Fourier transform detection of weak optical transitions with cyclic routines

Abstract

We demonstrate a means of detecting weak optical transitions in cold atoms that undergo cyclic routines with high sensitivity. The gain in sensitivity is made by probing atoms on alternate cycles leading to a regular modulation of the ground state atom population when at the resonance frequency. The atomic transition is identified by conducting a fast Fourier transform via algorithm or instrument. We find an enhancement of detection sensitivity compared to more conventional scanning methods of $\sim 20$ for the same sampling time, and can detect clock lines with fewer than $10^3$ atoms in a magneto-optical trap. We apply the method to the $(6s^2)$ ${}^1{S}_0-(6s6p)$ ${}^3{P}_0$ clock transition in ${}^{171}$Yb and ${}^{173}$Yb. The ac-Stark shift of this line in ${}^{171}$Yb is measured to be 0.19(3) kHz$\cdot$W${}^{-1}\cdot$m${}^2$ at 556 nm.

6 pages, 6 figures