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The effects of pre-plasmas on the electron beam directionality was experimentally and numerically investigated. Single material and layered targets made of Ti and/or CH were used to simultaneously measure high-energy (≥ 3 MeV) electrons along two directions, pre-pulse energy and pre-plasma density. The electron directionality is quantified by using a new parameter, the electron energy ratio of the total kinetic energies along the two directions. Measurements and radiation–hydrodynamic (RH) simulations show that a large (≥ 3.5 μ m) plasma scale length at the critical surface enhances electrons along the laser axis, and such pre-plasma conditions could only be achieved with the CH targets. Particle-in-cell simulations were performed on the RH generated pre-plasmas from Ti and CH targets, and the results show that the CH target provided conditions for higher forward momentum gains by electrons. First, the CH target allowed longer distances for electrons to interact with laser. Second, the intense laser pulse modified the critical surface, but the resulting surface differed. The CH target resulted in a smooth surface where a retro-reflection was observed while the Ti target resulted in a rippled surface that scattered the reflected light. As results, the CH electrons gained higher forward momentum via a direct-laser-acceleration in the counter propagating laser fields. The results presented in this article show a way of controlling the high-energy electron directionality. [ABSTRACT FROM AUTHOR]

The efficiencies of one- and two-photon absorption by chromophores in solution may be significantly modified by a sufficiently intense beam of off-resonant light. A molecular analysis based on quantum electrodynamics (QED) fully accounts for this phenomenon of laser-modified absorption. A time-dependent perturbation-theory treatment describes the process in terms of stimulated forward Rayleigh-scattering of the auxiliary beam occurring simultaneously with the absorption interaction( s). Our formulation accommodates media modifications to the basic character of light-matter interactions, taking into account the refractive and dispersive properties of a solution-phase environment. This introduces the bulk refractive index of the solvent directly into the QED framework. The measurable electronic response of molecules freely rotating in solution is defined by an average of all orientations. We explicitly derive fixed-orientation and rotationally averaged calculations for the Fermi-rule rate of laser-modified one- and two-photon absorption. For a given beam polarization geometry, the solution-phase molecular response is expressible as a set of natural invariant scalars. These results reveal details of the dependence on the beam polarisations and on the rotationally averaged molecular response: we illustrate the breadth of variation available via geometric manipulation of beam polarization, and raise new possibilities for quantum weak measurements of laser states. [ABSTRACT FROM AUTHOR]

Using nonlinear mathematical models and experimental data from laboratory and clinical studies, we have designed new combination therapies against COVID-19. [ABSTRACT FROM AUTHOR]

The optical emission from a pair of nanoantennas is investigated within the theoretical framework of quantum electrodynamics. The analysis of fluorescent emission from a pair of molecular antenna species in close proximity is prompted by experimental work on oriented semiconductor polymer nanostructures. Each physically different possibility for separation-dependent features in photon emission by any such pair is explored in detail, leading to the identification of three distinct mechanisms: emission from a pair-delocalized exciton state, emission that engages electrodynamic coupling through quantum interference, and correlated photon emission from the two components of the pair. Although each mechanism produces a damped oscillatory dependence on the pair separation, each of the corresponding results exhibits an analytically different form. Significant differences in the associated spatial frequencies enable an apparent ambiguity in the interpretation of experiments to be resolved. Other major differences are found in the requisite conditions, the associated selection rules, and the variation with angular disposition of the emitters, together offering grounds for experimental discrimination between the coupling mechanisms. The analysis paves the way for investigations of pair-wise coupling effects in the emission from nanoantenna arrays. [ABSTRACT FROM AUTHOR]

In the analysis of molecular structure and local order in heterogeneous samples, multiphoton excitation of fluorescence affords chemically specific information and high-resolution imaging. This report presents the results of an investigation that secures a detailed theoretical representation of the fluorescence polarization produced by one-, two-, and three-photon excitations, with orientational averaging procedures being deployed to deliver the fully disordered limits. The equations determining multiphoton fluorescence response prove to be expressible in a relatively simple, generic form, and graphs exhibit the functional form of the multiphoton fluorescence polarization. Amongst other features, the results lead to the identification of a condition under which the fluorescence produced through the concerted absorption of any number of photons becomes completely unpolarized. It is also shown that the angular variation of fluorescence intensities is reliable indicator of orientational disorder. [ABSTRACT FROM AUTHOR]

Deals with a study which demonstrated the use of an electrochemical cell as a source of chalcogem dimers for n-type doping of Ga[sub1-x]Al[subx]As films grown by molecular-beam epitaxy. Experimental details; Results; Discussion.

