Second-order optical susceptibility in doped III-V piezoelectric semiconductors in the presence of a magnetostatic field

A detailed analytical investigation of second-order optical susceptibility has been made in moderately doped III-V weakly piezoelectric semiconductor crystal, viz. n-InSb, in the absence and presence of an external magnetostatic field, using the coupled mode theory. The second-order optical susceptibility arises from the nonlinear interaction of a pump beam with internally generated density and acoustic perturbations. The effect of doping concentration, magnetostatic field and pump intensity on second-order optical susceptibility of III-V semiconductors has been studied in detail. The numerical estimates are made for n-type InSb crystals duly shined by pulsed 10.6 μm CO₂ laser and efforts are made towards optimising the doping level, applied magnetostatic field and pump intensity to achieve a large value of second-order optical susceptibility and change of its sign. The enhancement in magnitude and change of sign of second-order optical susceptibility, in weakly piezoelectric III-V semiconductor under proper selection of doping concentration and externally applied magnetostatic field, confirms the chosen nonlinear medium as a potential candidate material for the fabrication of nonlinear optical devices. In particular, at B ₀ = 14.1 T, the second-order susceptibility was found to be 3.4 × 10^-7 (SI unit) near the resonance condition.     

Intensification of sonophotocatalytic degradation of p-nitrophenol at pilot scale capacity

Sonophotocatalysis involves the use of a combination of ultrasonic irradiation, ultraviolet radiation and a semiconductor photocatalyst, which enhances the rates of chemical reactions by the formation of enhanced amounts of free radicals. In the present work, the sonophotocatalytic degradation of p-nitrophenol has been investigated using low frequency ultrasound waves (25 kHz) with an acoustic power of 1 kW and UV tube of 11 W power rating at an operating volume of 7 L. The efficacy of combination of sonochemistry and photocatalysis has been initially compared with the individual operation of sonolysis and photocatalytic oxidation. The effect of operational conditions such as the initial p-nitrophenol concentration, pH and catalyst concentration on the extent of degradation has been investigated using sonophotocatalysis. The initial concentration of the pollutant was varied in the range 10 to 100 ppm whereas pH in the range of 2.5-11 and catalyst loading in the range of 0.5-4 g/l. Intensification studies have been carried out using hydrogen peroxide and Fenton chemistry. In all the systems investigated, maximum extent of degradation (94.6%) was observed for 10 ppm of p-nitrophenol initial concentration (w/v) using combination of sonophotocatalysis and optimum quantity of H(2)O(2). Use of Fenton chemistry also plays an effective role in enhancing the extent of degradation though the concentration of additive needs to be carefully adjusted in order to get maximum beneficial effects.     

Demonstration of the possibility of >100 Gbit/s transmission over 77 km of standard fibre using a super-step-chirped fibre grating dispersion compensator.

3.8 ps pulses at 1556 nm are reconstructed after transmission over 77 km of standard fibre using a 20 cm long super-step-chirped fibre Bragg grating. We show that good results can be obtained despite the fact that the grating was untrimmed and unapodised, even when the full 1.5 nm reflection bandwidth of the grating is used.     

Effect of anions on supramolecular architecture of benzimidazole-based ionic salts

The reaction of N,N,N′,N′-tetrakis-(1H,benzimidazol-2ylmethyl) propane-1,3-diamine (L) with different inorganic acids affords salts viz., LH₄ ⁴⁺·4ClO₄ ^?·H₂O (1), LH₄ ⁴⁺·4Cl^?·2H₂O (2), LH₄ ⁴⁺·2H₂PO₄ ^?·H₇P₃O₁₂ ^2?·3H₃PO₄ (3), LH₄ ⁴⁺·4NO₃ ^? (4), and 2LH⁺·2CF₃COO^?·5H₂O (5). The X-ray crystallographic studies revealed that the proton transfer occurred from acid to the ligand. It also demonstrated that different type of hydrogen bond between protonated ligand and anions is responsible for the supramolecular framework. The colorimetric test showed color change upon the addition of acids in the solution of the ligand. The photo-physical experiments suggested the fluorescence properties of ligand in the presence of acids.     

Limiting ionic conductivity and solvation dynamics in formamide

A self-consistent microscopic theory has been used to calculate the limiting ionic conductivity of unipositive rigid ions in formamide at different temperatures. The calculated results are found to be in good agreement with the experimental data. The above theory can also predict successfully the experimentally observed temperature dependence of total ionic conductivity of a given uniunivalent electrolyte in formamide. The effects of dynamic polar solvent response on ionic conductivity have been investigated by studying the time dependent progress of solvation of a polarity probe dissolved in formamide. The intermolecular vibration (libration) band that is often detected in the range of 100-200 cm(-1) in formamide is found to play an important role in determining both the conductivity and the ultrafast polar solvent response in formamide. The time dependent decay of polar solvation energy in formamide has been studied at three different temperatures, namely, at 283.15, 298.15, and 328.15 K. While the predicted decay at 298.15 K is in good agreement with the available experimental data, the calculated results at the other two temperatures should be tested against experiments.     

A variable-wavelength-based approach of phase retrieval for contrast transfer function based methods

X-ray phase-contrast imaging has emerged as an important method for improving contrast and sensitivity in the field of X-ray imaging. This increase in the sensitivity is attributed to the fact that, in the hard X-ray regime, the phase shift is more prominent as compared with the attenuation for materials having a low X-ray absorption coefficient. Among all the methods using the X-ray phase-contrast technique, in-line phase-contrast imaging scores over the other methods in terms of ease of implementation and efficient use of available X-ray flux. In order to retrieve the projected phase map of the object from the recorded intensity pattern, a large number of algorithms have been proposed. These algorithms generally use either the transport of intensity or contrast transfer function based approach for phase retrieval. In this paper it is proposed to use multiple wavelengths for phase retrieval using the contrast transfer function based formalism.     

Wideband wavelength conversion using double-pass cascaded χ:χ interaction in lossy waveguides

We report the wavelength conversion based on double-pass cascaded nonlinear interaction (χ⁽²⁾:χ⁽²⁾) of sum and difference frequency generation in quasi-phase matched lithium niobate waveguides and compare it with double-pass cascaded second harmonic generation and difference frequency generation with and without waveguide loss. It is shown that the efficiency decreases considerably even for the low-loss waveguide compared to the lossless one especially for long waveguides and to achieve the higher efficiency for the same length, the amount of the extra power to compensate the loss increases. Also, an increased detuning of pump wavelength is proposed to flatten the response with a small efficiency penalty. The detuning- and loss-compensating pump powers can be found using the design diagrams in which the criteria for the design of waveguide length and the assignment of pumps power to obtain the desired efficiency, ripple and bandwidth are presented assuming a 75-nm pump wavelength difference.