Comment on "Neutron Interferometric Observation of Noncyclic Phase"

A critique of a recent experiment [Wagh et.al., Phys.Rev.Lett.81, 1992 (7 Sep 1998)] to measure the noncyclic phase associated with a precessing neutron spin in a neutron interferometer, as given by the Pancharatnam criterion, is presented. It is pointed out that since the experiment measures, not the noncyclic phase itself, but a quantity derived from it, it misses the most interesting feature of such a phase, namely the different sign associated with states lying in the upper and the lower hemispheres, a feature originating in the existence of a phase singularity. Such effects have earlier been predicted and seen in optical interference experiments using polarization of light as the spinor [Bhandari, Phys.Rep.281, 1 (Mar 1997)].Comment: 5 pages, 0 figures, submitted to Phys.Rev.Let

Reciprocity constraints on the matrix of reflection from optically anisotropic surfaces

We derive certain constraints on the reflection matrix for reflection from a plane, nonmagnetic, optically anisotropic surface using a reciprocity theorem stated long ago by van de Hulst in the context of scattering of polarized light. The constraints are valid for absorbing and chiral media and can be used as tools to check the consistency of derived expressions for such matrices in terms of the intrinsic parameters of the reflecting medium as illustrated by several examples.Comment: 14 pages, 2 figures, submitted to Jour. Opt. Soc. Am.

On singularities of the mixed state phase

A recent proposal of Sjoqvist et.al. to extend Pancharatnam's criterion for phase difference between two different pure states to the case of mixed states in quantum mechanics is analyzed and the existence of phase singularities in the parameter space of an interference experiment with particles in mixed states pointed out. In the vicinity of such singular points the phase changes sharply and precisely at these points it becomes undefined. A closed circuit in the parameter space around such points results in a measurable phase shift equal to 2n\pi, where n is an integer. Such effects have earlier been observed in interference experiments with pure polarization states of light, a system isomorphic to the spin-1/2 system in quantum mechanics. Implications of phase singularities for the interpretation of experiments with partially polarized and unpolarized neutrons are discussed. New kinds of topological phases involving variables representing decoherence (depolarization) of pure states are predicted and experiments to verify them suggested.Comment: 4 pages Latex, 1 postscript figure; submitted to Physical Review Letters 12 Dec 2000; Revised on 13 August 200

Cancellation of simple optical anisotropies without use of a Faraday mirror

We first derive the round-trip Jones matrix for double passage through a reciprocal optical medium by means of reflection off a plane mirror that could be optically anisotropic. We then show that if a medium with only linear birefringence and linear dichroism is placed between a pair of orthogonal quarterwave plates with principal axes at 45 deg to that of the medium and the sandwich is placed in front of an isotropic mirror it behaves, under double passage, like an isotropic medium. We describe a simple liquid crystal device that behaves, in reflection, as an isotropic medium whose refractive index can be varied by application of an electric field, thus acting as a phase only modulator for light in any polarization state.Comment: 9 pages, 2 figure

Non Government Organization in India – Challenges and Perspectives

NGO’s are Non Governmental Organization’s are usually refer for organization which is not part of Government thought could be founded by the Government. The primary objective of this organization is to provide public service. NGO’s are non profit making voluntary, service oriented for development oriented originations, either for the benefit of members or of other members of the population or any agencies. NGO’s include groups and institutions i.e. entirely and largely independent of Government. This organization that have primarily human interior or co-operatives, rather than commercial objectives. They are private social agencies in industrial countries that support development of groups organised regionally or nationally and member of groups in village. NGO’s are non profit making organization i.e. constituted with a vision by group. The main installation purpose of this organization is to provide public service and not for profit making organization. The achievements and success of NGOs in various field and the excellent work done by them in specific areas is no dough  tremendous task that has help to meet the changing needs of the social system. NGO’s sector in India is expending day to day social events. NGO’s are facing different problems which defer for reason to reason, organization to organization NGO’s include charitable and religious association that mobilised private funds for development distribute food and family planning service and also promote community organization. They are also including independent co-operative, community associations, water user societies, woman groups and pastoral association