Ultra stable frequency references such as the ones used in optical atomic clocks and for
quantum metrology may be obtained by stabilizing a laser to an optical cavity that is stable over time.
State-of-the-art frequency references are constructed in this way, but their stabilities are currently limited
by thermally induced length fluctuations in the reference cavity. Several alternative approaches using the
potential for frequency discriminating of highly forbidden narrow atomic transitions have been proposed in,
e.g., [1] and [2]. In this proceeding we will present some of the ongoing experimental efforts derived from
these proposals, to use cavity-enhanced interaction with atomic 88Sr samples as a frequency reference for
laser stabilization. Such systems can be realized using both passive and active approaches where either the
atomic phase response is used as an error signal, or the narrow atomic transition itself is used as a source
for a spectrally pure laser. Both approaches shows the promise of being able to compete with the current
state of the art in stable lasers and have similar limitations on their ultimately achievable linewidths [1, 2].