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.

超高保真吸收光谱的测量可以帮助验证量子理论，设计超冷化学和遥感大气。使用基于频率的色散或基于时间的吸收方法在腔增强光谱学方面的最新成就为精确度设定了新的记录，其不确定性低于亚密耳。但是，激光扫描或对非线性的敏感性限制了它们的最终性能。在此，我们以探测CO分子为例，介绍腔累积色散光谱（CBDS），其中腔共振的色散频移编码为腔对锁相非共振激光激发的瞬态响应。累积期间光频率之间的跳动精确地定位了与模式中心的失谐，因此可以进行单发色散测量。CBDS的准确度受到所选频率标准和测量持续时间的限制，与基于强度的方法相比，当前的检测非线性敏感性降低了50倍。而且，CBDS比以前的基于频率的腔增强方法要快得多。CBDS的普遍性显示出有望改善对各种光-物质相互作用的基础研究。