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...

Photoionization by attosecond extreme ultraviolet (xuv) pulses into the laser-dressed continuum of the ionized atom is commonly described in strong-field approximation, neglecting the Coulomb interaction between the emitted photoelectron (PE) and the residual ion. By solving the time-dependent Schrödinger equation, we identify a temporal shift δτ in streaked PE spectra, which becomes significant at low PE energies. Within an eikonal approximation, we trace this shift to the combined action of Coulomb and laser forces on the released PE, suggesting the experimental and theoretical scrutiny of their coupling in streaked PE spectra. Further, we examined the effect of initial state polarization by the laser pulse on the xuv streaked spectrum.

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Streaked photoemission metrology allows the observation of an apparent relative time delay between the detection of photoelectrons from different initial electronic states. This relative delay is obtained by recording the photoelectron yield as a function of the delay between an ionizing ultrashort extended ultraviolet pulse and a streaking infrared (IR) pulse. Theoretically, photoemission delays can be defined based on (i) the phase shift the photoelectron wave function accumulates during the release and propagation of the photoelectron ("Wigner delay") and, alternatively, (ii) the streaking trace in the calculated photoemission spectrum ("streaking delay"). We investigate the relation between Wigner and streaking delays in the photoemission from atomic and solid-surface targets. For solid targets and assuming a vanishing IR skin depth, both Wigner and streaking delays can be interpreted as an average propagation time needed by photoelectrons to reach the surface, while the two delays differ for nonvanishing skin depths. For atomic targets, the difference between Wigner and streaking delays depends on the range of the ionic potential.

Gemcitabine has limited clinical benefits in pancreatic ductal adenocarcinoma. The solvent-based traditional taxanes docetaxel and paclitaxel have not shown clinical results superior to gemcitabine. Nab-paclitaxel, a water-soluble albumin-bound paclitaxel, may carry superior distribution properties into the tumor microenvironment and has shown efficacy in multiple tumor types. We evaluated nab-paclitaxel effects compared with gemcitabine or docetaxel. For pancreatic ductal adenocarcinoma cells AsPC-1, BxPC-3, MIA PaCa-2 and Panc-1, gemcitabine IC50 ranged from 494nM to 23.9 μM; docetaxel IC50 range was from 5 to 34nM; nab-paclitaxel IC50 range was from 243nM to 4.9 μM. Addition of IC25 dose of docetaxel or nab-paclitaxel decreased gemcitabine IC50. Net tumor growth inhibition after gemcitabine, docetaxel or nab-paclitaxel was 67, 31 and 72%, which corresponded with intratumoral proliferative and apoptotic indices. Tumor stromal density was decreased by nab-paclitaxel and to a lesser extent by docetaxel as measured through reduction in α-smooth muscle actin, S100A4 and collagen 1 expression. Animal survival was prolonged after nab-paclitaxel treatment (41 days, P < 0.002) compared with gemcitabine (32 days, P = 0.005), docetaxel (32 days, P = 0.005) and controls (20 days). Survival in nab-paclitaxel/gemcitabine and docetaxel/gemcitabine sequential treatment groups was not superior to nab-paclitaxel alone. Low-dose combination of gemcitabine with nab-paclitaxel or docetaxel was more effective compared with controls or gemcitabine alone but not superior to regular dose nab-paclitaxel alone. Combination treatment of gemcitabine+nab-paclitaxel or gemcitabine+docetaxel increased gemcitabine concentration in plasma and tumor. The superior antitumor activity of nab-paclitaxel provides a strong rationale for considering nab-paclitaxel as first-line monotherapy in pancreatic ductal adenocarcinoma.