Extreme-ultraviolet high-order harmonic generation from few-cycle annular beams

An annular infrared (IR) laser beam has been used for high-order harmonic generation reaching a cut-off energy of 90 eV for extreme-ultraviolet-infrared (XUV-IR) pump-probe experiments in an intrinsically stable attosecond beamline. The generation of harmonics along the laser axis in the missing portion of the laser beam decreases the IR power load on thin metallic foils that are used for removing the residual IR and shaping the XUV pulses from high-harmonic generation. This finds applications in high-average-power few-cycle laser systems, where high-average IR power destroys the foils. The spatial separation of IR and XUV will, moreover, simplify the realization of attosecond time-resolved measurements.