Simplified theory of optical nonlinearities in spin-polarized bulk GaAs

Apart from their intrinsic physical interest, spin-polarized many-body effects are expected to be important to the working of spintronic devices. A vast literature exists on the effects of a spin-unpolarized electron-hole plasma on the optical properties of a semiconductor. Here, we include the spin degree of freedom to model optical absorption of circularly polarized light by spin-polarized bulk GaAs. Our model is easy to implement and does not require elaborate numerics, since it is based on the closed-form analytical pair-equation formula that is valid in 3d. The efficacy of our approach is demonstrated by a comparison with recent experimental data.

Machine recognition of online handwritten Devanagari characters

In this paper, we describe a system for the automatic recognition of isolated handwritten Devanagari characters obtained by linearizing consonant conjuncts. Owing to the large number of characters and resulting demands on data acquisition, we use structural recognition techniques to reduce some characters to others. The residual characters are then classified using the subspace method. Finally the results of structural recognition and feature-based matching are mapped to give final output. The proposed system Ifs evaluated for the writer dependent scenario.

Structure and optical properties of Cd-substituted ZnO (Zn1-xCdxO) nanostructures synthesized by the high-pressure solution route

We report the synthesis of Cd-substituted ZnO nanostructures (Zn1-xCdxO with x up to approximate to 0.09) by the high-pressure solution growth method. The synthesized nanostructures comprise nanocrystals that are both particles (similar to 10-15 nm) and rods which grow along the [002] direction as established by transmission electron microscope (TEM) and x-ray diffraction (XRD) analysis. Rietveld analysis of the XRD data shows a monotonic increase of the unit cell volume with the increase of Cd concentration. The optical absorption, as well as the photoluminescence (PL), shows a red shift on Cd substitution. The line width of the PL spectrum is related to the strain inhomogeneity and it peaks in the region where the CdO phase separates from the Zn1-xCdxO nanostructures. The time-resolved photoemission showed a long-lived (similar to 10 ns) component. We propose that the PL behaviour of the Zn1-xCdxO is dominated by strain in the sample with the red shift of the PL linked to the expansion of the unit cell volume on Cd substitution.

Optical, Field-Emission, and Antimicrobial Properties of ZnO Nanostructured Films Deposited at Room Temperature by Activated Reactive Evaporation

ZnO nanostructures were deposited on flexible polymer sheet and cotton fabrics at room temperature by activated reactive evaporation. Room-temperature photoluminescence spectrum of ZnO nanostructured film exhibited a week intrinsic UV emission and a strong broad yellow-orange visible emission. TEM and HRTEM studies show that the grown nanostructures are crystalline in nature and their growth direction was indentified to be along [002]. ZnO nanostructures grown on the copper-coated flexible polymer sheets exhibited stable field-emissio characteristics with a threshold voltage of 2.74 V/mu m (250 mu A) and a very large field enhancement factor (beta) of 23,213. Cotton fabric coated with ZnO nanostructures show an excellent antimicrobial activity against Staphylococcus aureus bacteria (Gram positive), and similar to 73% reduction in the bacterial population is achieved compared to uncoated fabrics after 4 h in viability. Using a shadow mask technique, we also selectively deposited the nanostructures at room temperature on polymer substrates.

ESR study of dibarium copper formate tetrahydrate Part II. Optical absorption and temperature dependence of spin-hamiltonian parameters

The variations in certain spin-Hamiltonian parameters of the Cu++ ion in dibarium copper formate tetrahydrate with temperature have been studied. Optical absorption investigations on single crystals of the salt at room temperature and 90° K. are reported. The results are discussed in terms of a model in which vibronic mixing of certain electron levels of the Cu++ ion play an important role.

ESR and optical absorption studies in copper diethyldithiocarbamate

ESR investigations at X band and optical-absorption measurements have been reported in single crystals of copper (n) diethyldithiocarbamate Cu[S 2CN(C2H5)2]2 diluted to 0.2% with the corresponding zinc complex. The measurements have been made both at room and liquid-oxygen temperatures. ESR measurements gave the following values for the parameters in spin Hamiltonian g11=2.1085, g=2.023(6), A63= 142.4×10-4 cm-1, A65 = 152.0×10-4 cm-1, B = 22.4×10-4 cm-1, Q~3×10-4 cm-1. Polarized optical absorption study has made possible a proper assignment of the absorption bands to their corresponding transitions. This has led to information regarding the ordering of the MO levels of the complex. The coefficients used in the MO description of the complex have been calculated from the observed parameters. The results show that the metal ligand BIσ bond is purely covalent and that the out-of-plane w bonding is appreciably covalent whereas the in-plane Π bonding is ionic. Further, it is noted that the metal ligand binding is more covalent with sulfur as ligand than with oxygen or nitrogen.

