Monolithic integrated waveguide photodetector

An InGaAs photodetector for detection in the 1.0?1.5?m wavelength range has been integrated at the end of and above a ridge waveguide in InP. The waveguides were in n?-InP/n+-InP and had an average propagation loss of 3dB/cm at 1.15?m. The reflection losses were 3dB and the coupling loss was 2dB. The photodetector was an InGaAs photoconductor lattice-matched to InP and exhibited a bias-dependent optical gain of up to 2.5 with a unity-gain quantum efficiency of 49% at 1.15?m. 25% of the guided light was absorbed by the photoconductor. The speed of the photoconductor was found to be bias-dependent, varying from 10 ns to 150 ns rise/fall times.     

Regulation of Charge Carrier Dynamics in ZnO Microarchitecture‐Based UV/Visible Photodetector via Photonic‐Strain Induced Effects

A feasible, morphological influence on photoresponse behavior of ZnO microarchitectures such as microwire (MW), coral‐like microstrip (CMS), fibril‐like clustered microwire (F‐MW) grown by one‐step carrier gas/metal catalyst “free” vapor transport technique is reported. Among them, ZnO F‐MW exhibits higher photocurrent (I_Ph) response, i.e., I_{Ph/ZnO F‐MW} > I_{Ph/ZnO CMS} > I_{Ph/ZnO MW}. The unique structural alignment of ZnO F‐MW has enhanced the I_Ph from 14.2 to 186, 221, 290 µA upon various light intensities such as 0 to 6, 11, 17 mW cm^?2 at λ_{405 nm}. Herein, the nature of the as‐fabricated ZnO photodetector (PD) is also demonstrated modulated by tuning the inner crystals piezoelectric potential through the piezo‐phototronic effect. The I_Ph response of PD decreases monotonically by introducing compressive strain along the length of the device, which is due to the synergistic effect between the induced piezoelectric polarization and photogenerated charge carriers across the metal–semiconductor interface. The current behavior observed at the two interfaces acting as the source (S) and drain (D) is carefully investigated by analyzing the Schottky barrier heights (Φ_SB). This work can pave the way for the development of geometrically modified strain induced performances of PD to promote next generation self‐powered optoelectronic integrated devices and switches.     

Iron minerals and their influence on the optical properties of two Indian kaolins

Kaolin is mostly associated with minor quantities of ancillary minerals containing transition elements such as iron and titanium. These ions impart color to the white kaolin which adversely affects its application in paper and paint industries. Hence their removal is of prime importance in the optimum utilization of kaolin. The coloring effect as well as the mode of removal of these impurities depends on the “species” of the ion and/or the type of mineral. The present paper deals with the investigation on two Indian kaolins of different geological origin, one from Gujarat state at the western part of India and the other from Kerala State at the southern most part. Detailed physical, chemical and mineralogical characterization of the samples was carried out. The product clays after beneficiation by size classification, high gradient magnetic separation and chemical leaching were found to be of acceptable grade for paper industry with respect to optical properties and particle size. The impurity minerals were concentrated by different methods so that their identification was easier. Attempts were made to study the Fe species by correlating the XRD, chemical assay, DCB treatment and EPR spectral information of the clay samples before and after beneficiation. Iron stained anatase was found to be the major impurity in the Gujarat clay whereas iron was present as oxide/hydroxide in the Kerala sample. The beneficiated products from the Kerala clay were found to have better optical properties.     

Continuous wave cavity ring down spectroscopy measurements of velocity distribution functions of argon ions in a helicon plasma

We report continuous wave cavity ring down spectroscopy (CW-CRDS) measurements of ion velocity distribution functions (VDFs) in low pressure argon helicon plasma (magnetic field strength of 600 G, T(e) ≈ 4 eV and n ≈ 5 × 10(11) cm(-3)). Laser induced fluorescence (LIF) is routinely used to measure VDFs of argon ions, argon neutrals, helium neutrals, and xenon ions in helicon sources. Here, we describe a CW-CRDS diagnostic based on a narrow line width, tunable diode laser as an alternative technique to measure VDFs in similar regimes but where LIF is inapplicable. Being an ultra-sensitive, cavity enhanced absorption spectroscopic technique; CW-CRDS can also provide a direct quantitative measurement of the absolute metastable state density. The proof of principle CW-CRDS measurements presented here are of the Doppler broadened absorption spectrum of Ar II at 668.6138 nm. Extrapolating from these initial measurements, it is expected that this diagnostic is suitable for neutrals and ions in plasmas ranging in density from 1 × 10(9) cm(-3) to 1 × 10(13) cm(-3) and target species temperatures less than 20 eV.     

Optimization of hybrid laser–TIG welding of 316LN stainless steel using genetic algorithm

Determination of optimum hybrid laser–TIG welding process variables for achieving the maximum depth of penetration (DOP) in type 316LN stainless steel has been carried out using a genetic algorithm (GA). Nd:YAG pulsed laser and the TIG heat source were coupled at the weld pool to carry out hybrid welding. Design of experiments approach was used to generate the experimental design matrix. Bead-on-plate welds were carried out based on the design matrix. The input variables considered were laser power, pulse frequency, pulse duration, and TIG current. The response variable considered was the DOP. Multiple-regression model was developed correlating the process variables with the DOP using the generated data. The regression model was used for evaluating the objective function in GA. GA-based model was developed and it produced a set of solutions. Tournament and roulette wheel selection methods were used during the execution of GA. It was found that both the selection methods identified similar welding process parameters for achieving the maximum DOP. Excellent agreement was observed between the target DOP and the DOP values obtained in the validation experiments during hybrid laser–TIG welding.     

A multiscale model for quantifying helium diffusion in porous unsintered glass

Helium‐aided sintering of porous unsintered glass is a complex multiscale process, characterised by three different timescales, namely, that of helium diffusion, heat conduction, and radial shrinkage of the glass core. This work presents a multiscale model for quantifying heat and helium diffusion in a shrinking core system by decoupling the timescales based on their orders of magnitude. We obtain analytical solutions of our model, which allow us to quantify the spatio‐temporal profiles of temperature and helium concentration in the glass during the sintering process. Our results show that the introduction of helium increases the sintering rate of glass, and we conclude that pre‐sintering heating followed by helium‐aided sintering is better than simultaneous heating and helium diffusion. We also show that the pre‐sintering heating process for a standard glass sample should not be longer than an hour for the sake of heat economy, following which we may switch to the helium‐aided sintering process, where the sintering should occur under isothermal conditions for approximately 6 h. We perform dynamic simulations using glass porosity as a parameter, and find the sintering rate to be directly proportional to the initial porosity of the glass sample.     

Importance of Cr2O3 layer for growth of carbon nanotubes on superalloys

We present a detailed investigation of the formation of stable catalyst particles on Inconel substrates, an important step in the growth mechanism of carbon nanotubes on these substrates. The chemical nature of the interaction of catalyst and substrate was investigated using XPS, high-resolution cross-sectional TEM, and EDS studies. The results indicate that Cr₂O₃, an electrically conductive oxide, plays an important role in stabilizing nanoclusters of Fe catalyst under typical growth conditions. The nature of growth on a number of other superalloys is also presented and is examined with respect to their chemical composition.