Kroger, L. A. & Reich, C. W. Features of the low-energy level scheme of 229Th as observed in the α-decay of 233U. Nucl. Phys. A 259, 29–60 (1976).
Beck, B. R. et al. Energy splitting of the ground-state doublet in the nucleus 229Th. Phys. Rev. Lett. 98, 142501 (2007).
Seiferle, B. et al. Energy of the 229Th nuclear clock transition. Nature 573, 243–246 (2019).
Masuda, T. et al. X-ray pumping of the 229Th nuclear clock isomer. Nature 573, 238–242 (2019).
Sikorsky, T. et al. Measurement of the 229Th isomer energy with a magnetic microcalorimeter. Phys. Rev. Lett. 125, 142503 (2020).
Kraemer, S. et al. Observation of the radiative decay of the 229Th nuclear clock isomer. Nature 617, 706–710 (2023).
Peik, E. & Tamm, C. Nuclear laser spectroscopy of the 3.5 eV transition in Th-229. Europhys. Lett. 61, 181 (2003).
Campbell, C. J. et al. Single-ion nuclear clock for metrology at the 19th decimal place. Phys. Rev. Lett. 108, 120802 (2012).
Rellergert, W. G. et al. Constraining the evolution of the fundamental constants with a solid-state optical frequency reference based on the 229Th nucleus. Phys. Rev. Lett. 104, 200802 (2010).
Kazakov, G. A. et al. Performance of a 229Thorium solid-state nuclear clock. New J. Phys. 14, 083019 (2012).
Beeks, K. et al. Growth and characterization of thorium-doped calcium fluoride single crystals. Sci. Rep. 13, 3897 (2023).
Jeet, J. Search for the Low Lying Transition in the 229Th Nucleus. Dissertation, Univ. California, Los Angeles (2018).
Thielking, J. et al. Vacuum-ultraviolet laser source for spectroscopy of trapped thorium ions. New J. Phys. 25, 083026 (2023).
Zhang, C. et al. Tunable VUV frequency comb for 229mTh nuclear spectroscopy. Opt. Lett. 47, 5591–5594 (2022).
Tiedau, J. et al. Laser excitation of the Th-229 nucleus. Phys. Rev. Lett. 132, 182501 (2024).
Elwell, R. et al. Laser excitation of the 229Th nuclear isomeric transition in a solid-state host. Phys. Rev. Lett. 133, 013201 (2024).
Zhang, C. et al. Frequency ratio of the 229mTh nuclear isomeric transition and the 87Sr atomic clock. Nature 633, 63–70 (2024).
Beeks, K. et al. The thorium-229 low-energy isomer and the nuclear clock. Nat. Rev. Phys. 3, 238–248 (2021).
Hodgson, R. T., Sorokin, P. P. & Wynne, J. J. Tunable coherent vacuum-ultraviolet generation in atomic vapors. Phys. Rev. Lett. 32, 343–346 (1974).
Scholz, M. et al. 1.3-mW tunable and narrow-band continuous-wave light source at 191 nm. Opt. Express 20, 18659–18664 (2012).
Schmidt, P. O. et al. Spectroscopy using quantum logic. Science 309, 749–752 (2005).
Marshall, M. C. et al. High-stability single-ion clock with 5.5 × 10−19 systematic uncertainty. Phys. Rev. Lett. 135, 033201 (2025).
Schmidt-Kaler, F. et al. Rydberg excitation of trapped cold ions: a detailed case study. New J. Phys. 13, 075014 (2011).
Zhang, C. et al. Submicrosecond entangling gate between trapped ions via Rydberg interaction. Nature 580, 345–349 (2020).
Zhou, X. et al. New developments in laser-based photoemission spectroscopy and its scientific applications: a key issues review. Rep. Prog. Phys. 81, 062101 (2018).
Kostko, O., Bandyopadhyay, B. & Ahmed, M. Vacuum ultraviolet photoionization of complex chemical systems. Annu. Rev. Phys. Chem. 67, 19–40 (2016).
Flambaum, V. V. Enhanced effect of temporal variation of the fine structure constant and the strong interaction in 229Th. Phys. Rev. Lett. 97, 092502 (2006).
Fuchs, E. et al. Searching for dark matter with the 229Th nuclear lineshape from laser spectroscopy. Phys. Rev. X 15, 021055 (2025).
Zhang, C. et al. 229ThF4 thin films for solid-state nuclear clocks. Nature 636, 603–608 (2024).
Higgins, J. S. et al. Temperature sensitivity of a thorium-229 solid-state nuclear clock. Phys. Rev. Lett. 134, 113801 (2025).
Terhune, J. E. S. et al. Photo-induced quenching of the 229Th isomer in a solid-state host. Phys. Rev. Res. 7, L022062 (2025).
Schaden, F. et al. Laser-induced quenching of the Th-229 nuclear clock isomer in calcium fluoride. Phys. Rev. Res. 7, L022036 (2025).
Campbell, C. J., Radnaev, A. G. & Kuzmich, A. Wigner crystals of 229Th for optical excitation of the nuclear isomer. Phys. Rev. Lett. 106, 223001 (2011).
Thielking, J. et al. Laser spectroscopic characterization of the nuclear-clock isomer 229mTh. Nature 556, 321–325 (2018).
Scharl, K. et al. Setup for the ionic lifetime measurement of the 229mTh3+ nuclear clock isomer. Atoms 11, 108 (2023).
