We analyze the feasibility of a cold 87Rb optical frequency standard based on the S-P-D transition in which two-color EIT laser cooling and interrogation are performed at 780 and 776 nm.
We demonstrate an optical frequency standard based on rubidium vapor loaded within a hollow-core photonic crystal fiber. We use the 5S(1/2)→5D(5/2) two-photon transition, excited with two lasers at 780 and 776 nm. The sum-frequency of these lasers is stabilized to this transition using modulation transfer spectroscopy, demonstrating a fractional frequency stability of 9.8×10(-12) at 1 s. The current performance limitations are presented, along with a path to improving the performance by an order of magnitude. This technique will deliver a compact, robust standard with potential applications in commercial and industrial environments.
Sr-atoms are of special interest for an optical frequency standard since a large number of atoms can be cooled down efficiently to ultra-low temperatures in a magneto-optical trap (MOT). The ultra-narrow line on the forbidden 1 S 0 -> 3 P 0 transition of 87 Sr ( 3 P 0 natural lifetime is approx. 100 s), and the ability to interrogate Sr atoms in a perturbation free dipole trap promise un-precedented low inaccuracy level and relative frequency instability, well below 10 -15 tau -1/2 . We will show the realization of an efficient atomic source of cold Sr atoms and the construction of an ultra-stable laser for the interrogation of the atoms.