[1] Pupeza I, Zhang C K, Högner M et al. Extreme-ultraviolet frequency combs for precision metrology and attosecond science[J]. Nature Photonics, 15, 175-186(2021).

[2] Eyler E E, Chieda D E, Stowe M C et al. Prospects for precision measurements of atomic helium using direct frequency comb spectroscopy[J]. The European Physical Journal D, 48, 43-55(2008).

[3] Nauta J, Borodin A, Ledwa H B et al. Towards precision measurements on highly charged ions using a high harmonic generation frequency comb[J]. Nuclear Instruments and Methods in Physics Research Section B, 408, 285-288(2017).

[4] von der Wense L, Zhang C K. Concepts for direct frequency-comb spectroscopy of 229mTh and an internal-conversion-based solid-state nuclear clock[J]. The European Physical Journal D, 74, 146(2020).

[5] Tiedau J, Okhapkin M V, Zhang K et al. Laser excitation of the Th-229 nucleus[J]. Physical Review Letters, 132, 182501(2024).

[6] Elwell R, Schneider C, Jeet J et al. Laser excitation of the 229Th nuclear isomeric transition in a solid-state host[J]. Physical Review Letters, 133, 013201(2024).

[7] Allison T, Cingoz A, Yost D et al. Extreme nonlinear optics in a femtosecond enhancement cavity[J]. Physical Review Letters, 107, 183903(2011).

[8] Benko C, Hua L Q, Allison T K et al. Cavity-enhanced field-free molecular alignment at a high repetition rate[J]. Physical Review Letters, 114, 153001(2015).

[9] Yost D C, Schibli T R, Ye J et al. Vacuum-ultraviolet frequency combs from below-threshold harmonics[J]. Nature Physics, 5, 815-820(2009).

[10] Hostetter J A, Tate J L, Schafer K J et al. Semiclassical approaches to below-threshold harmonics[J]. Physical Review A, 82, 023401(2010).

[11] Na M X, Mills A K, Boschini F et al. Direct determination of mode-projected electron-phonon coupling in the time domain[J]. Science, 366, 1231-1236(2019).

[12] Mills A K, Zhdanovich S, Na M X et al. Cavity-enhanced high harmonic generation for extreme ultraviolet time- and angle-resolved photoemission spectroscopy[J]. The Review of Scientific Instruments, 90, 083001(2019).

[13] Corder C, Zhao P, Bakalis J et al. Ultrafast extreme ultraviolet photoemission without space charge[J]. Structural Dynamics, 5, 054301(2018).

[14] Lee J, Carlson D R, Jones R J. Optimizing intracavity high harmonic generation for XUV fs frequency combs[J]. Optics Express, 19, 23315-23326(2011).

[15] Porat G, Heyl C M, Schoun S B et al. Phase-matched extreme-ultraviolet frequency-comb generation[J]. Nature Photonics, 12, 387-391(2018).

[16] Yost D C, Schibli T R, Ye J. Efficient output coupling of intracavity high-harmonic generation[J]. Optics Letters, 33, 1099-1101(2008).

[17] Pupeza I, Holzberger S, Eidam T et al. Compact high-repetition-rate source of coherent 100 eV radiation[J]. Nature Photonics, 7, 608-612(2013).

[18] Zhang C K, Schoun S B, Heyl C M et al. Noncollinear enhancement cavity for record-high out-coupling efficiency of an extreme-UV frequency comb[J]. Physical Review Letters, 125, 093902(2020).

[19] Zhang J, Hua L Q, Chen Z et al. Extreme ultraviolet frequency comb with more than 100 μW average power below 100 nm[J]. Chinese Physics Letters, 37, 124203(2020).

[20] Zhang J, Hua L Q, Yu S G et al. Laser-driven fluorescence emission in a nitrogen gas jet at 100 MHz repetition rate[J]. Physical Review A, 103, 032822(2021).

[21] Zhu M F, Zhang J, Hua L Q et al. Molecular structural effects in below- and near-threshold harmonics in XUV-comb generation[J]. Physical Review A, 104, 043111(2021).

[22] Hädrich S, Krebs M, Hoffmann A et al. Exploring new avenues in high repetition rate table-top coherent extreme ultraviolet sources[J]. Light: Science & Applications, 4, e320(2015).

[23] Zhao Z G, Ozawa A, Kuwata-Gonokami M et al. Efficient high harmonics generation by enhancement cavity driven with a post-compressed FCPA laser at 10 MHz[J]. High Power Laser Science and Engineering, 6, e19(2018).

[24] Südmeyer T, Brunner F, Innerhofer E et al. Nonlinear femtosecond pulse compression at high average power levels by use of a large-mode-area holey fiber[J]. Optics Letters, 28, 1951-1953(2003).

[25] Fritsch K, Poetzlberger M, Pervak V et al. All-solid-state multipass spectral broadening to sub-20 fs[J]. Optics Letters, 43, 4643-4646(2018).

[26] Köttig F, Schade D, Koehler J R et al. Efficient single-cycle pulse compression of an ytterbium fiber laser at 10 MHz repetition rate[J]. Optics Express, 28, 9099-9110(2020).

[27] Gohle C, Udem T, Herrmann M et al. A frequency comb in the extreme ultraviolet[J]. Nature, 436, 234-237(2005).

[28] Jones R J, Moll K D, Thorpe M J et al. Phase-coherent frequency combs in the vacuum ultraviolet via high-harmonic generation inside a femtosecond enhancement cavity[J]. Physical Review Letters, 94, 193201(2005).

[29] Black E D. An introduction to Pound-Drever-Hall laser frequency stabilization[J]. American Journal of Physics, 69, 79-87(2001).

[30] Ozawa A, Rauschenberger J, Gohle C et al. High harmonic frequency combs for high resolution spectroscopy[J]. Physical Review Letters, 100, 253901(2008).

[31] Pronin O, Pervak V, Fill E et al. Ultrabroadband efficient intracavity XUV output coupler[J]. Optics Express, 19, 10232-10240(2011).

[32] Moll K D, Jones R J, Ye J. Output coupling methods for cavity-based high-harmonic generation[J]. Optics Express, 14, 8189-8197(2006).

[33] Xiao Z R, Zhu M F, Zhang J et al. Comparison of out-coupling methods for extreme ultraviolet comb[J]. Acta Optica Sinica, 42, 1134015(2022).

[34] Qi R Z, Zhang J L, Wu J L et al. Thin film optical elements in extreme ultraviolet and vacuum ultraviolet[J]. Acta Optica Sinica, 42, 1134003(2022).

[35] Zhang J, Hua L Q, Yu S G et al. Femtosecond enhancement cavity with kilowatt average power[J]. Chinese Physics B, 28, 044206(2019).

[36] Moharam M G, Grann E B, Pommet D A et al. Formulation for stable and efficient implementation of the rigorous coupled-wave analysis of binary gratings[J]. Journal of the Optical Society of America A, 12, 1068-1076(1995).