Biswas B.,Raja Ramanna Center for Advanced Technology
Review of Scientific Instruments | Year: 2013
A solenoid magnetic field model is presented that describes the on axis field by a parameter of its hard edginess and axial half-width at half-maximum field, which universally define its spherical aberration without solving the ray equation. The model shows an increase in spherical aberration from real soft edge fields to hard edge models, as used in beam tracking. It compares well with existing field models. It simply and accurately finds the spherical aberration in many types of solenoids. © 2013 AIP Publishing LLC.
Saini V.K.,Raja Ramanna Center for Advanced Technology
Applied Optics | Year: 2013
Laser-induced optogalvanic (OG) signal oscillations detected in miniature neon glow discharge plasma are investigated using a discharge equivalent-circuit model. The damped oscillations in OG signal are generated when a pulsed dye laser is tuned to a specific neon transition (1s5 ? 2p2) at 588.2 nm under the discharge conditions where dynamic resistance changes its sign. Penning ionization via quasi-resonant energy transfer collisions between neon gas atoms in metastable state and sputtered electrode atoms in ground state is discussed to explain the negative differential resistance properties of discharge plasma that are attributed to oscillations in the OG signal. The experimentally observed results are simulated by analyzing the behavior of an equivalent discharge-OG circuit. Good agreement between theoretically calculated and experimental results is observed. It is found that discharge plasma is more sensitive and less stable in close vicinity to dynamic resistance sign inversion, which can be useful for weakoptical- transition OG detection. © 2013 Optical Society of America.
Roy S.B.,Raja Ramanna Center for Advanced Technology
Journal of Physics Condensed Matter | Year: 2013
We show that the first order magneto-structural phase transitions observed in various classes of magnetic solids are often accompanied by useful multi-functional properties, namely giant magneto-resistance, magneto-caloric effect and magneto-striction. We highlight various characteristic features associated with a disorder influenced first order phase transition namely supercooling, superheating, phase-coexistence and metastability, in several magnetic materials and discuss how a proper understanding of the transition process can help in fine tuning of the accompanied functional properties. Magneto-elastic coupling is a key element in this first order phase transition, and methods need to be explored for maximizing the contributions from both the lattice and the magnetic degree of freedom while simultaneously minimizing the thermomagnetic hysteresis loss. An analogy is also drawn with the first order phase transition observed in dielectric materials and vortex matter of type-II superconductors. © 2013 IOP Publishing Ltd.
Kamal C.,Raja Ramanna Center for Advanced Technology |
Ezawa M.,University of Tokyo
Physical Review B - Condensed Matter and Materials Physics | Year: 2015
Recently, phosphorene, a monolayer honeycomb structure of black phosphorus, was experimentally manufactured and has attracted rapidly growing interest. Motivated by phosphorene, here we investigate the stability and electronic properties of the honeycomb structure of the arsenic system based on first-principles calculations. Two types of honeycomb structures, buckled and puckered, are found to be stable. We call them arsenenes, as in the case of phosphorene. We find that both buckled and puckered arsenenes possess indirect gaps. We show that the band gap of puckered and buckled arsenenes can be tuned by applying strain. The gap closing occurs at 6% strain for puckered arsenene, where the bond angles between the nearest neighbors become nearly equal. An indirect-to-direct gap transition occurs by applying strain. Specifically, 1% strain is enough to transform puckered arsenene into a direct-gap semiconductor. We note that a bulk form of arsenic called gray arsenic exists which can be used as a precursor for buckled arsenene. Our results will pave the way for applications to light-emitting diodes and solar cells. © 2015 American Physical Society.
Jayabalan J.,Raja Ramanna Center for Advanced Technology
Journal of the Optical Society of America B: Optical Physics | Year: 2011
The higher-order nonlinear optical response of a composite medium having metal nanoparticles is usually attributed to that originating from the third-order nonlinearity of the metal. In this article, the time dependence of hot-electron contribution to the third-, fifth-, and seventh-order nonlinear absorption coefficients of the composite medium has been studied. By comparing the results of the calculation with that of the experiments, it has been shown that the higher-order nonlinearities originating from the hot electrons of metal do contribute to the measured higher-order nonlinear absorption coefficients of the composite material. © 2011 Optical Society of America.