Abstract

Important processes initiated by light absorption in matter are known to evolve on an ultrafast time-scale [1]. Nowadays, the availability of sources of attosecond pulses allows investigating such mechanisms with the required temporal resolution. Recently, P. Johnsson and co-workers, applied a train of attosecond pulses (APT) in combination with a synchronized few-cycle infrared (IR) field in a pump-probe scheme, to study the photoionization of helium (He) around the first ionization threshold [2]. We study the optical response in the same physical system with transient absorption using APTs in combination with elliptically polarized IR pulses or single attosecond pulses (SAPs). Our new results indicate that the wavepacket picture given in Ref. [2] is insufficient to explain the optical response of the system.

© 2013 IEEE