Formation and evolution of ultracold plasma in a rubidium magneto-optical trap

We obtained ultracold plasma by the photoionization of laser cooled atoms, and by the spontaneous evolution of dense Rydberg atoms in a rubidium magneto-optical trap. Up to 10⁷ Rb atoms were trapped in the magneto-optical trap at temperature down to 500 μK, then a pulsed dye laser ionized or excited the cold Rb atoms, and the number of ions or Rydberg atoms was varied by the power of the pulsed laser. The dynamics of ultracold plasma was investigated by extracting the electrons from plasma using a delayed ramp or pulsed electric field. The experimental results were in good agreement with the Coulomb potential well model. Due to the contribution from the long-lived Rydberg atoms, the ultracold plasma from the spontaneous evolution of dense Rydberg atoms had a longer lifetime than that from the photoionization. (authors)