  We have shown earlier that hyperfine spectroscopy in a vapor cell using
co-propagating pump-probe beams has many advantages over the usual technique of
saturated-absorption spectroscopy using counter-propagating beams. The main
advantages are the absence of crossover resonances, the appearance of the
signal on a flat (Doppler-free) background, and the higher signal-to-noise
ratio of the primary peaks. Interaction with non-zero-velocity atoms causes
additional peaks, but only one of them appears within the primary spectrum. We
first illustrate the advantages of this technique for high-resolution
spectroscopy by studying the $D_2$ line of Rb. We then use an acousto-optic
modulator (AOM) for frequency calibration to make precise hyperfine-interval
measurements in the first excited $P_{3/2}$ state of $^{85,87}$Rb and
$^{133}$Cs.
