Synthesis of wurtzite-phase ZnS nanocrystal and its optical properties

The wurtzite phase of ZnS nanocrystal has been prepared by annealing in 200-600 degrees C temperature range, its cubic phase of 2-3 nm size. prepared through soft chemical method. Results of isochronal experiments of 2 h at different temperatures indicate that visible transformation to wurtzite from cubic ZnS appears at a temperature of 400 degrees C, which is about three times smaller than that of bulk ZnS phase transition temperature. The phases, nanostructures, and optical absorption characteristics are obtained through X-ray diffraction. transmission electron microscopy, and UV-visible absorption spectroscopy. A stable and green photoluminescence emission peaked at 518 nm is observed from the 600 degrees C annealed samples, under ultraviolet light excitation.

New light on the optical equivalence theorem and a new type of discrete diagonal coherent state representation

In many instances we find it advantageous to display a quantum optical density matrix as a generalized statistical ensemble of coherent wave fields. The weight functions involved in these constructions turn out to belong to a family of distributions, not always smooth functions. In this paper we investigate this question anew and show how it is related to the problem of expanding an arbitrary state in terms of an overcomplete subfamily of the overcomplete set of coherent states. This provides a relatively transparent derivation of the optical equivalence theorem. An interesting by-product is the discovery of a new class of discrete diagonal representations.

Self-image (autoidolon) techniques for the realisation of optical computing type operations

Abstract is not available.

Dielectric properties of Li2O-3B(2)O(3) glasses

The frequency and temperature dependences of the dielectric constant and the electrical conductivity of the transparent glasses in the composition Li2O-3B(2)O(3) were investigated in the 100 Hz-10 MHz frequency range. The dielectric constant and the loss in the low frequency regime were electrode material dependent. Dielectric and electrical relaxations were, respectively, analyzed using the Cole-Cole and electric modulus formalisms. The dielectric relaxation mechanism was discussed in the framework of electrode and charge carrier (hopping of the ions) related polarization using generalized Cole-Cole expression. The frequency dependent electrical conductivity was rationalized using Jonscher's power law. The activation energy associated with the dc conductivity was 0.80 +/- 0.02 eV, which was ascribed to the motion of Li+ ions in the glass matrix. The activation energy associated with dielectric relaxation was almost equal to that of the dc conductivity, indicating that the same species took part in both the processes. Temperature dependent behavior of the frequency exponent (n) suggested that the correlated barrier hopping model was the most apposite to rationalize the electrical transport phenomenon in Li2O-3B(2)O(3) glasses. These glasses on heating at 933 K/10 h resulted in the known nonlinear optical phase LiB3O5.

Diffusion of localized optical excitations and trap emission in ruby

Using the critical percolation conductance method the energy-dependent diffusion coefficient associated with thermally assisted transfer of the R1 line excitation between single Cr3+ ions with strain-induced randomness has been calculated in the 4A2 to E(2E) transition energies. For localized states sufficiently far away from the mobility edge the energy transfer is dominated by dipolar interactions, while very close to the mobility edge it is determined by short-range exchange interactions. Using the above energy-dependent diffusion coefficient a macroscopic diffusion equation is solved for the rate of light emission by Cr3+ ion-pair traps to which single-ion excitations are transferred. The dipolar mechanism leads to good agreement with recent measurements of the pair emission rate by Koo et al. (Phys. Rev. Lett., vol.35, p.1669 (1975)) right up to the mobility edge.

In situ pump probe optical absorption studies on Sb/As2S3 nanomultilayered film

We report the in situ optical transmission change in the complete visible region of the electromagnetic spectrum to asses the kinetics of photo induced interdiffusion in Sb/As2S3 nanomultilayered film. The interdiffusion of Sb into As2S3 matrix results in the formation of Sb-As2S3 ternary solid solutions which is explained by the change in optical band gap, absorption coefficients and Tauc parameter (B-1/2) with evolution of time. The wavelength dependence of the time constants provides a better description of photo induced effects. The time evolution of the absorption coefficients and optical band gap are significantly faster in this process. (C) 2009 Elsevier B.V. All rights reserved.

Stimulated interdiffusion and optical recording in Sb/As2S3 nanomultilayers

The role of the compositional modulation at nano-scale dimensions (similar to 2-10 nm) in the enhancement of optical recording parameters in nanomultilayers, which contain Sb as active, optical absorbing and diffusing layers and As2S3 as barrier (matrix) layers was investigated. Comparison was made with single homogeneous layers made of ternary (As2S3)(x)Sb1-x glasses and co-deposited from Sb and As2S3. It was shown that essential increase of the recording efficiency, sensitivity of the bleaching process, broadening of its spectral range occurs due to the stimulated interdiffusion of adjacent components in Sb/As2S3 nanomultilayers with optimized Sb layer thickness.

Glass transitions in arsenic-selenium glasses

Glaiis transitions of As-Se glasses have been investigated over a wide range of compositions by using differential scanning calorimetry. The variation of Tg with composition has been interpreted on the basis of a bond-lattice model.

Simplified theory of optical nonlinearities in spin-polarized semiconductors

The spin degree of freedom is largely disregarded in existing theories of the density-dependent optical properties of an interacting electron-hole plasma in quasiequilibrium. Here, we extended the pair equation, which is applicable to a bulk semiconductor at elevated temperatures, to calculate optical nonlinearities due to a spin-polarized plasma. We obtained agreement with recent circular dichroism data in laser-excited GaAs by using the plasma density alone as the fitting parameter. The simplicity of our theory, based on the analytical pair-equation formula, makes it ideal for conveniently modelling absorption in a carrier spin-polarized semiconductor.

