Resonant holographic interferometry for species concentration measurements with saturated anomalous dispersion

A double-exposure resonant holographic interferometry measurement technique for full-field, instantaneous species is presented. This technique utilizes tuned pulsed dye lasers, separate reference beams, and a corrective holographic optical element. The resulting interferogram fringes represent the species number density of interest with variations in the bulk refractive index due to the temperature field automatically subtracted. Expressions for relating resonant absorption with fringe shift are disclosed. The relations suggest that RHI is well suited for optically dense media and long path lengths, where absorption measurements can be difficult. A saturation related modification of the dispersion near a broadened resonant transition is described. The depopulation of the ground state due to saturation by the probe beam causes an asymmetric modification of the resonant refractive index, which when convolved over the probing beam does not affect the measured fringe shift as measured by RHI. Resonant interferometry is demonstrated as an accurate and quantitative measure of the concentration of sodium vapor in a low pressure cell. Furthermore, as a combustion diagnostic, RHI is demonstrated on a minor combustion species, OH, in a nonpremixed slot burner. PACS 33.70-w; 42.40.Kw; 82.33.Vx     

The x-ray anomalous dispersion and optical rotation in the crystalline solid solution NaClO3: NaBrO3

Sodium chlorate and sodium bromate crystals of thes ame structural configuration have opposite senses of optical rotation. It is also known that these halates exhibit continuous miscibility in solid solution. In the present work, the conjecture of Bijvoet that in the solid solution of these halates, the crystalline configuration would continue itself, has been directly verified by two approaches: (i) by optical rotation measurements on single crystals which show an annulling trend in proportion with composition and (ii) by measuremerts of Bijvoet inequality for several reflections from a single crystal (rich in chlorate) which shows an agreeable trend with the calculated values for chlorate. This paper forms a part of Mohanlal’s thesis accepted by the Madurai University for the Ph.D. degree. We emphasize optical rotation is dextro, if the plane of polarisation is rotated clockwise, for an observer looking towards the source of light.     

Excitable front geometry in reaction-diffusion systems with anomalous dispersion

Two-dimensional excitable systems with anomalous dispersion provide a discrete set of interpulse distances for the stable propagation of planar wave trains. Numerical simulations show that the trailing front of a pulse pair can undergo transitions between these stable distances. In response to localized perturbations, the trailing front converges towards one of numerous, sigmoidal shapes. Their transition segments move at constant speeds and can collide and fuse with each other. A complementing kinematic analysis of the front dynamics yields a reaction-diffusion-like equation.     

Multiwavelength anomalous diffraction at high x-ray intensity

The multiwavelength anomalous diffraction (MAD) method is used to determine phase information in x-ray crystallography by employing anomalous scattering from heavy atoms. X-ray free-electron lasers (FELs) show promise for revealing the structure of single molecules or nanocrystals, but the phase problem remains largely unsolved. Because of the ultrabrightness of x-ray FEL, samples experience severe electronic radiation damage, especially to heavy atoms, which hinders direct implementation of MAD with x-ray FELs. Here, we propose a generalized version of MAD phasing at high x-ray intensity. We demonstrate the existence of a Karle-Hendrickson-type equation in the high-intensity regime and calculate relevant coefficients with detailed electronic damage dynamics of heavy atoms. The present method offers a potential for ab initio structural determination in femtosecond x-ray nanocrystallography.     

Theory of anomalous dispersion in a-Se

A theory of multiple trapping expressed in terms of generalized first-order transport equations is used to explain the change in dispersion with temperature of the photocurrent transients in a-Se. The theory is shown to be equivalent to the continuous-time random walk (CTRW) model of Scher and Montroll, and the hopping-time distribution function is computed for the CTRW model in terms of the trap parameters.     

Negative refractive index and anomalous dispersion

Media with negative index of refraction are discussed briefly within Sellmeier model. In particular, dispersion of light waves is found to be anomalous and the corresponding coefficient of material dispersion is found to be negative. In addition, the group index becomes negative.     

Transient anomalous dispersion in random walkers

A simple model of dispersive tracers which display a transient anomalous regime is presented. It is based on an ensemble of random walkers belonging to two independent populations characterized by different Lagrangian decorrelation times. Apart from short-time ballistic and long-time diffusive behavior, the dispersion shows anomalous scaling at intermediate times over a wide range of variability for the free parameters of the model.     

