Based on a new detection scheme, optical Ramsey fringes with a resolution of 4 kHz on the Mg 1S0‐3P1 intercombination line (λ=457 nm) have been detected using laser cooled and trapped atoms. Due to a pulsed excitation sequence, the signals are free from phase errors caused by the interacting laser fields and by the relativistic Doppler effect, resulting in an accuracy better than Δν/ν≊10−15. The influence of the electron shelving in the metastable 3P1 level on the trap dynamics is monitored on the fast and closed 1S0‐1P1 cooling transition (λ=285 nm). Simultaneously recorded Ramsey fringes on a thermal atomic beam allow a direct measurement of the second order Doppler shift.
Calcium ions are laser cooled in a Paul trap by use of a grating-stabilized UV laser diode. Unusual quantum jumps or fluctuations in the fluorescence signal are observed without application of any shelving lasers. It has become clear that such phenomena can be ascribed to shelving transitions induced by background 393-nm spontaneous photons emitted from the laser medium. Shelving transitions are suppressed by use of an interference filter, and the ions are successfully cooled to crystallization temperature with sufficient reproducibility.
We demonstrate here the direct observation of quantum jumps between the
62S1/2 state and the
52D5/2 state of an individual laser-cooled
Ba+ ions contained in a radio-frequency trap. The state detection and cooling are performed by two lasers which cause
62S1/2${\mathrm{\ensuremath{-}}6}^{2}$
P1/2${\mathrm{\ensuremath{-}}5}^{2}$
D3/2 transitions. Incoherent excitation to the
52D5/2 state (via the
62P3/2 level) causes the fluorescence from the
62P1/2 state to be suppressed for >30-sec lifetime of that state, after which the fluorescence reappears. The resulting ``telegraph signal'' provides a direct monitor of the atomic state.