  We present a technique for simultaneous laser frequency stabilization on
transitions of multiple atomic species with a single optical setup. The method
is based on modulation transfer spectroscopy and the signals are separated by
modulating at different frequencies and electronically filtered. As a proof of
concept, we demonstrate simultaneous spectroscopy of the potassium D$_1$, D$_2$
and rubidium D$_2$ transitions. The technique can easily be extended to other
atomic species and allows the development of versatile and compact frequency
reference modules.

Atomic Physics