Showing papers by "University of Massachusetts Boston published in 1972"
TL;DR: In this article, the rate of absorption of energy from a weak signal field by an atom driven by a strong pump field is evaluated, and the results are discussed in the context of a theorem which expresses the absorption line-shape function for general atomic systems in terms of a suitable atomic correlation function.
Abstract: The rate of absorption of energy from a weak signal field by an atom driven by a strong pump field is evaluated. The pump field and the signal field are assumed to induce transitions between the same pair of states, and their frequencies are both assumed to lie near the atomic resonance frequency for the transition in question. We find that the signal-field absorption line-shape function takes on negative values, representing stimulated emission rather than absorption, even though population inversion does not occur. This amplification of the signal field, which is most pronounced at high pump intensities, is shown to occur primarily at the expense of the pump field, which suffers an increased rate of attenuation. The results are discussed in the context of a theorem which expresses the absorption line-shape function for general atomic systems in terms of a suitable atomic correlation function.
448 citations
TL;DR: In this paper, the converse is shown to be true if U does not contain certain Type II 1 factors as direct summands, which is the case when U is abelian and weakly closed.
109 citations
TL;DR: In this article, the effect of pump field oscillations on the emission and absorption line-shape functions for an atom is discussed, where the pump field is assumed to oscillate at a frequency near the resonance frequency for transitions between a single pair of atomic states.
Abstract: The effect of a driving or pump field on the emission and absorption line-shape functions for an atom is discussed. The pump field is assumed to oscillate at a frequency near the resonance frequency for transitions between a single pair of atomic states, and transitions between one of these states and any other state of the atom are analyzed. The pump field is treated classically, and atomic relaxation is treated in general terms. The emission and absorption line-shape function (the latter is defined as the rate of absorption of energy from a weak signal field, applied in addition to the pump field, as a function of the signal-field frequency) are found by evaluating the relevant two-time atomic correlation functions in the Markoff approximation. In the limit of high pump-field intensity, both the absorption and the emission spectra are doubly peaked at frequencies which differ from the usual resonance frequency by $\ifmmode\pm\else\textpm\fi{}\frac{1}{2} \ensuremath{\Omega}$, where $\ensuremath{\Omega}$ is the frequency of the pump-field-induced oscillations in the populations of the two strongly coupled states. The absorption and the emission spectra are represented by essentially the same function in the limit of high pump-field intensity, as they are also in the limit of vanishing pump-field intensity. For intermediate pump-field intensities, however, the two functions are quite different in form, and no simple proportionality exists between them.
93 citations
60 citations
TL;DR: In this article, single crystals of Tl2CrO4 have been prepared by diffusion controlled slow growth in silica-gel medium and the crystal structure has been determined by a three-dimensional X-ray diffraction study.
15 citations
TL;DR: La structure génétique de 7 populations du gastéropode marinLittorina littorea a étudiée par analyse de phénotypes d'estérases révélés par électrophorèse sur gel de polyacrylamide.
Abstract: La structure genetique de 7 populations du gasteropode marinLittorina littorea a ete etudiee par analyse de phenotypes d'esterases reveles par electrophorese sur gel de polyacrylamide. Les populations des USA (Maine, Massachusetts), d'origine recente, ont davantage de variation geographique que celles de France, d'origine ancienne. De plus, parmi ces dernieres il y a reduction de l'heterozygotie dans l'echantillon semi-isole du Golfe du Morbihan.
11 citations
TL;DR: In this paper, a DWBA analysis of the data gives a value of the spectroscopic factor of 0.80 ± 0.03, in good agreement with the results of 40Ca(d, p0)41Ca, experiments.
11 citations
9 citations
TL;DR: Two programs which resolve an experimental envelope curve into its component overlapping peaks are offered, one of which fits symmetrical gaussian peaks and the other fits skewed or tailing peaks having the functional form of the Su frequency distribution.
4 citations
TL;DR: In this article, the structural impediments to change in the Qazvin bazaar are discussed, and the authors propose a method to overcome these impediments, which they call "structural impediments".
Abstract: (1972). Structural impediments to change in the Qazvin bazaar. Iranian Studies: Vol. 5, No. 4, pp. 130-148.
3 citations