Somnath Ghosh

Bio: Somnath Ghosh is an academic researcher from Indian Institute of Technology, Jodhpur. The author has contributed to research in topics: Microstructured optical fiber & Optical fiber. The author has an hindex of 28, co-authored 287 publications receiving 3318 citations. Previous affiliations of Somnath Ghosh include University of Calcutta & Indian Institute of Science.

Synthesis of 3‐Methyl‐4‐arylmethylene Isoxazole‐5(4H)‐ones by Visible Light in Aqueous Ethanol.

Abstract: A highly efficient methodology for the synthesis of 3-methyl-4-arylmethylene-isoxazole-5(4H)-ones has been developed by visible light induced multicomponent reaction of aromatic aldehydes, ethyl acetoacetate, hydroxylamine hydrochloride, and sodium acetate in aqueous ethanol sans any phase transfer catalyst or promoter.

Formation of nanoscale metallic structures on cupric nitride thin film surface by the impact of 200 MeV Au15+ ions

Abstract: Cupric nitride films deposited on borosilicate glass and Si substrates by RF reactive sputtering are irradiated by 200 MeV Au 15+ ions from Pelletron accelerator. On-line elastic recoil detection analysis (ERDA) technique shows a large depletion of N (∼75% depletion) from the films due to electronic sputtering effect of heavy ion whereas the copper content remains unchanged. This observation is associated with a sharp rise in sample ladder current signifying an enhancement of electron emission from the film during irradiation. The surface of the as deposited film studied by atomic force microscope (AFM) shows nanodimensional grain formation. Conducting AFM (CAFM) measurements show that at certain regions (10–30 nm) of the irradiated film surface a rapid rise of current (∼9000 pA) takes place. Enhancement of electron emission together with conducting AFM measurements lead us to conclude that conductivity of the surface enhances due to formation of nanodimensional metallic zones under Au ion impact. The entire process is understood on the basis of thermal spike model of ion–solid interaction.

Durability Study of Geopolymer Paste Blended with Blast Furnace Slag

Abstract: In this program consequence of incorporating blast furnace slag on mechanical properties and durability of resulting fly ash geopolymer paste sample was investigated. The program consisted immersion of geopolymer samples having percentage blast furnace slag ranging from 10 to 20 of fly ash in a 10% magnesium sulfate solution up to a period of 15 weeks and evaluation of its resistance in terms visual appearance, change in weight and compressive strength at regular interval. Addition of blast furnace slag considerably improved mechanical properties and durability of geopolymers paste.

Successive switching among four states in a gain-loss-assisted optical microcavity hosting exceptional points up to order four

Abstract: The implementation of exceptional points (EPs), a special type of topological singularities, has emerged as a new paradigm for engineering the quantum-inspired or wave-based photonic systems. Even though there exists a range of investigations on EPs of order two and three (say, EP2s and EP3s, respectively), the hosting of fourth-order EPs (EP4s) in any real system and the exploration of associated topological features are lacking. Here we have designed a simple Fabry-P\'erot type gain-loss-assisted open optical microcavity to host EPs up to order four. The scattering-matrix formalism has been used to analyze the microcavity numerically. With the appropriate modulation of the gain-loss profile in the same cavity geometry, we have encountered multiple different orders of EPs by investigating the simultaneous interactions among four coupled cavity states via level-repulsion phenomena. Besides affirming the second-order and third-order branch-point behaviors of the embedded EP2s and EP3s, the fourth-order branch-point functionality of an EP4 has been manifested by encircling three connecting EP2s simultaneously in the closed gain-loss parameter space. We have established a unique successive state-switching phenomenon among four coupled states by implementing such an EP4-encirclement scheme in the system's parameter space. The proposed scheme indeed offers potential applications in state-switching and control in quantum-inspired integrated photonic circuits, where the presence of an EP4 serves as a new light manipulation tool.

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 …

Exceptional points in optics and photonics.

Abstract: BACKGROUND Singularities are critical points for which the behavior of a mathematical model governing a physical system is of a fundamentally different nature compared to the neighboring points. Exceptional points are spectral singularities in the parameter space of a system in which two or more eigenvalues, and their corresponding eigenvectors, simultaneously coalesce. Such degeneracies are peculiar features of nonconservative systems that exchange energy with their surrounding environment. In the past two decades, there has been a growing interest in investigating such nonconservative systems, particularly in connection with the quantum mechanics notions of parity-time symmetry, after the realization that some non-Hermitian Hamiltonians exhibit entirely real spectra. Lately, non-Hermitian systems have raised considerable attention in photonics, given that optical gain and loss can be integrated as nonconservative ingredients to create artificial materials and structures with altogether new optical properties. ADVANCES As we introduce gain and loss in a nanophotonic system, the emergence of exceptional point singularities dramatically alters the overall response, leading to a range of exotic functionalities associated with abrupt phase transitions in the eigenvalue spectrum. Even though such a peculiar effect has been known theoretically for several years, its controllable realization has not been made possible until recently and with advances in exploiting gain and loss in guided-wave photonic systems. As shown in a range of recent theoretical and experimental works, this property creates opportunities for ultrasensitive measurements and for manipulating the modal content of multimode lasers. In addition, adiabatic parametric evolution around exceptional points provides interesting schemes for topological energy transfer and designing mode and polarization converters in photonics. Lately, non-Hermitian degeneracies have also been exploited for the design of laser systems, new nonlinear optics phenomena, and exotic scattering features in open systems. OUTLOOK Thus far, non-Hermitian systems have been largely disregarded owing to the dominance of the Hermitian theories in most areas of physics. Recent advances in the theory of non-Hermitian systems in connection with exceptional point singularities has revolutionized our understanding of such complex systems. In the context of optics and photonics, in particular, this topic is highly important because of the ubiquity of nonconservative elements of gain and loss. In this regard, the theoretical developments in the field of non-Hermitian physics have allowed us to revisit some of the well-established platforms with a new angle of utilizing gain and loss as new degrees of freedom, in stark contrast with the traditional approach of avoiding these elements. On the experimental front, progress in fabrication technologies has allowed for harnessing gain and loss in chip-scale photonic systems. These theoretical and experimental developments have put forward new schemes for controlling the functionality of micro- and nanophotonic devices. This is mainly based on the anomalous parameter dependence in the response of non-Hermitian systems when operating around exceptional point singularities. Such effects can have important ramifications in controlling light in new nanophotonic device designs, which are fundamentally based on engineering the interplay of coupling and dissipation and amplification mechanisms in multimode systems. Potential applications of such designs reside in coupled-cavity laser sources with better coherence properties, coupled nonlinear resonators with engineered dispersion, compact polarization and spatial mode converters, and highly efficient reconfigurable diffraction surfaces. In addition, the notion of the exceptional point provides opportunities to take advantage of the inevitable dissipation in environments such as plasmonic and semiconductor materials, which play a key role in optoelectronics. Finally, emerging platforms such as optomechanical cavities provide opportunities to investigate exceptional points and their associated phenomena in multiphysics systems.