Nirmal K. Viswanathan

Bio: Nirmal K. Viswanathan is an academic researcher from University of Hyderabad. The author has contributed to research in topics: Polarization (waves) & Physics. The author has an hindex of 21, co-authored 97 publications receiving 2134 citations. Previous affiliations of Nirmal K. Viswanathan include Facultad de Ciencias Exactas y Naturales & Center for Advanced Materials.

Surface relief structures on azo polymer films

Abstract: All optical fabrication of Surface Relief Grating (SRG) on azobenzene functionalized polymer films is reviewed in this article. The uniqueness of the single step erasable photofabrication of large amplitude surface relief structures on azo polymer films is mainly due to the photoisomerization and photoanisotropic behavior of the azobenzene group. The design and synthesis of several classes of suitable azobenzene functionalized polymers for the SRG formation is presented. Experimental studies are carried out in a systematic manner to understand the chemical and physical intricacies involved in the SRG formation process. Structural requirements and their limitations for the efficient fabrication of SRGs on azo functionalized polymer films are also discussed. Understanding the fundamental mechanism of SRG formation on the azo functionalized polymer films enables us to make use of these structures in a variety of applications.

A Detailed Investigation of the Polarization-Dependent Surface-Relief-Grating Formation Process on Azo Polymer Films

Abstract: We have carried out two-beam interference experiments to form surface-relief gratings (SRGs) on azo polymer films under different polarization combinations. The mechanism of SRG formation on azobenzene chromophore functionalized polymer films has been shown to depend on both the spatial variation of the intensity as well as the polarization state of the incident field pattern. The treatment presented in this paper clearly defines the intensity and polarization distribution across the two-beam interference region for different polarization configurations of the interfering beams. The efficient photoisomerization process due to the spatial variation of the optical field renders the material anisotropic and the surface mobile. The simultaneous presence of a component of electric field gradient in the grating vector direction results in large-modulation-depth SRGs. We have carried out this investigation in one class of prototypical amorphous epoxy-based azo polymer thin films. Our results confirm that efficient SRG formation on azo functionalized polymer film requires photoinduced anisotropy and a component of optical field gradient in the direction of the grating vector.

Photofabrication of Surface Relief Grating on Films of Azobenzene Polymer with Different Dye Functionalization

Abstract: Photofabrication of surface relief grating (SRG) on very high-Tg and lower-Tg azobenzene functionalized polymers was investigated. Polymers with different degrees of functionalization were designed and synthesized to understand the chemical and physical intricacies involved at the molecular level in the photofabrication of SRG. The systematic study examined the influence of three important parameters: the degree of azo functionalization, the irradiating light intensity, and the initial film thickness. From the experimental results, we establish that the writing behavior of photofabricated SRG depends on the degree of azo functionalization. The effective critical intensity of the irradiating light was found to be independent of the degree of functionalization. Threshold behavior for the deformation process as a function of the degree of functionalization was established. The observed film thickness dependence of the SRG formation is discussed within the framework of existing fluid mechanics model. The the...

Spin-Hall effect and circular birefringence of a uniaxial crystal plate

Abstract: The linear birefringence of uniaxial crystal plates has been known since the 17th century, and it is widely used in numerous optical setups and devices. Here we demonstrate, both theoretically and experimentally, the fine lateral circular birefringence of such crystal plates. We show that this effect is a novel example of the spin-Hall effect of light, i.e., a transverse spin-dependent shift of the paraxial light beam transmitted through the plate. The well-known linear birefringence and the new circular birefringence form an interesting analogy with the Goos–Hanchen and Imbert–Fedorov beam shifts that appear in the light reflection at a dielectric interface. We report experimental observation of the effect in a remarkably simple system of a tilted half-wave plate and polarizers using polarimetric and quantum-weak-measurement techniques for beam-shift measurements. In view of much recent interest in spin–orbit interaction phenomena, our results could find applications in modern polarization optics and nanophotonics.

Azo Polymer Multilayer Films by Electrostatic Self-Assembly and Layer-by-Layer Post Azo Functionalization

Abstract: This work focuses on the development of a novel method for molecular level assembly and processing of multilayer azo polymer films. Poly(acrylic acid)-based precursor anilino-functional polymer was...

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Synthetic molecular motors and mechanical machines.

Abstract: The widespread use of controlled molecular-level motion in key natural processes suggests that great rewards could come from bridging the gap between the present generation of synthetic molecular systems, which by and large rely upon electronic and chemical effects to carry out their functions, and the machines of the macroscopic world, which utilize the synchronized movements of smaller parts to perform specific tasks. This is a scientific area of great contemporary interest and extraordinary recent growth, yet the notion of molecular-level machines dates back to a time when the ideas surrounding the statistical nature of matter and the laws of thermodynamics were first being formulated. Here we outline the exciting successes in taming molecular-level movement thus far, the underlying principles that all experimental designs must follow, and the early progress made towards utilizing synthetic molecular structures to perform tasks using mechanical motion. We also highlight some of the issues and challenges that still need to be overcome.

Principles Of Optics Electromagnetic Theory Of Propagation Interference And Diffraction Of Light

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