Zitzer, G. et al. Sympathetic cooling of trapped Th3+ alpha-recoil ions for laser spectroscopy. Phys. Rev. A 109, 033116 (2024).
Yamaguchi, A. et al. Laser spectroscopy of triply charged 229Th isomer for a nuclear clock. Nature 629, 62–66 (2024).
Leibfried, D., Blatt, R., Monroe, C. & Wineland, D. Quantum dynamics of single trapped ions. Rev. Mod. Phys. 75, 281 (2003).
Thirolf, P. Shedding light on the thorium-229 nuclear clock isomer. Physics 17, 71 (2024).
Mutailipu, M. & Pan, S. Emergent deep-ultraviolet nonlinear optical candidates. Angew. Chem. Int. Ed. 59, 20302–20317 (2020).
Víllora, E. G., Shimamura, K., Sumiya, K. & Ishibashi, H. Birefringent- and quasi phase-matching with BaMgF4 for vacuum-UV/UV and mid-IR all solid-state lasers. Opt. Express 17, 12362–12378 (2009).
Yakar, O., Nitiss, E., Hu, J. & Brès, C.-S. Integrated backward second-harmonic generation through optically induced quasi-phase-matching. Phys. Rev. Lett. 131, 143802 (2023).
Eikema, K. S. E., Walz, J. & Hänsch, T. W. Continuous wave coherent Lyman-α radiation. Phys. Rev. Lett. 83, 3828 (1999).
Kolbe, D., Scheid, M. & Walz, J. Triple resonant four-wave mixing boosts the yield of continuous coherent vacuum ultraviolet generation. Phys. Rev. Lett. 109, 063901 (2012).
Pahl, A. et al. Generation of continuous coherent radiation at Lyman-α and 1S-2P spectroscopy of atomic hydrogen. Laser Phys. 15, 46–54 (2005).
Xiao, Q. et al. Proposal for the generation of continuous-wave vacuum ultraviolet laser light for Th-229 isomer precision spectroscopy. Preprint at https://arxiv.org/abs/2406.16841 (2024).
Benko, C. et al. Extreme ultraviolet radiation with coherence time greater than 1 s. Nat. Photon. 8, 530–536 (2014).
Penyazkov, G., Yu, Y., Skripnikov, L. V. & Ding, S. Theoretical study of transition matrix elements in cadmium for vacuum-ultraviolet generation in 229Th nuclear clock applications. Phys. Rev. A 112, 022807 (2025).
Wang, J. et al. A new instrument of VUV laser desorption/ionization mass spectrometry imaging with micrometer spatial resolution and low level of molecular fragmentation. Rev. Sci. Instrum. 88, 114102 (2017).
Vidal, C. R. in Tunable Lasers (eds Mollenauer, L. F., White, J. C. & Pollock, C. R.) Ch. 3 (Springer, 2005).
Tian, H. et al. Frequency-shifted f-2f interferometer for unveiling the noise performance of carrier-envelope offset in passively stabilized frequency combs. Appl. Phys. Lett. 125, 241107 (2024).
Bodine, M. I. et al. Optical atomic clock comparison through turbulent air. Phys. Rev. Res. 2, 033395 (2020).
von der Wense, L. et al. The theory of direct laser excitation of nuclear transitions. Eur. Phys. J. A 56, 176 (2020).
Hiraki, T. et al. Controlling 229Th isomeric state population in a VUV transparent crystal. Nat. Commun. 15, 5536 (2024).
Matei, D. G. et al. 1.5 μm lasers with sub-10 mHz linewidth. Phys. Rev. Lett. 118, 263202 (2017).
Lal, V. et al. Continuous-wave laser source at the 148 nm nuclear transition of Th-229. Optica 12, 1971–1974 (2025).
Wu, L. et al. 0.26-Hz-linewidth ultrastable lasers at 1557 nm. Sci. Rep. 6, 24969 (2016).
Fienup, J. R. Phase retrieval algorithms: a comparison. Appl. Opt. 21, 2758–2769 (1982).
Riley, D. S. & Karam, S. L. The Allan variance and its applications to frequency stability measurements. Proc. IEEE 82, 1250–1259 (1994).
Riley, W. J. Handbook of frequency stability analysis. National Institute of Standards and Technology https://www.nist.gov/publications/handbook-frequency-stability-analysis (2008).
Makdissi, A., Vernotte, F. & De Clercq, E. Stability variances: a filter approach. IEEE Trans. Ultrason. Ferroelectr. Freq. Control 57, 1011–1028 (2010).
Mandel, L. & Wolf, E. Optical Coherence and Quantum Optics (Cambridge Univ. Press, 1995).
Elliott, D. S., Roy, R. & Smith, S. J. Extracavity laser band-shape and bandwidth modification. Phys. Rev. A 26, 12–18 (1982).
Larkin, K. G. Efficient nonlinear algorithm for envelope detection in white-light interferograms. J. Opt. Soc. Am. A 13, 832–843 (1996).
Rutman, J. Characterization of phase and frequency instabilities in precision frequency sources: fifteen years of progress. Proc. IEEE 66, 1048–1075 (1978).
Domenico, G. D., Schilt, S. & Thomann, P. Simple approach to the relation between laser frequency noise and laser line shape. Appl. Opt. 49, 4801–4807 (2010).
Fortier, T. & Baumann, E. 20 years of developments in optical frequency comb technology and applications. Commun. Phys. 2, 153 (2019).
Photomultiplier Tubes: Basics and Applications 4th edn (Hamamatsu Photonics K. K., 2017).

