Argon-photoion–Auger-electron Coincidence Measurements Following K-shell Excitation by Synchrotron Radiation

Argon photoion spectra have been obtained for the first time in coincidence with K-LL and K-LM Auger electrons, as a function of photon energy. The simplified charge distributions which result exhibit a much more pronounced photon-energy dependence than do the more complicated noncoincident spectra. In the near-K-threshold region, Rydberg shakeoff of np levels, populated by resonant excitation of K electrons, occurs with significant probability, as do double-Auger processes and recapture of the K photoelectron through postcollision interaction

Interchannel Coupling in the Photoionization of the M-shell of Kr Well Above Threshold: Experiment and Theory

Photoionization cross sections and asymmetry (β) parameters for Kr 3s, 3p, and 3d subshells have been measured and calculated in the 300–1300-eV photon energy range. Good agreement between experiment and theory is found for both cross-section branching ratios and β parameters. Interchannel coupling among the channels arising from 3s, 3p, and 3d subshells is found to be necessary for quantitative accuracy of the theory. This shows that the interchannel coupling phenomenology far above threshold, found previously for outer shells of Ne and Ar, is also operative for inner atomic shells

Gain without population inversion in V-type systems driven by a frequency-modulated field

We obtain gain of the probe field at multiple frequencies in a closed three-level V-type system using frequency modulated pump field. There is no associated population inversion among the atomic states of the probe transition. We describe both the steady-state and transient dynamics of this system. Under suitable conditions, the system exhibits large gain simultaneously at series of frequencies far removed from resonance. Moreover, the system can be tailored to exhibit multiple frequency regimes where the probe experiences anomalous dispersion accompanied by negligible gain-absorption over a large bandwidth, a desirable feature for obtaining superluminal propagation of pulses with negligible distortion.Comment: 10 pages + 8 figures; To appear in Physical Review

Lasing without inversion in three-level systems : self-pulsing in the cascade schemes

Lasing without inversion (LWI) in specific models of closed three-level systems is analyzed in terms of nonlinear dynamics. From a linear stability analysis of the trivial nonlasing solution of the homogeneously broadened systems with on-resonance driving and laser fields, we find that, near lasing threshold, resonant closed Λ and V schemes yield continuous-wave LWI while resonant cascade schemes can give rise to self-pulsing LWI. The origin of this different behavior is discussed. For parameters of a real cascade system in atomic 138Ba we check numerically that the self-pulsing solution is stable in a broad range of nonzero detunings. It is shown that the self-pulsing emission can still be observed when the typical residual Doppler broadening of an atomic beam is taken into account

Breakdown of the Independent Particle Approximation in High-Energy Photoionization

The independent particle approximation is shown to break down for the photoionization of both inner and outer nℓ (ℓ\u3e0) electrons of all atoms, at high enough energy, owing to interchannel interactions with the nearby ns photoionization channels. The effect is illustrated for Ne 2p in the 1 keV photon energy range through a comparison of theory and experiment. The implications for x-ray photoelectron spectroscopy of molecules and condensed matter are discussed

Post-Collision-Interaction Effects in HCl Following Photofragmentation Near the Chlorine K Edge

Ion time-of-flight mass spectroscopy was used to study the relaxation dynamics of HCl following photoexcitation in the vicinity of the Cl K threshold (~2.8 keV). Detailed observations of molecular fragmentation mediated by postcollision interaction between a photoelectron and an Auger electron are presented, evidenced by the recapture of Cl K photoelectrons by either Cln+ or H+ dissociation fragments. [S1050-2947(98)51206-1

Neutral Dissociation of Hydrogen Following Photoexcitation of HCl at the Chlorine K Edge

Time-of-flight mass spectroscopy was used to study the relaxation dynamics of HCl following photoexcitation in the vicinity of the Cl K edge (~2.8 keV) using monochromatic synchrotron radiation. At the lowest resonant excitation to the 6ơ* antibonding orbital, almost half of the excited molecules decay by emission of a neutral H atom, mostly in coincidence with a highly charged Cln1 ion. The present work demonstrates that neutral-atom emission can be a significant decay channel for excited states with very short lifetimes (1 fs). [S1050-2947(98)03604-X

Diagnosis for Education Maker Space for Sustainable Development with Emphasis on Polymeric Waste

Neste artigo são apresentadas atividades relacionadas ao projeto Espaço Maker de Educação para o Desenvolvimento Sustentável com Base no Design for Change. O objetivo está dirigido à educação para a sustentabilidade e à cultura maker, voltadas à problemática de resíduos poliméricos, a fim de difundir conceitos e a prática da sustentabilidade entre estudantes de escolas de ensino fundamental e médio. A metodologia consiste na revisão de literatura, levantamento de informações relacionadas a práticas educativas e ao processo de coleta e destinação dos resíduos. Foram realizadas visitas e diálogo com professores de uma escola de Joinville/SC, contato e levantamento de informações com a empresa responsável pela coleta seletiva de resíduos do município e visita em uma associação de catadores e recicladores. As informações obtidas contribuíram para a elaboração de um diagnóstico que servirá de base para aplicação do projeto nas escolas.This article presents activities related to the project entitled Maker Space of Education for Sustainable Development Based on Design for Change. The objective is aimed at education for sustainability and the maker culture, focused on the problem of polymeric waste, in order to disseminate concepts and the practice of sustainability among students from elementary and high schools. The methodology consists of reviewing the literature, gathering information related to educational practices and the process of collecting and disposing of waste. Visits and dialogue with teachers from a school in Joinville/SC, contact and information gathering with the company responsible for the selective collection of waste in the municipality, and visit to an association of collectors and recyclers were carried out. The information obtained contributed to the elaboration of a diagnosis that will serve as a basis for the application of the project in schools