Analysis of Stimulated Forces for Slowing and Trapping Yb Atoms on the Narrow ¹S₀ ↔ ³P₁ Transition

Ytterbium based optical atomic clocks, degenerate gases, optical lattices, and tweezers for quantum measurements rely on Yb atoms cooled and trapped in a 556 nm MOT on the ¹S₀ ↔ ³P₁ transition. The conventional approach requires two stages of cooling to achieve a high loading rate and temperatures in the μK range and uses both the broad ¹S₀ ↔ ¹P₁ (399 nm, 28 MHz), and narrow (556 nm,182 kHz) transitions. To simplify the cooling and trapping system from using two lasers to one, we propose a method for slowing, cooling and trapping Yb atoms using stimulated forces and only the narrow ¹S₀ ↔ ³P₁ transition. 

We developed a computer simulation of stimulated slowing for a 2-level system, which describes well the closed transitions in Yb, and is applicable to other atoms (e.g. Ca, Sr, Mg). Our simulations include realistic experimental constraints (power, gaussian beams, geometry) and allow us to explore different approaches to optimize the loading rate of Yb atoms into a 556 nm MOT. We analyzed chirped detuning and broadband cooling to slow atoms over a 200 m/s velocity range and investigated the use of square amplitude modulation in comparison to a bichromatic standing wave field. With laser frequency chirp, our simulation predicts a loading rate of ~10⁸ atoms/s into a 556 nm MOT, comparable to that achieved using a 399 nm Zeeman slower. Preliminary results indicate that by combining AM and phase modulation the slowing force can be increased to at least twice the maximum achieved with bichromatic slowing.