Copyright by Kirsten Viering 2006 - Raizen Lab - The University of ...

the scattering rate in the MOT with the detuning ∆ = 20MHz of the MOT-beams and the
scattering rate in presence of the YAG-light with the total detuning ∆tot = ∆ + δ. Thus
the expected change in the fluorescence signal is about 2% relative to the flourescence
without the YAG-beam. Nevertheless, we were not able to detect a change in the
fluorescence signal.
The attempt to introduce a frequency modulation of the MOT-light itself using
two DDS (Direct Digital Synthesis) failed. The switching of the DDS resulted in tran-
sients that were picked up by the MOT fluorescence. Changing the frequency using
a frequency generator (HP 0.1-2010 GHz FG) with external modulation we succeeded
to induce a change in flourescence. At a modulation frequency of 10kHz we could
detect down to a 2kHz change in the MOT-frequency. The corresponding change in the
flourescence signal was 0.48%.
A stronger effect of the AC-Stark shift is expected at a wavelength of 532nm, far
away from a magic wavelength. Hence we followed the same experimental procedure
using a Verdi laser (Coherent Verdi V10) instead of the YAG-laser; but we still could
not detect a meaningful signal. It is possible that the changing magnetic field in the
MOT complicates the measurements in a way we were not considering.
In our future experiments we will not drive a clock transition, therefore we
are not obliged to use a magic wavelength. Moreover, since the atoms are in different
hyperfine states, a trap cannot be at a magic wavelength for all the atoms. Nevertheless,
it is advantageous to be near a magic wavelength to avoid a strong heating of the atoms.
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