Demonstration of Faraday anomalous dispersion optical filter with reflection configuration

A narrow linewidth Faraday anomalous dispersion optical filter(FADOF)with reflection configuration is achieved for the first time based on the cesium(Cs)ground state 6S_1/2 to the excited state 6P_3/2 transition at 852 nm.Compared with the conventional FADOF with transmission configuration,reflection-type FADOF can greatly improve the transmittance of optical filter under the same experimental parameters,because it allows signal light to go and return through the atomic vapor cell.In our experiment,peak transmittance at Cs 6S_1/2 F=4-6P_3/2 transition is 81%for the reflection-type FADOF,and while 54%for the transmission-type FADOF when the temperature of Cs vapor cell and the axial magnetic field are 60℃and 19 G.The idea of this reflection-type FADOF design has the potential to be applied to the FADOF operating between two excited states to obtain higher transmittance.     

Tracking waves and vortex nucleation in excitable systems with anomalous dispersion

We report experimental results obtained from a chemical reaction-diffusion system in which wave propagation is limited to a finite band of wavelengths and in which no solitary pulses exist. Wave patterns increase their size through repeated annihilation events of the frontier pulse that allow the succeeding pulses to advance farther. A related type of wave dynamics involves a stable but slow frontier pulse that annihilates subsequent waves in front-to-back collisions. These so-called merging dynamics give rise to an unexpected form of spiral wave nucleation. All of these phenomena are reproduced by a simple, three-species reaction-diffusion model that reveals the importance of the underlying anomalous dispersion relation.     

反常色散材料光子晶体中光输运的光学控制

研究了光抽运对由铯原子蒸气构成的光子晶体的影响.研究发现,利用较弱光强的线抽运光即可显著地改变这种反常色散光子晶体的透射率.而利用圆偏振光抽运可以进一步降低抽运光的阈值,并在反常色散光子晶体中获得极大的法拉第旋转.反常色散光子晶体的这些特性为光控光开关的研究和制作提供了一条新途径.     

Transfer of information in an anomalous dispersion medium

The transfer of information and signal velocity in an anomalous dispersion medium are studied. We propose that the discontinuous points in the envelop and its derivatives of any order are the information carried by a pulse different from others. The signal velocity will not exceed the speed of the shift of these discontinuous points. We study the propagation of pulses with a triangle envelop and with the envelop made up by three pieces of quadratic curve in dilute, anomalous dispersion gas with double gain lines. The discontinuous points of the envelop, its first derivative, and its second derivative are shown to propagate with vacuum speed of light c in the medium. A criterion has been suggested to determine theoretically whether the distortion of a pulse can be ignored.     

Design of apochromatic telescope without anomalous dispersion glasses

A novel lens system with correction of secondary spectrum without using anomalous glasses is presented. The lens system comprises four separated lens components, with three of them being subapertures. Two examples of apochromatic telescope are presented, both with the use of typical normal glasses, namely crown K9 and flint F5 glasses, and low-cost slightly anomalous dispersion glasses. Secondary spectrum and other chromatic aberrations of the two design examples are corrected.     

Quantum effects with an x-ray free-electron laser

A quantum kinetic equation coupled with Maxwell's equation is used to estimate the laser power required at an x-ray free-electron laser (XFEL) facility to expose intrinsically quantum effects in the process of QED vacuum decay via spontaneous pair production. A 9 -TW-peak XFEL laser with photon energy of 8.3 keV could be sufficient to initiate particle accumulation and the consequent formation of a plasma of spontaneously produced pairs. The evolution of the particle number in the plasma will exhibit non-Markovian aspects of the strong-field pair production process, and the plasma's internal currents will generate an electric field whose interference with that of the laser leads to plasma oscillations.     

Measurements of anomalous dispersion by the interference fringe shift

A method of measurement of anomalous dispersion near spectral lines of absorption from interference fringe shifts is described. The sensitivity and accuracy of the method is analyzed and its advantage over the hook method is demonstrated. The system consists of Rozhdestvenskii's interferometer and a diffraction grating spectrometer. The device is adapted both to photo and photoelectric recording of the interference fringes.The technique is tested on the first resonance doublet of sodium with the wave lenghts 5890, 5896 Å. For the oscillator strengths ratio ?₅₈₉₀/?₅₈₉₆ we get 2.05±0.03.