Van der Waals - Zeeman transitions of slow metastable argon atoms Ar*(³P₂)

Metastable argon atoms Ar*(³P₂), produced by electron bombardment of a nozzle beam of ground state Ar atoms, are slowed down from their initial thermal velocity of 560 m/s down to a few tens of m/s, using a standard Zeeman slower. In this decelerator [1], a repulsive force is induced by a counter-propagating ⁺-polarized laser beam, locked in frequency on the ³P₂-³D₃ closed transition ( = 811.5 nm) and then detuned by 340 MHz. A special profile of longitudinal magnetic field is adjusted in order to maintain atoms in resonance with light all over the device, by compensating the variable Doppler shift by the convenient Zeeman shift. Low velocities, e.g. 55 m/s, are accessible but due to spontaneous emission randomly distributed recoil momentums enlarge both angular and velocity distributions of the beam [2]. Nevertheless, by placing off axis collimating slits and grating, it is in principle possible to observe transmission and/or diffraction phenomena specific of low velocities.