Generation of 10 μW relativistic surface high-harmonic radiation at a repetition rate of 10 Hz

Experimental results on relativistic surface HHG at a repetition rate of 10 Hz are presented. Average powers in the 10  μ W range are generated in the spectral range of 51 to 26 nm (24–48 eV). The surface harmonic radiation is produced by focusing the second-harmonic of a high-power laser onto a rotating glass surface to moderately relativistic intensities of 3  ×  10 19  W cm −2 . The harmonic emission exhibits a divergence of 26 mrad. Together with absolute photon numbers recorded by a calibrated spectrometer, this allows for the determination of the extreme ultraviolet (XUV) yield. The pulse energies of individual harmonics are reaching up to the μ J level, equivalent to an efficiency of 10 −5 . The capability of producing stable and intense high-harmonic radiation from relativistic surface plasmas may facilitate experiments on nonlinear ionization or the seeding of free-electron lasers.