Cavity-enhanced field-resolved spectroscopy

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Abstract
Femtosecond enhancement cavities1 are key to applications including high-sensitivity linear2–4 and nonlinear5,6 gas spectroscopy, as well as efficient nonlinear optical frequency conversion7–10. Yet, to date, the broadest simultaneously enhanced bandwidths amount to 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 response16. 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.
Funding Information
  • Canada First Research Excellence Fund
  • Max Planck-UBC-UTokyo Center for Quantum Materials
  • Technology Transfer Program of the Max Planck Society Max Planck-UBC-UTokyo Center for Quantum Materials
  • Max-Planck-Gesellschaft
  • IMPRS-APS graduate school Max-Planck School of Photonics German Federal Ministry of Education and Research, Photonics Research Germany, “SARSCoV2Dx”
  • IMPRS-APS graduate school

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