2015: Spatial properties of isolated low-order harmonics generated in intense laser fields�

Physicists from M.V. Lomonosov MSU (Prof. Anatoly Andreev, Assoc. Prof. Sergey Stremoukhov, Chair of General Physics and Wave Processes and Chair of Optics, Spectroscopy, and Physics of Nanosystems) in collaboration with their colleagues from France and Italy studied for the first time the characteristics of the completely isolated low-order harmonics generated in the process of non-linear interaction of the two-colour laser fields with gas media.

The effect of high harmonic generation in gases serves as effective source of soft X-ray femtosecond pulses. The practical applications of this source depend considerably on the perfection of generated beam properties, especially, on their spatial uniformity. In the research performed by collaboration of scientists from Laboratoire d�Optique Appliquée (France), Centro Ricerche Frascati (Italy), and Faculty of Physics of M.V. Lomonosov Moscow State University was for the first time made the detailed experimental study of completely isolated low-order harmonics obtained with interferential filtering from the wide harmonic spectrum. The detailed comparison of intensity spatial profiles for odd and even harmonics has been made. A significant impact of laser beam aberrations on the spatial distribution of the second harmonic (generated in the BBO crystal) was established. Comparisons of the spatial intensity profiles, of the spatial coherence and of the wavefront aberration level of 5ω at 160 nm and 6ω at 135 nm have then been performed. It has been established that the fundamental laser beam aberrations can cause the appearance of a non-homogenous donut-shape in the 6ω spatial intensity distribution. This undesirable effect can be easily controlled. Methods of optimizing the quality of the spatial distribution of the generated emission were proposed.

The results of this work have been published in the paper: G. Lambert, A. Andreev, J. Gautier, L. Giannessi, V. Malka, A. Petralia, S. Sebban, S. Stremoukhov, F. Tissandier, B. Vodungbo, Ph. Zeitoun, �Spatial properties of odd and even low order harmonics generated in gas�, Scientific Reports 5, 7786 (2015).