Singular value decomposition based computationally efficient algorithm for rapid dynamic near-infrared diffuse optical tomography

Purpose: A computationally efficient algorithm (linear iterative type) based on singular value decomposition (SVD) of the Jacobian has been developed that can be used in rapid dynamic near-infrared (NIR) diffuse optical tomography. Methods: Numerical and experimental studies have been conducted to prove the computational efficacy of this SVD-based algorithm over conventional optical image reconstruction algorithms. Results: These studies indicate that the performance of linear iterative algorithms in terms of contrast recovery (quantitation of optical images) is better compared to nonlinear iterative (conventional) algorithms, provided the initial guess is close to the actual solution. The nonlinear algorithms can provide better quality images compared to the linear iterative type algorithms. Moreover, the analytical and numerical equivalence of the SVD-based algorithm to linear iterative algorithms was also established as a part of this work. It is also demonstrated that the SVD-based image reconstruction typically requires O(NN2) operations per iteration, as contrasted with linear and nonlinear iterative methods that, respectively, requir O(NN3) and O(NN6) operations, with ``NN'' being the number of unknown parameters in the optical image reconstruction procedure. Conclusions: This SVD-based computationally efficient algorithm can make the integration of image reconstruction procedure with the data acquisition feasible, in turn making the rapid dynamic NIR tomography viable in the clinic to continuously monitor hemodynamic changes in the tissue pathophysiology.

Optical tweezer for probing erythrocyte membrane deformability

We report that the average rotation speed of optically trapped crenated erythrocytes is direct signature of their membrane deformability. When placed in hypertonic buffer, discocytic erythrocytes are subjected to crenation. The deformation of cells brings in chirality and asymmetry in shape that makes them rotate under the scattering force of a linearly polarized optical trap. A change in the deformability of the erythrocytes, due to any internal or environmental factor, affects the rotation speed of the trapped crenated cells. Here we show how the increment in erythrocyte membrane rigidity with adsorption of Ca++ ions can be exhibited through this approach.

Automatic wildfire detection and simulation using optical information from unmanned aerial systems

In many parts of the world, uncontrolled fires in sparsely populated areas are a major concern as they can quickly grow into large and destructive conflagrations in short time spans. Detecting these fires has traditionally been a job for trained humans on the ground, or in the air. In many cases, these manned solutions are simply not able to survey the amount of area necessary to maintain sufficient vigilance and coverage. This paper investigates the use of unmanned aerial systems (UAS) for automated wildfire detection. The proposed system uses low-cost, consumer-grade electronics and sensors combined with various airframes to create a system suitable for automatic detection of wildfires. The system employs automatic image processing techniques to analyze captured images and autonomously detect fire-related features such as fire lines, burnt regions, and flammable material. This image recognition algorithm is designed to cope with environmental occlusions such as shadows, smoke and obstructions. Once the fire is identified and classified, it is used to initialize a spatial/temporal fire simulation. This simulation is based on occupancy maps whose fidelity can be varied to include stochastic elements, various types of vegetation, weather conditions, and unique terrain. The simulations can be used to predict the effects of optimized firefighting methods to prevent the future propagation of the fires and greatly reduce time to detection of wildfires, thereby greatly minimizing the ensuing damage. This paper also documents experimental flight tests using a SenseFly Swinglet UAS conducted in Brisbane, Australia as well as modifications for custom UAS.

The incongruous observation of magnetic phase separation in La0.85Sr0.15CoO3 spin glass system

Phase separation (PS) in hole-doped cobaltites (La1-xSrxCoxO3) is drawing renewed interest recently. In particular, the magnetic behavior of La0.85Sr0.15CoO3 has been subjected to a controversial debate for the past several years; while some groups show evidence for magnetic PS, others show spin glass (SG) behavior. Here, an attempt is made to resolve the controversy related to ``PS versus SG'' behavior in this compound. We present the results of a comprehensive investigation of the dc magnetization, ac susceptibility, and the magnetotransport properties of La0.85Sr0.15CoO3 samples. We contemplate that the magnetic PS in La0.85Sr0.15CoO3 is neither intrinsic nor inherent, but it is a consequence of the preparation conditions. It is realized that a low temperature annealed (LTA) sample shows PS whereas the high temperature annealed (HTA) sample shows SG behavior. The Brillouin-like behavior of field cooled dc magnetization and apparently no frequency dependent peak shift in ac susceptibility for the LTA sample characterize it to be of ferromagneticlike whereas a kink in field cooled dc magnetization and a considerable amount (similar to 3 K) of frequency dependent peak shift in the ac susceptibility for the HTA sample characterize it to be of SG state. The magnetotransport properties show that the HTA sample is more semiconducting as compared to the LTA sample. This is interpreted in terms of the presence of isolated as well as coalescing metallic ferromagnetic clusters in the case of LTA sample. The magnetoresistance (MR) at 10 K for the HTA sample exhibits a huge value (similar to 65%) as compared to the LTA sample, and it monotonically decreases with the rise in temperature. Such a high value of MR in the case of HTA sample is strongly believed to be due to the spin dependent part of random potential distribution. Further, the slow decay of remnant magnetization with progress of time and the existence of hysteresis at higher temperatures (up to 200 K) in the case of LTA sample as compared to the HTA sample clearly unveil different magnetic states associated with them.