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Photon-level broadband spectroscopy and interferometry with two frequency combs

2020; National Academy of Sciences; Volume: 117; Issue: 43 Linguagem: Inglês

10.1073/pnas.2010878117

1091-6490

N. Picqué, Theodor W. Hänsch,

Spectroscopy and Laser Applications

We demonstrate single-photon time-domain interference in a new realm. We observe interferences in the photon counting statistics with two separate mode-locked femtosecond lasers of slightly different repetition frequencies, each emitting a comb of evenly spaced spectral lines over a wide spectral span. We exploit the interference pattern for spectroscopic diagnostics over a broad spectral range. An experimental proof-of-concept shows that the emerging technique of high-resolution dual-comb Fourier transform spectroscopy can be performed at light powers that are a billion-fold weaker than those commonly employed. Our experiments challenge the intuitive concept that a photon exists before detection and they open the prospect of precise spectroscopy over broad spectral bandwidth in light-starved conditions.