Spatial profiles of high-order harmonics generated by a femtosecond cr:Lisaf laser

Summary, in English

We report the angular distributions of high-order harmonic radiation generated in neon and in argon using a 140 fs Cr:LisAF laser system. The profiles show an evolution from Gaussian to near flat-top. No substructure is observed except at the highest intensity in a completely ionized gas. The divergence of the harmonics is found to depend essentially on whether they belong to the plateau or to the cutoff. It is approximately constant in the plateau, of the order of 15 mrad and decreases from 15 mrad to 6 mrad in the cutoff region.