Optical frequency metrology with a Rb-stabilized ring-cavity resonator -- Study of cavity-dispersion errors

We have developed a technique to measure the absolute frequencies of optical transitions by using an evacuated Rb-stabilized ring-cavity resonator as a transfer cavity. We study possible wavelength-dependent errors due to dispersion at the cavity mirrors by measuring the frequency of the same transition in the $D_2$ line of Cs at three cavity lengths. We find no discernable change in values within our error of 30 kHz. Our values are consistent with measurements using the frequency-comb technique and have similar accuracy.