Abstract

High-resolution spectroscopy on laser- trapped and cooled atoms has evolved into an effective tool for precision measurements and frequency standards research.¹ In these applications the achievable signal- to-noise ratio (S/N) is of crucial importance. The strong fluorescence on the cycling-trap transition is frequently used to monitor the small excitation rate on a much weaker clock transition (electron shelving and atom recycling).² In this case the change of the stationary-trap fluorescence rate is taken as a measure of the weak-line excitation probability. Because this fluorescence from the spatially-well-localized ensemble can be collected with high efficiency, the S/N is dominated mainly by the noise properties of the atom number, i.e., the atomic shot noise. The dynamics of the trapping process introduce long-term correlations into the fluctuations of the number of atoms. This leads to a nonwhite spectral density of the atomic shot noise. The correlations occur on time scales that are comparable to typical integration times during measurements. Therefore, the exact shape of the noise spectral density has to be taken into account when the S/N is determined.

© 1995 Optical Society of America