Proof-of-Concept Experiment on Quasi-Phase-Matching of High-Order Harmonic Generation Using a Transverse Disruptive Pulse and Selected-Zoning Method

Quasi-phase-matching of high-order harmonic generation (QPM-HHG) based on the transverse selective-zoning method [1] is demonstrated experimentally. The experimental setup is shown in Fig. 1(a). A driving pulse (810 nm, 42 fs, 1.05 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> W/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, S-polarized) is focused onto the Ar gas jet for HHG and a 2-D EUV flat-field spectrometer measures the 31st HHG. The focal spot size is 87 μm (FWHM), corresponding to a Rayleigh range of 39 mm which is much larger than the outlet diameter of the pulsed valve (1.6 mm). The transverse disruptive pulse polarized in the same direction passes through a delay line and then overlaps transversely with the driving pulse on the Ar gas jet. Its pulse duration is stretched to 3.3 ps (2.44 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> W/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>), ensuring complete spatial-temporal overlap with the driving pulse from the entrance to the end of the Ar gas jet. Two knife edges installed on the moving stages are put in the beamline to control the transverse pulse beam profile, and a lens is inserted to image the beam profile after the knife edges onto the gas jet for interaction length control in tomography or QPM.