Surface harmonics generation with a 100 TW table-top laser system

The interaction of an extremely intense laser beam with the dense plasma generated on a solid target can lead to coherent electron dynamics at the vacuum plasma interface which causes the emission of ultra short light bursts within each optical cycle of the driving laser pulse. Therefore, the resulting pulse train consists of high harmonics of the laser fundamental frequency. We report on the, to our knowledge, first observation of surface-harmonics up to the 42nd order without any contrast improvement by a plasma mirror. In the spectral region from the 25th to the 40th order approximately 10 7 photons were detected in a solid angle of 4 • 10 -4 sr.