A clock apparatus, with: (i) a gas cell, including a cavity including a sealed interior for providing a signal waveguide; (ii) a first apparatus for providing a first electromagnetic wave to travel in the cavity and along a first direction; (iii) a second apparatus for providing a second electromagnetic wave to travel in the cavity and along a second direction opposite the first direction; (iv) a dipolar gas inside the sealed interior of the cavity; and (v) receiving apparatus for detecting an amount of energy in the second electromagnetic wave after the second electromagnetic wave passes through the dipolar gas.