Broadband femtosecond lasers enable efficient two-photon excitation of the ultranarrow linewidth singlet 1s2s state in helium

2025/09/17 by Kumar, Shashank, Piel, Justin D., Greene, Chris H. +1
#Atomic Physics (physics.atom-ph) #FOS: Physical sciences #Optics (physics.optics) #Quantum Physics (quant-ph)

paper · doi:10.48550/arxiv.2509.13619

Abstract

We propose a broadband, femtosecond two-photon excitation scheme for efficient population transfer to the ultra-narrow linewidth 1s2s ¹S₀ metastable state in helium. Using 120 nm vacuum ultraviolet (VUV) femtosecond laser pulses, we theoretically demonstrate that a direct two-photon excitation process can achieve a population transfer efficiency of 25-30%, even when photoionization losses are included. The use of broadband pulses enables multiple excitation pathways to populate the excited state, in addition to compensating for significant AC Stark shifts occurring within the pulse duration. Furthermore, we introduce a two-color two-photon extreme ultraviolet-near infrared (XUV-IR) excitation scheme that will further reduce ionization losses and can achieve significantly higher transfer efficiencies of ∼ 70%. These results demonstrate that high excitation probability of ultra-narrow linewidth (∼ 50 Hz) excited states can be achieved with experimentally accessible femtosecond laser sources with a few THz bandwidth.

Citations

• Long-lived metastable-qubit memory
• Frequency ratio of the 229mTh nuclear isomeric transition and the 87Sr atomic clock
• Efficient (∼10%) Generation of Vacuum Ultraviolet Femtosecond Pulses via Four-Wave Mixing in Hollow-Core Fibers
• Attosecond Entangled Photons from Two-Photon Decay of Metastable Atoms: A Source for Attosecond Experiments and Beyond
• Tunable third harmonic generation in the vacuum ultraviolet region using dielectric nanomembranes
• Coherent population transfer among quantum states of atoms and molecules

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