Two-step Optical Excitation for Doppler Linewidth Reduction and Motion Study of Ions Stored in a Paul Trap

Abstract

Abstract Atomic thorium ions were stored in an r.f. quadrupole trap and excited by tunable laser light. One-step and two-step excitation schemes were applied; a four to eightfold reduction of the Doppler linewidth is obtained for the two-step scheme with essentially no loss in signal strength. The Doppler-free two-photon transition was also observed. The lineshapes were calculated using a simple model; the observed profiles were well reproduced proving that the velocity and acceleration features of stored ions are properly accounted for. A further reduction of the Doppler linewidth is expected for the two-step method if a short lived intermediate level is used.