Observation and origin of multi-THz quantum beats in superfluorescent emission from argon

Journal Article · 26 January 2025 · Physical Review A

DOI: https://doi.org/10.1103/physreva.111.013116 · OSTI ID:2506759

Nambu, Noa  ^[1]; Nie, Zan  ^[2]; Marsh, Ken  ^[1]; Patel, C. Kumar N.  ^[3]; Smirnova, Olga  ^[4]; Ivanov, Misha  ^[4]; Joshi, Chan  ^[1]

---

1. University of California, Los Angeles, CA (United States)
2. University of California, Los Angeles, CA (United States); Huazhong University of Science and Technology, Wuhan (China)
3. University of California, Los Angeles, CA (United States); QCL Systems, Los Angeles, CA (United States)
4. Max Born Institute, Berlin (Germany)

We report observation of multi-THz quantum beats in the amplitude of superfluorescence in pure argon gas, using a time delayed 780-nm probe beam that interrogates the relevant population densities. The superfluorescence is induced by three-photon absorption of an ultrashort 260.5-nm laser pulse that creates coherent and coupled populations in multiple closely spaced 3⁢d and 5⁢s Ar levels. Argon pressure and pump laser focusing parameters are seen to modify the frequency of the quantum beats, which is attributed to the absorption of the self-generated, nonresonant third harmonic of the pump from Ar near the zero of the real part of the overlapping linear susceptibilities of the closely spaced 3⁢d and 5⁢s excited states. The self-absorption of the phase-matched THG photons creates a coherent population of atoms which acts like an atomic excited state (3⁢ω-induced state). Furthermore, we have also observed a new two-step superfluorescent cascade that results from the population redistribution enabled by the 780-nm probe pulse between the 3⁢d'[5/2]₃ and the 3⁢ω-induced state and gives rise to a previously unknown transition that emits on 1587 nm.

• Research Organization: Univ. of California, Los Angeles, CA (United States); University of California, Los Angeles, CA (United States)
• Sponsoring Organization: National Natural Science Foundation of China; National Science Foundation (NSF); Office of Naval Research (ONR); USDOE; USDOE Office of Science (SC), High Energy Physics (HEP)
• Grant/Contract Number: SC0010064
• OSTI ID: 2506759
• Journal Information: Physical Review A, Journal Name: Physical Review A Journal Issue: 1 Vol. 111; ISSN 2469-9926
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English