Cavity buildup dispersion spectroscopy

Cavity-enhanced spectroscopy is used to analyse light-matter interactions in fields such as ultracold chemistry and planetary science but measurement performance can be hampered by nonlinearities and long acquisition times. Here, the authors report a technique called cavity build up dispersion spectroscopy to measure dispersive frequency shifts demonstrating increased acquisition speeds and less susceptibility to detector nonlinearity. Measurements of ultrahigh-fidelity absorption spectra can help validate quantum theory, engineer ultracold chemistry, and remotely sense atmospheres. Recent achievements in cavity-enhanced spectroscopy using either frequency-based dispersion or time-based absorption approaches have set new records for accuracy with uncertainties at the sub-per-mil level. However, laser scanning or susceptibility to nonlinearities limits their ultimate performance. Here we present cavity buildup dispersion spectroscopy (CBDS), probing the CO molecule as an example, in which the dispersive frequency shift of a cavity resonance is encoded in the cavity's transient response to a phase-locked non-resonant laser excitation. Beating between optical frequencies during buildup exactly localizes detuning from mode center, and thus enables single-shot dispersion measurements. CBDS can yield an accuracy limited by the chosen frequency standard and measurement duration and is currently 50 times less susceptible to detection nonlinearity compared to intensity-based methods. Moreover, CBDS is significantly faster than previous frequency-based cavity-enhanced methods. The generality of CBDS shows promise for improving fundamental research into a variety of light-matter interactions.

Automated summary

Cavity build up dispersion spectroscopy is a new technique that improves measurement speed and reduces sensitivity to detector nonlinearity in cavity-enhanced spectroscopy. It enables accurate measurements of dispersive frequency shifts, contributing to the validation of quantum theory and engineering of ultracold chemistry.