The elastic properties of a group of optical glasses by the pulse echo set-up

The pulse-echo apparatus, designed and constructed by the author, has been used to reinvestigate the elastic properties of the eighteen optical glasses. The elastic constants are correct to 0·5%. The results are compared with the earlier investigation which utilised the optical method. The possible causes for large discrepancies observed are critically and briefly discussed. A qualitative interpretation of the results has been successfully attempted. The acoustic velocity increases with the decrease in lead and barium oxides and with increase in calcium oxide and boron trioxide components.

On self-interacting oligoribonucleotides. I. Absorption and optical rotatory dispersion of 2′-5′- and 3′-5′-oligoguanylic acids

A series of 2′-5′-oligoguanylic acids are prepared by reacting G(cyclic)p with takadiastase T1 ribonuclease and separating the products chromatographically. The 3′-5′-oligoguanylic acids are obtained by separating the products of alkaline degradation of 3′-5′-poly(G). The optical rotatory dispersion and hypochromism of both 2′-5′- and 3′-5′-oligoguanylic acids are studied at two different pH. The optical rotatory dispersion spectrum of 2′-5′-GpG is significantly different from that of 3′-5′-GpG. The magnitude of rotation of the long-wavelength peak of 2′-5′-GpG is larger than that of 3′-5′-GpG. This finding contradicts the explanation that the extra stability and more intense circular dichroism band of other 3′-5′-dinucleoside monophosphates is due to H-bond formation between 2′-OH and either the base or the phosphate oxygen. The end phosphate group has a marked effect on the spectrum of GpG between 230 and 250 mμ. In addition the optical rotatory dispersion spectra of 2′-5′ exhibit strong pH, temperature, and solvent dependence between 230 and 250 mμ. ΔH and AS for order ⇌ disorder transition is estimated to be 9.7 kcal/mole and 35.2 eu, respectively. The optical rotatory dispersion spectra of guanine-rich oligoribonucleotides, GpGpC, GpGpU, GpGpGpC, and GpGpGpU are compared to the calculated optical rotatory dispersion from the semiempirical expression of Cantor and Tinoco, using measured optical rotatory dispersion of dimers. Contrary to previous studies, agreement is found not at all satisfactory. However, optical rotatory dispersion of 3′-5′-GpGpGpC and GpGpGpU can be estimated from the semiempirical expression, if a next-nearest interaction parameter is introduced empirically. Such interaction parameter can be calculated from the measured properties of trinucleotide sequences like GpGpG, GpGpC, and GpGpU, assuming that only the nearest-neighbor interaction is important. The optical rotatory dispersion of single-stranded poly(G) is also predicted. The importance of syn-anti equilibrium and next-nearest-neighbor interaction in oligoguanylic acids is suggested as a probable explanation.

Optical properties of magnetic crystals

From symmetry considerations and using generalized Onsager relations, it is shown that 66 of the 90 magnetic classes, consisting of 29 single colour and 37 double colour ones, can exhibit what may be called the strain gyrotropic rotation. Similarly, 69 of the 90 magnetic classes, consisting of 21 single colour and 48 double colour ones, can exhibit what may be called the strain gyrotropic birefringence. A crystal in the class m3 or m3 m is interesting as it can exhibit strain gyrotropic rotation despite its being cubic and incapable of exhibiting gyrotropic rotation in the unstressed state. Similarly, a crystal in the class m3 m, is interesting as it can exhibit strain gyrotropic birefringence despite its being cubic and incapable of exhibiting gyrotropic birefringence in the unstressed state.

Micellar size and shape in solutions of calcium stearate in cetane from optical depolarization data

Observations at a series of temperatures of the changes in viscosities and depolarization factors of 1% and 18% solutions of calcium stearate in cetane to which varying amounts of water have been added can be interpreted in terms of the existence of anisometric micelles. In general, changes in the size of the micelles inferred from values of ρh agree with those deduced from the viscosity data. The correlation between anisometry of micelles from rheological and optical observations is much poorer in the case of ρν, presumably because of the difficulty in differentiating the contribution of anisometry and anisotropy to ρν.

Simplified optical system for holographic subtraction

Subtraction of one complex spatial function from another can be accomplished holographically by shifting the phase of the reference beam by pi between the two exposures. A simple and reliable system for this purpose, which makes use of the fact that the beam from a gas laser is usually plane-polarized, is described, and its application to obtain the equivalent of a dark field with the frozen-fringe technique in holographic interferometry is demonstrated.

Sol-Gel Synthesis, characterization and optical properties of Tio2 thin films deposited on ITO/Glass substrates

TiO2 thin films have been deposited on glass and indium tin oxide (ITO) coated glass substrates by sol-gel technique. the influence of annealing temperature on the structural , morphological and optical properties has been examined. X-ray diffraction (XRD) results reveal the amorphous nature of the as-deposited film whereas the annealed films are found to be in the crystalline anatase phase. The surface morphology of the films at different annealing temperatures has been examined by atomic force microscopy (AFM). The in situ surface morphology of the as-deposited and annealed TiO2 films has also been examined by optical polaromicrograph (OPM). TiO2 films infatuated different structural and surface features with variation of annealing temperature. The optical studies on these films suggest their possible usage in sun-shielding applications.