title: Beyond the single-atom response in absorption line shapes: probing a dense, laser-dressed helium gas with attosecond pulse trains.
abstract: We investigate the absorption line shapes of laser-dressed atoms beyond the single-atom response, by using extreme ultraviolet (XUV) attosecond pulse trains to probe an optically thick helium target under the influence of a strong infrared (IR) field. We study the interplay between the IR-induced phase shift of the microscopic time-dependent dipole moment and the resonant-propagation-induced reshaping of the macroscopic XUV pulse. Our experimental and theoretical results show that as the optical depth increases, this interplay leads initially to a broadening of the IR-modified line shape, and subsequently, to the appearance of new, narrow features in the absorption line.
authors.affiliation: College of Optical Sciences and Department of Physics, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Chen-Ting
authors.initials: CT
authors.lastname: Liao
authors.affiliation: College of Optical Sciences and Department of Physics, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Arvinder
authors.initials: A
authors.lastname: Sandhu
authors.affiliation: Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
authors.forename: Seth
authors.initials: S
authors.lastname: Camp
authors.affiliation: Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Schafer
authors.affiliation: Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
authors.forename: Mette B
authors.initials: MB
authors.lastname: Gaarde
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry; D006371:Helium / Q000737:chemistry*; D053844:Lasers, Solid-State; D008962:Models, Theoretical; D013057:Spectrum Analysis / Q000379:methods; D014025:Titanium / Q000737:chemistry
chemical_list: D006371:Helium; D014025:Titanium; D000537:Aluminum Oxide