Frequency measurements of transitions from the 2 P2 3 state to the 5 D2 1, 5 S1 3, and 5 D 3 states in ultracold helium

We perform laser absorption spectroscopy with ultracold He4 atoms to measure the energy intervals between the 2P23 level and five levels in the n=5 manifold. The laser light perturbs the cold atomic cloud during the production of Bose-Einstein condensates and decreases the phase space density, causing a measurable decrease in the number of atoms in the final condensate. We improve on the precision of previous measurements by at least an order of magnitude, and report an observation of the spin-forbidden 2P23-5D21 transition in helium. Theoretical transition energies agree with the observed values within our experimental uncertainty.