Presents a study which examined the adsorption of triethylgallium on the gallium arsenide surface. Experimental details; Results and discussion; Conclusion.

Investigates the sulphur doping behavior of gallium antimonide (GaSb) grown by molecular-beam epitaxy. Challenges in doping of MBE-grown GaSb; Methodology of the study; Discussion on the result of the study.

Normal incidence transmission measurements and surface plasmon spectroscopy at optical frequencies are used to probe the optical and structural properties of an optically nonlinear dye, deposited onto glass and silver substrates by the Langmuir–Blodgett technique. The particular orientation and proximity to the silver surface afforded by the deposition method reveals strong molecule/metal interactions hitherto unreported for LB film assemblies on silver. [ABSTRACT FROM AUTHOR]

Investigates the effect of source species, substrate temperature, substrate orientation, and group-V overpressure on the growth rate and composition of gallium arsenide (GaAs) and indium gallium arsenic (InGaAs) alloys grown by chemical beam epitaxy. GaAs growth rate against substrate temperature; GaAs partial growth rate in GaInAs alloys; GaAs partial growth rate.

The University of Rochester’s Laboratory for Laser Energetics (Rochester, New York) is leading an effort to develop a modern, fully automated streak camera. Characterization of a prototype camera shows spatial resolution better than 20 lp/mm, temporal resolution of 12 ps, line-spread function of 40 μm (full width at half maximum) contrast transfer ratio of 60% at 10 lp/mm, system gain of 101 charge-coupled device electrons per photoelectron, and a dynamic range of 500 for a 2 ns window. [ABSTRACT FROM AUTHOR]

Anomalous doping behavior of the most commonly used n-type dopants, Si and Sn, has been observed in InP grown by chemical beam epitaxy from trimethylindium and cracked phosphine. In the case of Si, although incorporation is initially facile, the doping level decreases in successive runs. It is proposed that this decrease is due to the formation of SiC in the dopant cell. The behavior of Sn is more complex. In the range of Sn cell temperatures from 600 to 750 °C, incorporation is proportional to the elemental Sn vapor pressure. However, at low cell temperatures, 175–350 °C, anomalously large incorporations of Sn are observed. We attribute this behavior to the formation of a volatile metalorganic precursor within the Sn cell, its transport to the substrate, and subsequent decomposition and incorporation. [ABSTRACT FROM AUTHOR]

We report the growth of nominally undoped InP by molecular beam epitaxy (MBE) from metallic indium, trimethylindium, or triethylindium and phosphine. We find significantly reduced acceptor incorporation when metalorganic sources are used, with exciton-dominated photoluminescence at 4.2 K and electron mobilities up to 47 500 cm2 V-1 s-1 at 77 K. The 4.2 K photoluminescence indicates that the residual shallow acceptors are either Ca, Mg, or Be. The carbon incorporation appears to be minimal. Interestingly, there is also little difference in electrical and optical properties of InP grown by metalorganic molecular beam epitaxy (MOMBE) using trimethyl or triethylindium, in marked contrast to the situation for GaAs MOMBE growth using trimethyl or triethylgallium. [ABSTRACT FROM AUTHOR]

The direct energy gap of thin, undoped epitaxial layers of Al1-xInxAs grown on (100) InP has been measured as a function of In content for values of x between 0.46 and 0.55 using catholuminescence spectroscopy. For the composition lattice matched to InP it was measured to be 1.450 eV at room temperature, and 1.508 eV at 4 K. Over the limited range of compositions studied, it varied as Eg =1.450+2.29 Δx eV at room temperature, and as Eg =1.508+2.22 Δx eV at 4 K, where Δx=(0.52-x), the deviation of x from the lattice-matched value. [ABSTRACT FROM AUTHOR]

Presents a correction to the article 'Irreducible Tensors and Selection Rules for Three-Frequency Absorption.'

Selective area growth of InP/InGaAs multiple quantum well laser structures has been demonstrated in openings defined in Si3 N4 layers on InP substrates. Growth was achieved, by metalorganic molecular beam epitaxy, in openings as small as 3 μm wide, but no growth occurred on the dielectric coating. Cathodoluminescence from individual laser stripes was observed at 300 K with a wavelength determined to be 1.57 μm and at 100 K with a wavelength of 1.46 μm. [ABSTRACT FROM AUTHOR]