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Item A method to generate a single sub-50-as pulse by employing a 5-fs laser pulse with intensity above the saturation intensity, was proposed. The neon target medium of 0.5 mm length and 5 Torr pressure, was placed 10 mm beyond the laser focus. Harmonic radiation from neon atoms, was obtained by solving the time-dependent Schrödinger equation coupled with Maxwell equations. The results show that the positive chirp contained in the broad continuum radiation can be compensated by an x-ray filter with a negative group delay dispersion in the spectral region of interest.(American Physical Society, Single sub-50-attosecond pulse generation from chirp-compensated harmonic radiation using material dispersion) Kim, K.T.; Kim, C.M.; Baik, M.G.; Umesh, G.; Nam, C.H.2004Item Ultrafast dynamics of autoionizing states in O2 probed by laser-field-assisted XUV photoionization(2013) Zhu, C.; Ko, D.H.; Kang, K.S.; Lee, J.; Lee, J.-H.; Umesh, G.; Krishnakumar, E.; Nam, C.H.Dynamics of the autoionizing states in O2 was investigated using the method of laser-field-assisted extreme-ultraviolet photoionization. Harmonics, ranging from 9th to 21st orders generated in Kr with 25 fs laser pulses at 820 nm, were employed to carry out photoionization of O2. Distinct autoionization features in the photoelectron spectrum, stemming from the resonant excitation of superexcited states of O2 by the 11th harmonic, were observed. The superexcited states, referred to as autoionizing states, were identified to be the ?? = 0, n = 5 Rydberg states converging to the b 4?g- state of O 2+. Infrared laser pulses were utilized as the probe to monitor time-varying characteristics of photoionization and autoionization of O2. A decay time of 21 fs was obtained for the autoionizing states of O2 by deconvoluting the pump-probe results in O2 and Ar. © 2013 American Physical Society.