Based on high-order harmonic generation (HHG), coherent light sources spanning from the extreme ultraviolet to X-ray regions can be obtained, which can be applied in research such as time- and angle-resolved photoemission spectroscopy (Tr-ARPES), attosecond transient absorption spectroscopy (ATAS), and coherent diffraction imaging (CDI). As the repetition rate and power of HHG driving lasers continue to increase, effectively separating the generated high-order harmonics from the high-power driving laser has become a critical challenge. Typically, components such as grazing incidence plates (GIP), diffraction gratings, microchannel plates (MCP), and drilled mirrors (DM) are used to attenuate the high-power driving laser. However, some of these components lead to substantial loss of high-order harmonic power, or lack sufficient flexibility in optical path design.
This paper presents a method for efficient generation and separation of high-order harmonics using multiple drilled mirrors. The setup includes four drilled mirrors (DM1–DM4), one focusing mirror, one gas jet, and one metal filter. DM1 splits the incident high-power driving laser; DM2 generates an annular driving laser; and DM3 and DM4 are used to separate the residual driving laser. In addition, DM2 and DM3 are positioned at the object plane and image plane of the focusing mirror, respectively.
To validate the proposed method, we utilized a Yb fiber femtosecond laser (central wavelength: 1030 nm, repetition rate: 500 kHz, average power: 208 W, pulse duration: 170 fs) to drive argon gas, generating high-order harmonics with photon energies spanning 27–47 eV. The experimental results demonstrate that the method achieves an attenuation ratio of the driving laser on the order of 10^-3, while enabling nearly lossless transmission of the high-order harmonics. Furthermore, theoretical simulations of the beam profile evolution and power variation during laser propagation confirm the effectiveness of this approach for high-repetition-rate, high-average-power femtosecond laser-driven HHG and efficient harmonic separation. The method is particularly suitable for time-resolved pump–probe experiments and is expected to play a significant role in the future development of large-scale attosecond laser facilities.