1.Department of Physics and Astronomy & Institute of Applied Physics, Seoul National University, Seoul, Korea
2.Korea Research Institute of Standards and Science, Daejeon, Korea
Kyungwon An (kwan@phya.snu.ac.kr)
Published:30 November 2024,
Published Online:05 September 2024,
Received:18 March 2024,
Revised:14 August 2024,
Accepted:19 August 2024
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Oh, S. H. et al. Thresholdless coherence in a superradiant laser. Light: Science & Applications, 13, 2549-2555 (2024).
Oh, S. H. et al. Thresholdless coherence in a superradiant laser. Light: Science & Applications, 13, 2549-2555 (2024). DOI: 10.1038/s41377-024-01591-2.
Lasing threshold in the conventional lasers is the minimum input power required to initiate laser oscillation. It has been widely accepted that the conventional laser threshold occurring around a unity intracavity photon number can be eliminated in the input-output curve by making the so-called
β
parameter approach unity. The recent experiments
however
have revealed that even in this case the photon statistics still undergo a transition from coherent to thermal statistics when the intracavity mean photon number is decreased below unity. Since the coherent output is only available above the diminished threshold
the long-sought promise of thresholdless lasers to produce always coherent light has become questionable. Here
we present an always-coherent thresholdless laser based on superradiance by two-level atoms in a quantum superposition state with the same phase traversing a high-Q cavity. Superradiant lasing was observed without the conventional lasing threshold around the unity photon number and the photon statistics remained near coherent even below it. The coherence was improved by reducing the coupling constant as well as the excited-state amplitude in the superposition state. Our results pave a way toward always-coherent thresholdless lasers with more practical media such as quantum dots
nitrogen-vacancy centers and doped ions in crystals.
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