Frequency chirp of harmonic and attosecond pulses

K. Varjú, Lunds Tekniska Högskola
Y. Mairesse, Service des Photons Atomes et Molécules
B. Carré, Service des Photons Atomes et Molécules
M. B. Gaarde, Louisiana State University
P. Johnsson, Lunds Tekniska Högskola
S. Kazamias, Laboratoire d'Optique Appliquée
R. López-Martens, Laboratoire d'Optique Appliquée
J. Mauritsson, Louisiana State University
K. J. Schafer, Louisiana State University
Ph Balcou, Laboratoire d'Optique Appliquée
A. L'Huillier, Lunds Tekniska Högskola
P. Salières, Service des Photons Atomes et Molécules


We study the phase of the atomic polarization in the process of high-order harmonic generation. Its dependence on the laser intensity and the harmonic order induce a frequency variation in time (chirp) respectively of the harmonic pulses and attosecond pulses. We review the recent experimental results on the temporal characterization of the harmonic emission and show that measurements performed using very different techniques (like XFROG and RABITT), probing the phase in different parameter spaces, can be connected through the mixed phase derivatives, demonstrating the common underlying physics.