Autoionization of argon atoms was studied experimentally by transient absorption spectroscopy with isolated attosecond pulses. The peak position, intensity, linewidth, and shape of the 3s3p 6 np 1 P Fano resonance series (26.6-29.2 eV) were modified by intense few-cycle near infrared laser pulses, while the delay between the attosecond pulse and the laser pulse was changed by a few femtoseconds. Numerical simulations revealed that the experimentally observed splitting of the 3s3p 6 4p 1 P line is caused by the coupling between two short-lived highly excited states in the strong laser field. DOI: 10.1103/PhysRevLett.105.143002 PACS numbers: 32.70.Jz, 32.80.Zb, 78.47.JÀ Bridging the gap between atomic physics and the complex systems that make up the world around us requires indepth study of electron correlation. While rotation and vibration of molecules can be studied by femtosecond lasers [1], observation of the electron-electron interaction requires attosecond time resolution [2]. One of the most interesting processes governed by electron-electron correlation is autoionization [3]. The Fano profile, which is the signature of the autoionization process, has widespread significance in many scientific disciplines [4][5][6][7]. For decades, spectral-domain measurements with synchrotron radiation have served as a window into the rich dynamics of autoionization [4]. However, the synchrotron pulse duration is too long (100 fs to 100 ps) to time-resolve the Fano resonances since the autoionization lifetimes can be as short as a few femtoseconds.Since the generation of the first isolated attosecond pulses in 2001 [8], it was theoretically proposed [9][10][11][12][13] and experimentally demonstrated [14] that time-resolved Fano profiles can be studied using the attosecond streaking technique. To date, most theoretical and experimental investigations of autoionization processes have scrutinized Fano profiles as a function of the photoelectron energy. However, made possible by significant recent progress in short-pulse laser technology [15], timeresolved transient XUV photoabsorption measurements have become feasible, which gives access to complimentary studies of atomic autoionization in the time regime [16,17]. Photoabsorption measurements typically have higher data collection efficiency and better energy resolution than what can be obtained by detecting photoelectrons. The setup is all-optical, much simpler than the attosecond streak camera. Here we demonstrate the first transient absorption experiment using isolated attosecond pulses to probe the autoionization of atoms and show that the autoionization process is strongly modified by an intense laser field.Fano resonance profiles in the absorption spectrum are the result of interference between the direct ionization and the decay from an autoionizing state due to configuration interaction [3]. It is characterized by the resonance energy E r , its width that is related to the lifetime of the autoionizing state by ¼ @=À, and the q parameter, which represents the ratio...

Two-color (800 and 400 nm) short (45 fs) linearly polarized pulses are used to ionize and dissociate D2 into a neutral deuterium atom and a deuteron. The yields and energies of the ions are measured left and right along the polarization vector. As the relative phase of the two colors is varied, strong yield asymmetries are found in the ion-energy regions traditionally identified as bond softening, above-threshold dissociation and rescattering. The asymmetries in these regions are quite different. A model based on the dynamic coupling by the laser field of the gerade and ungerade states in the molecular ion accounts for many of the observed features.

We study the control of dissociation of the hydrogen molecular ion and its isotopes exposed to two ultrashort laser pulses by solving the time-dependent Schrödinger equation. While the first ultraviolet pulse is used to excite the electron wave packet on the dissociative 2psigma{u} state, a second time-delayed near-infrared pulse steers the electron between the nuclei. Our results show that by adjusting the time delay between the pulses and the carrier-envelope phase of the near-infrared pulse, a high degree of control over the electron localization on one of the dissociating nuclei can be achieved (in about 85% of all fragmentation events). The results demonstrate that current (sub-)femtosecond technology can provide a control over both electron excitation and localization in the fragmentation of molecules.

We demonstrate an experimental control of electron localization in deuterium molecular ions created and dissociated by the combined action of an attosecond pulse train and a many-cycle infrared (IR) pulse. The attosecond pulse train is synthesized using both even and odd high order harmonics of the driving IR frequency so that it can strobe the IR field once per IR cycle. An asymmetric ejection of the deuterium ions oscillates with the full IR period when the APT-IR time-delay is scanned. The observed control is due to the creation of a coherent superposition of 1s sigma{g} and 2p sigma{u} states via interference between one-photon and two-photon dissociation channels.