Simulation of Decelerating Metastable Hydrogen with the Bichromatic Force

Many important measurements of atomic hydrogen's structure (for example the 1S-2S transition) are currently limited by velocity-related uncertainties like transit-time broadening and second-order Doppler shifts. Laser cooling a hydrogen beam below 4 K cryogenic temperatures will enable unprecedented measurement precision to be achieved. Independent of our Lyman-α laser cooling pursuits, we here point out the two color bichromatic force is a feasible alternative method to decelerate the atoms when specific 2S-nP Balmer transitions are used. The bichromatic force facilitates momentum exchange entirely with absorption and stimulated emission, thus it is possible to use a transition that is not closed (like a Balmer line), so long as deceleration is accomplished before spontaneous emission from the nP excited state occurs. The Balmer-ε (2S-7P) and higher lines have this rare feature, and the ≈1 m/s recoil velocity implies 10² m/s deceleration should be possible. We employ a three-state model to simulate the force on a beam of cryogenic atoms which reveals deceleration and compression of velocity space on ∼100 ns time scales.