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[en] In the present work, the coatings which contain different concentrations aluminum oxide (Al2O3) and boron carbide (B4C) on stainless steel 321 are produced by APS (Air Plasma Spray) method in order to investigate the surface morphologies and Raman effects of samples after 167 MeV energies and ions flux Φ=10''14 ions/cm''-2 ·sec Xe ion irradiation. The results showed that there were no morphological changes in the studied samples. On the other hand, it was observed some degenerations in the Raman spectrum analysis. It was carried out a comparative analysis of crystal structure of (Ss grade 321, B4C, Al2O3) compounds after heavy ions irradiation. The results revealed that Raman duplicates depend on the concentration of B4C/Al2O3 on 321 stainless steel.
[en] This tutorial review discusses some of the work that preceded development, twenty-five years ago, of the stimulated Raman adiabatic passage (STIRAP) technique, now widely used in the controlled coherent dynamics of three-state systems, noting how the use of time-dependent adiabatically-evolving population-trapping dark states made possible the robust and highly-efficient population transfer between quantum states that first popularized STIRAP. Preceding the history discussion is a tutorial definition of STIRAP and its necessary and sufficient ingredients — understanding that has led to applications well beyond those of the original quantum systems. This review also discusses the relationship between STIRAP and two related procedures: chirped Raman adiabatic passage (RCAP or CHIRAP) and electromagnetically induced transparency (EIT) with slow and captured light. It concludes with a brief discussion of ways in which contemporary STIRAP has extended the original concept and enlarged the definition, beyond that of simple quantum systems to classical macroscopic devices. Appendices offer further details. The presentation emphasizes theory but with illustrations of experimental results. (author)
[en] Raman amplification in plasma has been proposed to be a promising method of amplifying short radiation pulses. Here, we investigate chirped pulse Raman amplification (CPRA) where the pump pulse is chirped and leads to spatiotemporal distributed gain, which exhibits superradiant scaling in the linear regime, usually associated with the nonlinear pump depletion and Compton amplification regimes. CPRA has the potential to serve as a high-efficiency high-fidelity amplifier/compressor stage.
[en] A new formalism will be proposed for the Raman scattering from He II near the two-roton threshold. By showing that the processes including long wave-length photons in the intermediate states are enhanced it is found that the Raman intensity is proportional to the multi-phonon part of the structure factor. To study the structure factor the atomic density fluctuation is expanded in terms of the phonon-roton operators. Based on it the Hamiltonian for the elementary excitations is constructed. Then the structure factor is shown proportional to the generalized density of states of interacting rotons (GDOSIR): It contains the form-factor of a roton-pair creation from the atomic density at every vertex of ladder processes as well as at the places where the pair is created and annihilated by light quanta. Thanks to the commitment of long wave-length photons the proposed formalism is automatically free from the hard-core problem, with which the conventional ones should inevitably confront but were unable to cope
[en] Based on the new formalism which is developed elsewhere by one of the authors, and is free from the difficulty with which the conventional theories could not cope, the authors shall examine experimental Raman spectra of He II near the two-roton threshold. The intensity spectrum is determined by the generalized density of states of interacting rotons (GDOSIR). For the form factor of a roton-pair creation from the atomic density fluctuation which appears in GDOSIR, a power law in total energy is assumed. After investigating what types of characteristic structures and how they appear in GDOSIR as α, the power of the form factor, and g, the coupling constant, change, the authors shall perform line shape analysis between theory and experiment by varying g and δR, the roton-minimum energy, by including the instrumental width. It is found that α in the margin 0 ≤ α approx-lt 1/2 well reproduces experiments at SVP, 5, 10, 15 and 20 kg/cm2, the margin including that set by the direct roton-roton scattering experiment, namely α ∼ 1/2. Further it also includes the conventional theories as a special case (α=0), thereby solving the puzzle that the theories in error could have predicted the Raman feature so successfully. In addition the values of the coupling constant obtained by the Raman data here are in remarkable correspondence with those determined by the roton-roton scattering, thereby suggesting a possibility for the form of the interaction with α ∼ 1/2 to lead to a unified understanding of roton dynamics. Further the results for δR are not only in close agreement with each other for α in the Raman margin but also with the neutron results, from SVP to 20 kg/cm2. Therefore the Raman data alone can afford reliable information on the fundamental parameter of elementary excitations in He II
[en] Elevated metallic nanostructures with nanogaps (<10 nm) possess advantages for surface enhanced Raman scattering (SERS) via the synergic effects of nanogaps and efficient decoupling from the substrate through an elevated three-dimensional (3D) design. In this work, we demonstrate a pattern-transfer-free process to reliably define elevated nanometer-separated mushroom-shaped dimers directly from 3D resist patterns based on the gap-narrowing effect during the metallic film deposition. By controlling the initial size of nanogaps in resist structures and the following deposited film thickness, metallic nanogaps could be tuned at the sub-10 nm scale with single-digit nanometer precision. Both experimental and simulated results revealed that gold dimer on mushroom-shaped pillars have the capability to achieve higher SERS enhancement factor comparing to those plasmonic dimers on cylindrical pillars or on a common SiO2/Si substrate, implying that the nanometer-gapped elevated dimer is an ideal platform to achieve the highest possible field enhancement for various plasmonic applications. (paper)
[en] Spontaneous Raman processes in cold atoms have been widely used in the past decade for generating single photons. Here, we present a method to optimise their efficiencies for given atomic coherences and optical depths. We give a simple and complete recipe that can be used in present-day experiments, attaining near-optimal single photon emission. (paper)