Modulation transfer in Doppler broadened Λ system and its application to frequency offset locking

We investigate modulation transfer through pump induced atomic coherence in pump-probe spectroscopy of Doppler broadened medium of cesium atoms. The mechanism of modulation transfer is discussed for a three level Λ configuration under slow frequency modulation. Modulation transfer is demonstrated by performing frequency modulation spectroscopy (FMS) on a sub-natural linewidth (<2 MHz) electromagnetically induced transparency (EIT) signal. Here the pump laser is modulated by acousto-optic frequency modulation and the modulation is transferred to the probe laser through atomic coherence. Finally the probe laser is locked on the first derivative spectrum of EIT signal. Such atomic frequency offset locking system totally removes the necessity of direct modulation of laser frequency, so that the spectral resolution is limited only by the practical linewidth of the laser systems. Moreover it provides a novel way to eliminate the additional frequency and intensity noise associated with direct frequency dithering, which may limit the experimental resolution.     

Dynamic multiscaling in two-dimensional fluid turbulence

We obtain, by extensive direct numerical simulations, time-dependent and equal-time structure functions for the vorticity, in both quasi-Lagrangian and Eulerian frames, for the direct-cascade regime in two-dimensional fluid turbulence with air-drag-induced friction. We show that different ways of extracting time scales from these time-dependent structure functions lead to different dynamic-multiscaling exponents, which are related to equal-time multiscaling exponents by different classes of bridge relations; for a representative value of the friction we verify that, given our error bars, these bridge relations hold.     

On-chip methane sensing by near-IR absorption signatures in a photonic crystal slot waveguide

We demonstrate a 300?μm long silicon photonic crystal (PC) slot waveguide device for on-chip near-infrared absorption spectroscopy, based on the Beer-Lambert law for the detection of methane gas. The device combines slow light in a PC waveguide with high electric field intensity in a low-index 90?nm wide slot, which effectively increases the optical absorption path length. A methane concentration of 100?ppm (parts per million) in nitrogen was measured.     

The magnetic field dependence of the structural transition temperature in La3S4 and La3Se4

The magnetic field dependence of the structural transition temperature T_m from the cubic to the tetragonal phase has been determined for single crystals of La₃S₄ and La₃Se₄. The observed field dependence of T_m can be accounted for by the band Jahn-Teller model of the coupling of an e_g-band to the shear mode of the cubic lattice without invoking any coupling to acoustic or optical phonons.     

Solutions of Yang's EuclideanR-gauge equations and self-duality

Under some assumptions and transformations of variables, Yang's equations forR-gauge fields on Euclidean space lead to conformally invariant equations permitting one to obtain infinitely many other solutions from any solution of these conformally invariant equations. These conformally invariant equations closely resemble the mathematically interesting generalized Lund-Regge equations. Some exact solutions of these conformally in variant equations are obtained. Except for some singular situations, these solutions are self-dual.     

Multidimensional optimization of finite difference schemes for Computational Aeroacoustics

Because of the long propagation distances, Computational Aeroacoustics schemes must propagate the waves at the correct wave speeds and lower the isotropy error as much as possible. The spatial differencing schemes are most frequently analyzed and optimized for one-dimensional test cases. Therefore, in multidimensional problems such optimized schemes may not have isotropic behavior. In this work, optimized finite difference schemes for multidimensional Computational Aeroacoustics are derived which are designed to have improved isotropy compared to existing schemes. The derivation is performed based on both Taylor series expansion and Fourier analysis. Various explicit centered finite difference schemes and the associated boundary stencils have been derived and analyzed. The isotropy corrector factor, a parameter of the schemes, can be determined by minimizing the integrated error between the phase or group velocities on different spatial directions. The order of accuracy of the optimized schemes is the same as that of the classical schemes, the advantage being in reducing the isotropy error. The present schemes are restricted to equally-spaced Cartesian grids, so the generalized curvilinear transformation method and Cartesian grid methods are good candidates. The optimized schemes are tested by solving various multidimensional problems of Aeroacoustics.     

Incompressibility of strange matter

Strange stars (ReSS) calculated from a realistic equation of state (EOS), that incorporate chiral symmetry restoration as well as deconfinement at high density [Phys. Lett. B 438 (1998) 123; Phys. Lett. B 447 (1999) 352, Addendum; Phys. Lett. B 467 (1999) 303, Erratum; Indian J. Phys. B 73 (1999) 377] show compact objects in the mass radius curve. We compare our calculations of incompressibility for this EOS with that of nuclear matter. One of the nuclear matter EOS has a continuous transition to ud-matter at about five times normal density. Another nuclear matter EOS incorporates density dependent coupling constants. From a look at the consequent velocity of sound, it is found that the transition to ud-matter seems necessary.     

Ermakov systems,Noether's theorem and the Sarlet-Bahar method

We derive invariants for a nonlinear equation of motion containing arbitrary functions. The method employed is the recently discussed direct method of Sarlet and Bahar. The resulting invariants are a special case of Ermakov invariants. We compare these results to the results obtained by applying Noether's theorem to the same equation of motion.