annular aperture illuminated by a Gaussian laser beam

Expressions have been derived for the irradiance distribution in the diffracted field of an aberration-free semitransparent and pi -phase aperture illuminated by a Gaussian laser beam. Calculations have been done for various values of the real part of the complex amplitude transmittance of the central region of the aperture. The results have been presented graphically.

Influence of surface errors on the modulation sensitivity of a Fabry-Perot electro-optic type wide-band modulator

The influence of asymmetrical random polishing and symmetrical parabolic surface imperfections on the modulation sensitivity of a Fabry-Perot electrooptic type wide-band modulator has been investigated. The modulation sensitivity of the modulator has been found to decrease significantly in presence of the errors. For amplitudes, of the error functions small in comparison to the wavelength of incident radiation, the loss in modulation sensitivity has been found to be greater for random error.