same amount, and hence the AOM offset (with respect to the probe) for the spectrum will remain the same.

We have therefore used a single laser and a scanning AOM to measure hyperfine intervals in the $D_2$ lines of Rb and Cs. The measurements are motivated by the fact that there are several experimental values reported in the literature that are somewhat discrepant from each other. In many cases, we feel that a potential source of error is the uncertainty in locking to a peak. In our current technique, measuring the entire spectrum avoids such errors, as discussed before.

The experimental schematic for this second set of experiments is shown in Fig. \[schema2\]. As before, the primary laser is a frequency-stabilized diode laser. The probe beam is derived after locking the laser to a hyperfine transition using SAS. The scanning pump beam is frequency offset from the probe using a double-passed AOM. The frequency is adjusted so that the pump is resonant with a nearby hyperfine transition whose interval has to be measured. The pump intensity is stabilized to better than 1% in a servo-loop by controlling the rf power driving the AOM. The two beams co-propagate through a vapor 