Intrinsic chirp of attosecond pulses: Single-atom model versus experiment

We demonstrate and evaluate the importance of an intrinsic chirp inherent to attosecond pulse creation accompanying high-order harmonic generation in recently published experimental data by Dinu [Phys. Rev. Lett. 91, 063901 (2003)]. We present an analytical model, from which the atomic origin of the harmonic chirp is clearly understood. Moreover, the behavior of the chirp as a function of experimental parameters such as laser intensity is inferred. The comparison between our model and the experimental data provides us with useful information about the conditions in which the high-order harmonics is generated.