Single-Atomic-Ensemble Dual-Wavelength Optical Standard

We demonstrate a dual-wavelength optical frequency standard based on the dual-optical-transition modulation transfer spectroscopy (DOT-MTS) between different quantum transitions of the rubidium D1 (795 nm) and D2 (780 nm) lines. In a single rubidium atomic ensemble, modulation frequency sidebands from the 780 nm pump beam are simultaneously transferred to both the 780 nm and 795 nm probe lasers. The DOT-MTS enables the simultaneous stabilization of 780 nm and 795 nm lasers on a single vapor cell. Both lasers exhibit a frequency instability in the low 10$^{-14}$ range at 1 s of averaging, as estimated from the residual error signal. A theoretical model is developed based on the V-type atomic level structure to illustrate the dual-wavelength spectroscopy. This approach can be extended to develop a multi-wavelength optical frequency standard within a single atomic ensemble, broadening its applicability in fields such as precision metrology, wavelength standards, optical networks, and beyond.