Cavity-enhanced field-resolved spectroscopy

• Published in: Nature photonics Vol. 16; no. 10; pp. 692 - 697
• Main Authors: Sulzer, Philipp, Högner, Maximilian, Raab, Ann-Kathrin, Fürst, Lukas, Fill, Ernst, Gerz, Daniel, Hofer, Christina, Voronina, Liudmila, Pupeza, Ioachim
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.10.2022; Nature Publishing Group
• Subjects: 140/125; 639/624/1107/527/2257; 639/624/1111/1112; 639/766/400/385; Applied and Technical Physics; Atom and Molecular Physics and Optics; Atom- och molekylfysik och optik; Couplers; Coupling (molecular); Diamonds; Electric fields; Excitation spectra; Fysik; Gas mixtures; Gold; Gold coatings; Letter; Natural Sciences; Naturvetenskap; Nonlinear optics; Optical frequency; Physical Sciences; Physics; Physics and Astronomy; Quantum Physics; Spectroscopy; Spectrum analysis; Time domain analysis; Vibrations; Waveforms
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/s41566-022-01057-0

Femtosecond enhancement cavities 1 are key to applications including high-sensitivity linear 2 – 4 and nonlinear 5 , 6 gas spectroscopy, as well as efficient nonlinear optical frequency conversion 7 – 10 . Yet, to date, the broadest simultaneously enhanced bandwidths amount to <20% of the central optical frequency 8 , 9 , 11 – 15 . Here, we present an ultrabroadband femtosecond enhancement cavity comprising gold-coated mirrors and a wedged-diamond-plate input coupler, with an average finesse of 55 for optical frequencies below 40 THz and exceeding 40 in the 120–300 THz range. Resonant enhancement of a 50-MHz-repetition-rate offset-free frequency comb spanning 22–40 THz results in a waveform-stable ultrashort circulating pulse with a spectrum supporting a Fourier limit of 1.6 cycles, enabling time-domain electric-field-resolved spectroscopy of molecular samples with temporally separated excitation and molecular response 16 . The contrast between the two is improved by taking advantage of destructive interference at the input coupler. At an effective interaction length with a gas of up to 81 m, this concept promises parts-per-trillion-level ultrabroadband electric-field-resolved linear and nonlinear spectroscopy of impulsively excited molecular vibrations. An ultrabroadband femtosecond enhancement cavity is developed, using gold-coated mirrors and a wedged-diamond-plate input coupler. Simultaneous enhancement of a 22–40 THz offset-free frequency comb allows cavity-enhanced time-domain spectroscopy of gas mixtures based on electro-optic sampling in the mid-infrared range.