A clock apparatus with: (i) a gas cell, including a continuous path cavity including a sealed interior for providing a signal waveguide; (ii) an apparatus for providing an electromagnetic wave to travel along the continuous path cavity and for circulating around the continuous path cavity back toward and past a point of entry of the electromagnetic wave in the continuous path cavity; (iii) a dipolar gas inside the sealed interior of the cavity; and (iv) receiving apparatus for detecting an amount of energy in the electromagnetic wave, wherein the amount of energy is responsive to an amount of absorption of the electromagnetic wave as the electromagnetic wave passes through the dipolar gas.