check for errors that might depend on which direction the rf generator is scanned. Another source of error is whether the intensity stabilization servo-loop stays locked. But if this loses lock, it shows up in the spectrum as an asymmetry of the line shape. Indeed, both the sources of error discussed above also show up as asymmetry of the line shape. Thus a symmetric line shape is a good indication that the measurement proceeded correctly. From the residual asymmetry, we estimate the systematic errors to be 20 kHz.

Measurements in the $5P_{3/2}$ state of $^{87}$Rb
-------------------------------------------------

The first set of measurements were done in $^{87}$Rb. The different values in the literature are consistent with each other, and have an accuracy of 10 kHz. Therefore, our main motivation was to see if the scanning-AOM technique worked well and our error budget was proper.

A typical spectrum with the probe locked to the $F=2
\rightarrow F'=3$ transition and pump scanning across the $F=2 \rightarrow F'=2$ transition is shown in Fig.\[rb22\]. We saw earlier that the line shape was well described by a Lorentzian. We therefore fit a Lorentzian curve to the spectrum and extract the peak center. Note the symmetry of the 