PDF《Cold beam of isotopically pure Yb》

28 MHz implies a large Doppler-cooling temperature of

690 ?K, it allows for Zeeman slowing over a short distance. The saturation intensity for this transi- tion is

58 mW/cm2 . Two of the nearby triplet-D states are lower in energy than the

1 P1 state, so the transition is not really closed, but the branching ratio of 10?7 to these states is negligibly small [12]. For example, the number of photons required to slow an atom from

300 m/s to

25 m/s is less than

105 . The two isotopes used in this study are

174 Yb (boson with I = 0), and

171 Yb (fermion with I = 1/2). Therefore, the isotope

174 Yb has a single hyper?ne transition from F =

0 → F′ = 1. The other isotope

171 Yb has two transitions: F = 1/2 → F′ = 1/2 and F = 1/2 → F′ = 3/2. The Zeeman shifts for the

0 →

1 transition in

174 Yb and the 1/2 → 3/2 transition in

171 Yb both have the same value of 1.4 MHz/G, hence the same Zeeman-slower pro?le and the slower-beam de- tuning can be used for both isotopes. The main laser for accessing the

399 nm transition is generated in a two-step process. We start with a single- frequency Ti:sapphire laser (Coherent 899?21) operating at

798 nm, pumped with

532 nm light (Spectra Physics Millennia X). Its output is frequency doubled to

399 nm in an external-cavity doubler with a lithium triborate crystal (Laser Analytical Systems), with conversion e?- ciency of about 12%. The output of the doubler is split into three parts: the ?rst part for the Zeeman-slowing beam, the second part for the 1D-molasses beams, and the third part to monitor its frequency in the ?uores- cence spectroscopy setup show........