Absolute frequency measurement of rubidium 5S-7S two-photon transitions with a femtosecond laser comb

The absolute frequencies of rubidium 5S-7S two-photon transitions at 760 nm are measured to an accuracy of 20 kHz with an optical frequency comb based on a mode-locked femtosecond Ti:sapphire laser. The rubidium 5S-7S two-photon transitions are potential candidates for frequency standards and serve as important optical frequency standards for telecommunication applications. The accuracy of the hyperfine constant of the 7S1/2 state is improved by a factor of 5 in comparison with previous results.     

The emission wavelength tuning of InAs/InP quantum dots with thin GaAs, InGaAs, InP capping layers by MOCVD

InAs quantum dots (QDs) were grown on InP substrates by metalorganic chemical vapor deposition. The width and height of the dots were 50 and 5.8 nm, respectively on the average and an areal density of 3.0×10¹⁰ cm⁻² was observed by atomic force microscopy before the capping process. The influences of GaAs, In_0.53Ga_0.47As, and InP capping layers (5–10 ML thickness) on the InAs/InP QDs were studied. Insertion of a thin GaAs capping layer on the QDs led to a blue shift of up to 146 meV of the photoluminescence (PL) peak and an InGaAs capping layer on the QDs led to a red shift of 64 meV relative to the case when a conventional InP capping layer was used. We were able to tune the emission wavelength of the InAs QDs from 1.43 to 1.89 μm by using the GaAs and InGaAs capping layers. In addition, the full-width at half-maximum of the PL peak decreased from 79 to 26 meV by inserting a 7.5 ML GaAs layer. It is believed that this technique is useful in tailoring the optical properties of the InAs QDs at mid-infrared regime.     

Correlation between Al2O3 particles and interface of Al-Al2O3 coatings by cold spray

Al-Al₂O₃ composite coatings with different Al₂O₃ particle shapes were prepared on Si and Al substrate by cold spray. The powder compositions of metal (Al) and ceramic (Al₂O₃) having different sizes and agglomerations were varied into ratios of 10:1 wt% and 1:1 wt%. Al₂O₃ particles were successfully incorporated into the soft metal matrix of Al. It was found that crater formation between the coatings and substrate, which is typical characteristic signature of cold spray could be affected by initial starting Al₂O₃ particles. In addition, when the large hard particles of fused Al₂O₃ were employed, the deep and big craters were generated at the interface between coatings and hard substrates. In the case of pure soft metal coating such as Al on hard substrate, it is very hard to get proper adhesion due to lack of crater formation. Therefore, the composite coating would have certain advantages.     

Measurement of the lifetime difference in the B0(s) system

We present a study of the decay B0(s) --> J/psiphi. We obtain the CP-odd fraction in the final state at time zero, Rperpendicular = 0.16 +/- 0.10(stat) +/- 0.02 (syst), the average lifetime of the (B0(s), B0(s)) system, tau(B0(s)) = 1.39(+0.13)(-0.16)(stat)(+0.01)(-0.02)(syst) ps, and the relative width difference between the heavy and light mass eigenstates, DeltaGamma/Gamma tripple bond (GammaL - GammaH)/Gamma = 0.24(+0.28)(-0.38)(stat)(+0.03)(-0.04)(syst). With the additional constraint from the world average of the lifetime measurements using semileptonic decays, we find tau(B0(s)) = 1.39 +/- 0.06 ps and DeltaGamma/Gamma = 0.25(+0.14)(-0.15). For the ratio of the B0(s) and B0 lifetimes we obtain tau(B0(s))/tau(B0) = 0.91 +/- 0.09(stat) +/- 0.003(syst).     

Search for supersymmetry via associated production of charginos and neutralinos in final states with three leptons

A search for associated production of charginos and neutralinos is performed using data recorded with the D0 detector at a pp center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider. This analysis considers final states with missing transverse energy and three charged leptons, of which at least two are electrons or muons. No evidence for supersymmetry is found in a data set corresponding to an integrated luminosity of 320 pb-1. Limits on the product of the production cross section and leptonic branching fraction are set. For the minimal supergravity model, a chargino lower mass limit of 117 GeV at the 95% C.L. is derived in regions of parameter space with enhanced leptonic branching fractions.     

