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).

Article 
ADS 

Google Scholar
 

Beck, B. R. et al. Energy splitting of the ground-state doublet in the nucleus 229Th. Phys. Rev. Lett. 98, 142501 (2007).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Seiferle, B. et al. Energy of the 229Th nuclear clock transition. Nature 573, 243–246 (2019).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Masuda, T. et al. X-ray pumping of the 229Th nuclear clock isomer. Nature 573, 238–242 (2019).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Sikorsky, T. et al. Measurement of the 229Th isomer energy with a magnetic microcalorimeter. Phys. Rev. Lett. 125, 142503 (2020).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Kraemer, S. et al. Observation of the radiative decay of the 229Th nuclear clock isomer. Nature 617, 706–710 (2023).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Peik, E. & Tamm, C. Nuclear laser spectroscopy of the 3.5 eV transition in Th-229. Europhys. Lett. 61, 181 (2003).

Article 
ADS 
CAS 

Google Scholar
 

Campbell, C. J. et al. Single-ion nuclear clock for metrology at the 19th decimal place. Phys. Rev. Lett. 108, 120802 (2012).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

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).

Article 
ADS 
PubMed 

Google Scholar
 

Kazakov, G. A. et al. Performance of a 229Thorium solid-state nuclear clock. New J. Phys. 14, 083019 (2012).

Article 
ADS 

Google Scholar
 

Beeks, K. et al. Growth and characterization of thorium-doped calcium fluoride single crystals. Sci. Rep. 13, 3897 (2023).

Article 
ADS 
CAS 
PubMed 
PubMed Central 

Google Scholar
 

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).

Article 
ADS 
CAS 

Google Scholar
 

Zhang, C. et al. Tunable VUV frequency comb for 229mTh nuclear spectroscopy. Opt. Lett. 47, 5591–5594 (2022).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Tiedau, J. et al. Laser excitation of the Th-229 nucleus. Phys. Rev. Lett. 132, 182501 (2024).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Elwell, R. et al. Laser excitation of the 229Th nuclear isomeric transition in a solid-state host. Phys. Rev. Lett. 133, 013201 (2024).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Zhang, C. et al. Frequency ratio of the 229mTh nuclear isomeric transition and the 87Sr atomic clock. Nature 633, 63–70 (2024).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Beeks, K. et al. The thorium-229 low-energy isomer and the nuclear clock. Nat. Rev. Phys. 3, 238–248 (2021).

Article 
CAS 

Google Scholar
 

Hodgson, R. T., Sorokin, P. P. & Wynne, J. J. Tunable coherent vacuum-ultraviolet generation in atomic vapors. Phys. Rev. Lett. 32, 343–346 (1974).

Article 
ADS 
CAS 

Google Scholar
 

Scholz, M. et al. 1.3-mW tunable and narrow-band continuous-wave light source at 191 nm. Opt. Express 20, 18659–18664 (2012).

Article 
ADS 
PubMed 

Google Scholar
 

Schmidt, P. O. et al. Spectroscopy using quantum logic. Science 309, 749–752 (2005).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Marshall, M. C. et al. High-stability single-ion clock with 5.5 × 10−19 systematic uncertainty. Phys. Rev. Lett. 135, 033201 (2025).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Schmidt-Kaler, F. et al. Rydberg excitation of trapped cold ions: a detailed case study. New J. Phys. 13, 075014 (2011).

Article 
ADS 

Google Scholar
 

Zhang, C. et al. Submicrosecond entangling gate between trapped ions via Rydberg interaction. Nature 580, 345–349 (2020).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

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).

Article 
ADS 
MathSciNet 
PubMed 

Google Scholar
 

Kostko, O., Bandyopadhyay, B. & Ahmed, M. Vacuum ultraviolet photoionization of complex chemical systems. Annu. Rev. Phys. Chem. 67, 19–40 (2016).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

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).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Fuchs, E. et al. Searching for dark matter with the 229Th nuclear lineshape from laser spectroscopy. Phys. Rev. X 15, 021055 (2025).

CAS 

Google Scholar
 

Zhang, C. et al. 229ThF4 thin films for solid-state nuclear clocks. Nature 636, 603–608 (2024).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Higgins, J. S. et al. Temperature sensitivity of a thorium-229 solid-state nuclear clock. Phys. Rev. Lett. 134, 113801 (2025).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Terhune, J. E. S. et al. Photo-induced quenching of the 229Th isomer in a solid-state host. Phys. Rev. Res. 7, L022062 (2025).

