Cavity-enhanced field-resolved spectroscopy

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 <20% of the central optical frequency8,9,11–15. 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.

Planar photonic chips with tailored dispersion relations for high-efficient spectrographic devices

“…Spectral detection, as a rapid and non-contact characterization method, is widely used in biochemical analysis, substance identification, and pharmaceutical, medical research and also industry 1,2,3,4,5,6,7,8,9,10,11 . Commercially spectrometers employed gratings or interferometers, are always bulky and time-consuming.…”

Dual-comb optomechanical spectroscopy

“…Ultrasensitive DCS has been investigated using hollow-core fibers 7 , multi-pass cells 8 , or optical resonance cavities [9][10][11] to enhance absorption and, consequently, sensitivity. Among these demonstrations, cavity-enhanced schemes, with unmatched pathlength enhancement, yield the lowest detection limitspossibly down to the parts-per-trillion (ppt) level.…”

“…The resonance cavities, however, essentially restrict the wavelength range of operation and lead to difficulties, respecting mirror coating, comb-cavity coupling, dispersion, etc., for broadband measurements. Meticulous electronic controls and cavity designs 10,11 may alleviate these difficulties at the cost of increased system complexity and limited applicability. More generally, the above systems with long light-molecule-interaction lengths are bulky and may suffer from large sample volumes and low gas exchange rates, preventing their applications for real-time, in-situ gas monitoring.…”