Absolute absorption line-shape measurements at the shot-noise limit

摘要

Here, we report a measurement scheme for determining an absorption profile with an accuracy imposed solelynby photon shot noise. We demonstrate the power of this technique by measuring the absorption of cesium vapornwith an uncertainty at the 2-ppm level. This extremely high signal-to-noise ratio allows us to directly observenthe homogeneous line-shape component of the spectral profile, even in the presence of Doppler broadening, bynmeasuring the spectral profile at a frequency detuning more than 200 natural linewidths from the line center. Wenthen use this tool to discover an optically induced broadening process that is quite distinct from the well-knownnpower broadening phenomenon.