Article 
CAS 

Google Scholar
 

Schaden, F. et al. Laser-induced quenching of the Th-229 nuclear clock isomer in calcium fluoride. Phys. Rev. Res. 7, L022036 (2025).

Article 
CAS 

Google Scholar
 

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).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Thielking, J. et al. Laser spectroscopic characterization of the nuclear-clock isomer 229mTh. Nature 556, 321–325 (2018).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Scharl, K. et al. Setup for the ionic lifetime measurement of the 229mTh3+ nuclear clock isomer. Atoms 11, 108 (2023).

Article 
ADS 
CAS 

Google Scholar
 

Zitzer, G. et al. Sympathetic cooling of trapped Th3+ alpha-recoil ions for laser spectroscopy. Phys. Rev. A 109, 033116 (2024).

Article 
ADS 
CAS 

Google Scholar
 

Yamaguchi, A. et al. Laser spectroscopy of triply charged 229Th isomer for a nuclear clock. Nature 629, 62–66 (2024).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Leibfried, D., Blatt, R., Monroe, C. & Wineland, D. Quantum dynamics of single trapped ions. Rev. Mod. Phys. 75, 281 (2003).

Article 
ADS 
CAS 

Google Scholar
 

Thirolf, P. Shedding light on the thorium-229 nuclear clock isomer. Physics 17, 71 (2024).

Article 

Google Scholar
 

Mutailipu, M. & Pan, S. Emergent deep-ultraviolet nonlinear optical candidates. Angew. Chem. Int. Ed. 59, 20302–20317 (2020).

Article 
CAS 

Google Scholar
 

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).

Article 
ADS 
PubMed 

Google Scholar
 

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).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Eikema, K. S. E., Walz, J. & Hänsch, T. W. Continuous wave coherent Lyman-α radiation. Phys. Rev. Lett. 83, 3828 (1999).

Article 
ADS 
CAS 

Google Scholar
 

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).

Article 
ADS 
PubMed 

Google Scholar
 

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).

CAS 

Google Scholar
 

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).

Article 
ADS 
CAS 

Google Scholar
 

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).

Article 
ADS 
CAS 

Google Scholar
 

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).

Article 
ADS 
CAS 

Google Scholar
 

Bodine, M. I. et al. Optical atomic clock comparison through turbulent air. Phys. Rev. Res. 2, 033395 (2020).

Article 
CAS 

Google Scholar
 

von der Wense, L. et al. The theory of direct laser excitation of nuclear transitions. Eur. Phys. J. A 56, 176 (2020).

Article 
ADS 

Google Scholar
 

Hiraki, T. et al. Controlling 229Th isomeric state population in a VUV transparent crystal. Nat. Commun. 15, 5536 (2024).

Article 
ADS 
CAS 
PubMed 
PubMed Central 

Google Scholar
 

Matei, D. G. et al. 1.5 μm lasers with sub-10 mHz linewidth. Phys. Rev. Lett. 118, 263202 (2017).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Lal, V. et al. Continuous-wave laser source at the 148 nm nuclear transition of Th-229. Optica 12, 1971–1974 (2025).

Article 
ADS 

Google Scholar
 

Wu, L. et al. 0.26-Hz-linewidth ultrastable lasers at 1557 nm. Sci. Rep. 6, 24969 (2016).

Article 
ADS 
CAS 
PubMed 
PubMed Central 

Google Scholar
 

Fienup, J. R. Phase retrieval algorithms: a comparison. Appl. Opt. 21, 2758–2769 (1982).

Article 
ADS 
CAS 
PubMed 

Google Scholar
 

Riley, D. S. & Karam, S. L. The Allan variance and its applications to frequency stability measurements. Proc. IEEE 82, 1250–1259 (1994).


Google Scholar
 

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).

Article 
ADS 
PubMed 

Google Scholar
 

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).

Article 
ADS 
CAS 

Google Scholar
 

Larkin, K. G. Efficient nonlinear algorithm for envelope detection in white-light interferograms. J. Opt. Soc. Am. A 13, 832–843 (1996).

Article 
ADS 

Google Scholar
 

Rutman, J. Characterization of phase and frequency instabilities in precision frequency sources: fifteen years of progress. Proc. IEEE 66, 1048–1075 (1978).

Article 
ADS 

Google Scholar
 

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).

Article 
ADS 
PubMed 

Google Scholar
 

Fortier, T. & Baumann, E. 20 years of developments in optical frequency comb technology and applications. Commun. Phys. 2, 153 (2019).

Article 

Google Scholar
 

Photomultiplier Tubes: Basics and Applications 4th edn (Hamamatsu Photonics K. K., 2017).