Photoabsorption of attosecond XUV light pulses by two strongly laser-coupled autoionizing states

Abstract

We study theoretically the photoabsorption spectra of an attosecond XUV pulse by a laserdressed atomic system. A weak XUV excites an autoionizing state which is strongly coupled to another autoionizing state by a laser. The theory was applied to explain two recent experiments [Loh, Greene, and Leone, Chem. Phys. 350, 7 (2008); Wang, Chini, Chen, Zhang, Cheng, He, Cheng, Wu, Thumm, and Chang, Phys. Rev. Lett. 105 143002 (2010)] where the absorption spectra of the XUV lights were measured against the time delay between the laser and the XUV. In another example, we study an attosecond pulse exciting the 2s2p( 1 P ) resonance of helium which is resonantly coupled to the 2s 2 ( 1 S) resonance by a moderately intense 540 nm laser. The relation between the photoabsorption spectra and the photoelectron spectra and the modification of the transmitted lights in such an experiment are analyzed. The role of Rabi flopping between the two autoionizing states within their lifetimes is investigated with respect to the laser intensity and detuning.

Real-Time Probing of Electron Dynamics Using Attosecond Time-Resolved Spectroscopy

“…Intense few-cycle near-infrared pulses, commonly used in attosecond measurements, impart strong fields to the system and require the inclusion of higher-order response functions. The approach to model these experiments is to first calculate the single atom response (85,86) and then use various methods to scale this response up to a macroscopic system and include propagation effects (82,87). This approach treats all nonlinearities in one calculation (85).…”

“…Theoretical efforts have been crucial to understanding the intense few-cycle pulse interaction with atoms and the resulting quantum pathways that underlie the spectral features measured by an attosecond XUV pulse (7,86,93,94). The near-infrared pulses in these experiments also cause a phase shift in the induced dipole moment, resulting in changes to the lineshape of the transmitted XUV spectrum from Lorentzian to Fano (9,95).…”

Light-induced states in attosecond transient absorption spectra of laser-dressed helium

“…Attosecond transient absorption spectroscopy provides numerous opportunities for the design of experiments that take advantage of the complex interactions between an isolated attosecond pulse (IAP), a strong laser field, and a target medium [1][2][3][4]. Of particular interest are nonlinear processes that combine the IAP and laser fields.…”

Resolving intra-atomic electron dynamics with attosecond transient absorption spectroscopy

“…In a similar system, the dynamical control of XUV absorption and emission through the laser-induced coupling of the 2p and 2s was treated theoretically [23]. Laser-induced transparency at XUV photon energies in helium was also found for 800 nm dressing of the 2s2p( 1 P o ), 2p 2 ( 1 S e ) and 2s 2 ( 1 S) autoionising states [24,25].…”