\pm 2$ sublevels. There are two additional peaks appearing outside the spectrum to the left, which are closer because of the smaller hyperfine intervals. The beam powers are 9 $\mu$W (probe) and 15 $\mu$W (pump).

Hyperfine measurements using an acousto-optic modulator
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The above experiments were done using separate pump and probe lasers. However, it is possible to do the experiment with just one laser by using an AOM to produce the scanning pump beam. The scan range of an AOM is limited to about 20 MHz, but this is large enough to scan across a hyperfine peak. The main advantage of using an AOM is that the frequency-scan axis (with respect to the probe beam) is both linear and calibrated by the rf frequency of the driver powering the AOM, thus allowing the hyperfine interval to be measured accurately. By measuring the entire peak, potential systematic errors due to locking of the pump laser to a peak are avoided. In addition, if there is a systematic shift in the lock point of the probe laser, this will not cause an error in the interval because the frequency which brings the pump into resonance will also be shifted by the 