Transient absorption of attosecond pulse trains by laser-dressed helium

Shaohao Chen, Louisiana State University
Kenneth J. Schafer, Louisiana State University
Mette B. Gaarde, Louisiana State University


We investigate transient absorption of high harmonics in an attosecond pulse train by laser-dressed He atoms using both single-atom and macroscopic methods. Calculations of the absorption as a function of laser wavelength and intensity reveal that the absorption probability is tied to resonant laser-dressed atomic states. We report for the first time to our knowledge a quarter-laser-cycle modulation in the absorption (mixed with the well-known half-cycle modulation). We discuss the conditions for which this high-order coupling could be observed and the role that the reshaping of the attosecond pulses in the medium plays in the timing of absorption. © 2012 Optical Society of America.