Enhancing and controlling single-atom high-harmonic generation spectra: a time-dependent density-functional scheme

European Physical Journal B 88, (2015)

Enhancing and controlling single-atom high-harmonic generation spectra: a time-dependent density-functional scheme

Alberto Castro,Angel Rubio, E.K.U. Gross

High harmonic generation (HHG) provides a exible framework for the development of coherent light sources in the extreme-ultraviolet and soft x-ray regimes. However it su ers from low conversion eciencies as the control of the HHG spectral and temporal characteristics requires manipulating electron trajectories on attosecond time scale. The phase matching mechanism has been employed to selectively enhance speci c quantum paths leading to HHG. A few important fundamental questions remain open, among those how much of the enhancement can be achieved by the single-emitter and what is the role of correlations (or the electronic structure) in the selectivity and control of HHG generation. Here we address those questions by examining computationally the possibility of optimizing the HHG spectrum of isolated Hydrogen and Helium atoms by shaping the slowly varying envelope of a 800 nm, 200-cycles long laser pulse. The spectra are computed with a fully quantum mechanical description, by explicitly computing the time-dependent dipole moment of the systems using a rst-principles time-dependent density-functional approach (exact for the case of H). The sought optimization corresponds to the selective enhancement of single harmonics, which we nd to be signi cant. This selectivity is entirely due to the single atom response, and not due to any propagation or phase-matching e ect. In fact, this single-emitter enhancement adds to the phase-matching techniques to achieving even larger HHG enhancement factors. Moreover, we see that the electronic correlation plays a role in the determining the degree of optimization that can be obtained.

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arxiv
http://arxiv.org/abs/1409.4070
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This work was supported by the European Commission within the FP7 CRONOS project (ID 280879). AC acknowledges support by the University of Zaragoza through the project UZ2012-CIE-06. AR acknowledges nancial support from the European Research Council Advanced Grant DYNamo (ERC-2010-AdG-267374), Spanish Grant (FIS2010-21282-C02-01), and Grupos Consolidados UPV/EHU del Gobierno Vasco (IT578-13).

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