Measurement of the Lambda0b lifetime in the decay lambda0b--> J/psiLambda0 with the D0 detector

We present measurements of the Lambda(0)(b) lifetime in the exclusive decay channel Lambda(0)(b)--> J/psiLambda(0), with J/psi--> mu(+)mu(-) and Lambda(0)--> ppi(-), the B0 lifetime in the decay B0-->J/psiK(0)(S) with J/psi--> mu(+)mu(-) and K(0)(S)-->pi(+)pi(-), and the ratio of these lifetimes. The analysis is based on approximately 250 pb(-1) of data recorded with the D0 detector in pp collisions at sqrt[s] = 1.96 TeV. The Lambda(0)(b) lifetime is determined to be tau(Lambda(0)(b)) = 1.22(+0.22)(-0.18)(stat) +/- 0.04(syst) ps, the B0 lifetime tau(B0) = 1.40(+0.11)(-0.10)(stat) +/- 0.03(syst) ps, and the ratio tau(Lambda(0)(b))/tau(B0) = 0.87(+0.17)(-0.14)(stat) +/- 0.03(syst). In contrast with previous measurements using semileptonic decays, this is the first determination of the Lambda(0)(b) lifetime based on a fully reconstructed decay channel.     

Influence of pretreatment methods on adsorption and catalytic characteristics of toluene over heterogeneous palladium based catalysts

The adsorption and catalytic characteristics of heterogeneous palladium based catalyst and its modified catalysts with gases (air and hydrogen) and acidic aqueous solution (HCl) were studied for evaluating the influence of pretreatment methods for toluene. The structural and energetic adsorption properties of the parent and pretreated catalysts were analyzed by means of nitrogen adsorption isotherms and gravimetric methods. The light-off curve and the XPS investigation were used for analyzing the catalytic activity and the surface state of palladium. It was clearly shown from the experimental results that hydrogen pretreated catalysts having metallic surface state exhibited the highest adsorption capacity and catalytic activity compared to that of parent and modified catalysts. The adsorption equilibrium data for toluene were obtained at three different temperatures and correlated successfully with the two-site Langmuir molecular isotherm model (L2m). It was also found that the palladium phase has more adsorption affinity for toluene molecules than the alumina support. The isosteric heat of adsorption calculated by using the Clausius-Clapeyron equation significantly changed with the coverage and the lateral interactions between the adsorbate-adsorbate molecules control the system. Furthermore, comparative analysis of the adsorption energy distribution revealed that the parent and its modified catalysts have different types of surface energetic heterogeneities.     

1.6 μm band double pass fiber Raman amplifiers using Raman fiber oscillator

We propose double pass fiber Raman amplifier schemes based on Raman fiber oscillator in order to amplify optical signal with wavelengths from 1610 to 1650 nm efficiently. We experimentally demonstrate that the proposed double pass amplifier scheme has enhanced gain characteristics compared to a conventional single pass scheme. We also demonstrate a scheme for the proposed double pass amplifier to have small gain variation over the wavelength range by using two fiber Bragg gratings with different center wavelengths.     

Control of resonant peak depths of tunable long-period fiber gratings using overcoupling

We present a method to reduce changes in the resonant peak depth of a long-period fiber grating (LPFG) as the resonant band is tuned by varying the external refractive index. We theoretically analyze the effects of the initial coupling strength on the peak depth change as external refractive index is varied. By controlling the initial coupling strength, it is experimentally demonstrated that an optimum peak depth can be obtained over a range of operating wavelengths that will maximize the sensitivity and stability of LPFG based sensors and tunable filters.     

Enhanced coercivity in sponge magnets with three dimensionally ordered nanopores

Nanoporous magnets are new promising materials particularly useful in biological assays and ion separations. This letter deals with a simple method for making porous magnets composed of cobalt ferrite, where polymer colloidal spheres were used as sacrificial templates. Compared with the bulk congener the porous cobalt ferrite shows enhancements in coercive field and magnetization, which could be associated with the presence of nanopores ordered three dimensionally. Using the sponge magnet complete removal of magnetic Cu and Fe ions was achieved while partial removal was observed with porous silicate having the same size of nanopores.