The storage time of Yb+ ions trapped in an r.f. trap was determined by the rf resonance absorption method in the presence of buffer gas, without and with laser radiation of a frequency equal to the transition from the S1/2 ground state to the excited P1/2 state. The storage time of the ions with the buffer gas (presure between 1 × 10−4 and 4·2 × 10−4 Pa) was several hours without the laser radiation; this period was shortened to several hundred seconds by irradiation with a 500 nW laser source. This phenomenon shows that the trapped Yb+ ions disappeared from the trap as a result of irradiation with the resonance laser light.
We report on a study to determine the efficiency of various buffer gases in quenching the population trapping states of laser excited ytterbium ions. The ions were confined in an rf/dc hybrid trap, and their /sup 2/S/sub 1/2//spl hArr//sup 2/P/sub 3/2/ transition was excited with 329 nm laser light. Buffer gases used include H/sub 2/, N/sub 2/, CO/sub 2/, Ar, and He at several different pressure regimes. We have identified N/sub 2/ to be highly efficient in quenching the population of the trapping states, and thus be the most suitable buffer gas to use with ytterbium for the development of a trapped ion microwave frequency standard.
It is known that fluorescence of trapped
Yb+ ions fades with continuous driving of the
2 S1/2${\mathrm{\ensuremath{-}}}^{2}$
P1/2 transition in the presence of buffer gases. This phenomenon has been interpreted as being caused by population trapping in the
2 F7/2 state of
Yb+ . As another cause of the fluorescence disappearance, we found the production of
YbH+ by chemical reaction of
Yb+ in excited states with
H2 gas. We found that the wavelengths of 369.482, 369.202, and 368.947 nm, formerly assigned as wavelengths for deexcitation of
Yb+ in the
2 F7/2 state to the
2 S1/2 ground state, are actually photodissociation lines of
YbH+ . The change of the resonance point of rf resonance absorption signals indicates the production and dissociation of
YbH+ ions. The production of
YbH+ may be a problem in establishing frequency standards using buffer-gas-cooled
Yb+ , owing to difficulty in removing
H2 gas from vacuum systems.