Coherent-Path Model for Nuclear Resonant Scattering of Gamma Radiation From Nuclei Excited by Synchrotron Radiation

Previous theoretical descriptions of nuclear resonant scattering of synchrotron radiation have been based on the semiclassical optical model or on several quantum mechanical models. These models are fine but do not give a clear physical picture of all the processes. The theory presented here gives a clear physical picture of all the relevant aspects of nuclear resonant scattering. The model treats the nuclear resonant sample as a one-dimensional chain of effective nuclei. However, the model is deceptive. It only appears to be one dimensional. It actually treats the sample as a series of effective planes. The analysis uses the time-dependent quantum mechanical techniques due to Heitler. A closed form solution, for the time-dependent forward scattered intensity, is found. The only parameter in the theory is N the number of effective nuclei (planes) in the model. It is shown that the prominent experimental features, the speed-up and dynamical beat effects, are primarily due to a π phase change of reemitted radiation. compared to the incident radiation, that occurs when radiation is absorbed and reemitted without recoil by a single \u27\u27effective nucleus (plane). The model also predicts results for the incoherent processes

The excitation of the spin coherence in ruby by the bichromatic laser field

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Inversionless amplification and propagation in an electronuclear level-mixing scheme

We study the propagation of a drive and probe bichromatic field in a compound electronuclear system [Opt. Commun. 179, 525 (2000)] from the viewpoint of inversionless amplification. In the regimes of adiabatic pulse and steady-state propagation, part of the ground-state population is trapped in a dark state thereby reducing the absorption of a probe field. This is reinforced by spontaneous emission for the steady-state case, for which the optimal amplification length is calculated. Beyond this length, the medium becomes absorbent for the probe field. In the complementary limit of ultrashort pulses, the medium reduces to a V scheme in which the drive field can self-induce transparency. © 2001 The American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Gain without inversion for gamma radiation

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Détermination par effet Mössbauer du coefficient de «self-diffusion» dans une vermiculite. Premiers résultats

The self-diffusion coefficient of exchangeable iron of vermiculite has bem determined by Mössbauer spectrometry using 57Co (vermiculite) as source. The obtained value (4.1-8 cm2 sec-1) has been compared to values determined by other authors for exchangeable sodium and potassium iom in the same mineral using radioactive tracer techniques.Le coefficient de «self-diffusion» d'ions de fer échangeable de la vermiculite a été déterminé par spectrométrie Mössbauer , utilisant 57Co (vermiculite ) comme source. La valeur obtenue de 4.1-8 cm2 sec-1 est comparée aux coefficients déterminés par d'autres auteurs dans le même minéral pour le sodium et le potassium échangeable.Helsen J., Schmidt K., Chakupurakal Th., Coussement R., Langouche G. Détermination par effet Mössbauer du coefficient de «self-diffusion» dans une vermiculite. Premiers résultats. In: Bulletin du Groupe français des argiles. Tome 24, fascicule 2, 1972. pp. 165-170

Population trapping in ruby

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Dark state in ruby: Analysis of the feasibility

Bichromatic excitation of the [Formula Presented] line in ruby at liquid-helium temperature is considered. The frequency difference of the spectral components of the driving field is resonant with the energy gap between the anticrossed spin sublevels [Formula Presented] and [Formula Presented] in the ground state [Formula Presented] The condition of the spin coherence trapping in the nonabsorbing state is analyzed. Population trapping is revealed in the reduced spontaneous emission from the excited state and in large spin magnetization of the ground state [Formula Presented] precessing with the frequency difference of the spectral components of the driving field. This magnetization can be detected by a pickup coil. The lifetime of the induced magnetization is strongly dependent on the ratio of the lifetime of the excited state [Formula Presented] and the spin coherence decay time [Formula Presented] © 2000 The American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe