Two-photon absorption line profile of ions captured in a trap

The two-photon absorption line profile in a standing wave field is found for particles captured in a threedimensional trap. When the transverse dimension of the optical beam is comparable with the size of the trap, transit broadening is eliminated and the line profile is that of a resonance having the homogeneous width. For optical beams of small dimensions, homogeneous-width resonances occur in the line profile if the frequency of the ion oscillations in the trap is greater than the homogeneous width.