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Atoms, Volume 3, Issue 4 (December 2015) – 2 articles , Pages 474-508

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497 KiB  
Article
Two-Photon Collective Atomic Recoil Lasing
by James A. McKelvie and Gordon R.M. Robb
Atoms 2015, 3(4), 495-508; https://doi.org/10.3390/atoms3040495 - 20 Nov 2015
Viewed by 4070
Abstract
We present a theoretical study of the interaction between light and a cold gasof three-level, ladder configuration atoms close to two-photon resonance. In particular, weinvestigate the existence of collective atomic recoil lasing (CARL) instabilities in differentregimes of internal atomic excitation and compare to [...] Read more.
We present a theoretical study of the interaction between light and a cold gasof three-level, ladder configuration atoms close to two-photon resonance. In particular, weinvestigate the existence of collective atomic recoil lasing (CARL) instabilities in differentregimes of internal atomic excitation and compare to previous studies of the CARL instabilityinvolving two-level atoms. In the case of two-level atoms, the CARL instability is quenchedat high pump rates with significant atomic excitation by saturation of the (one-photon)coherence, which produces the optical forces responsible for the instability and rapid heatingdue to high spontaneous emission rates. We show that in the two-photon CARL schemestudied here involving three-level atoms, CARL instabilities can survive at high pump rateswhen the atoms have significant excitation, due to the contributions to the optical forces frommultiple coherences and the reduction of spontaneous emission due to transitions betweenthe populated states being dipole forbidden. This two-photon CARL scheme may form thebasis of methods to increase the effective nonlinear optical response of cold atomic gases. Full article
(This article belongs to the Special Issue Cavity Quantum Electrodynamics with Ultracold Atoms)
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672 KiB  
Article
Electron Impact Excitation and Dielectronic Recombination of Highly Charged Tungsten Ions
by Zhongwen Wu, Yanbiao Fu, Xiaoyun Ma, Maijuan Li, Luyou Xie, Jun Jiang and Chenzhong Dong
Atoms 2015, 3(4), 474-494; https://doi.org/10.3390/atoms3040474 - 20 Nov 2015
Cited by 22 | Viewed by 5866
Abstract
Electron impact excitation (EIE) and dielectronic recombination (DR) of tungsten ions are basic atomic processes in nuclear fusion plasmas of the International Thermonuclear Experimental Reactor (ITER) tokamak. Detailed investigation of such processes is essential for modeling and diagnosing future fusion experiments performed on [...] Read more.
Electron impact excitation (EIE) and dielectronic recombination (DR) of tungsten ions are basic atomic processes in nuclear fusion plasmas of the International Thermonuclear Experimental Reactor (ITER) tokamak. Detailed investigation of such processes is essential for modeling and diagnosing future fusion experiments performed on the ITER. In the present work, we studied total and partial electron-impact excitation (EIE) and DR cross-sections of highly charged tungsten ions by using the multiconfiguration Dirac–Fock method. The degrees of linear polarization of the subsequent X-ray emissions from unequally-populated magnetic sub-levels of these ions were estimated. It is found that the degrees of linear polarization of the same transition lines, but populated respectively by the EIE and DR processes, are very different, which makes diagnosis of the formation mechanism of X-ray emissions possible. In addition, with the help of the flexible atomic code on the basis of the relativistic configuration interaction method, DR rate coefficients of highly charged W37+ to W46+ ions are also studied, because of the importance in the ionization equilibrium of tungsten plasmas under running conditions of the ITER. Full article
(This article belongs to the Special Issue Atomic Data for Tungsten)
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