A
chip scale
atomic clock is disclosed that provides a low power atomic time / frequency reference that employs direct RF-interrogation on an end-state transition. The atomic time / frequency reference includes an alkali
vapor cell containing alkali atoms, preferably cesium atoms, flex circuits for physically supporting, heating, and thermally isolating the alkali
vapor cell, a
laser source for pumping alkali atoms within the alkali
vapor cell into an end
resonance state by applying an optical
signal along a first axis, a
photodetector for detecting a second optical
signal emanating from the alkali vapor
cell along the first axis, a pair of
RF excitation coils for applying an RF-interrogation
signal to the alkali atoms along a second axis perpendicular to the first axis, a pair of bias coils for applying a uniform DC
magnetic field along the first axis, and a pair of Zeeman coils for applying a Zeeman interrogation signal to the alkali atoms and oriented and configured to apply a time-varying
magnetic field along the second axis through the alkali vapor
cell. Another flex circuit is used for physically supporting the
laser source, for heating the
laser source, and for providing
thermal isolation of the
laser source. The
laser source can be a
vertical cavity surface emitting laser (VSCEL). The bias coils can be Helmholtz coils.