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CHAPTER 3. EXPERIMENTAL SETUP
Figure 3.17: Two images of the MOT. On the left a normal MOT with 2·10 9
atoms, on the right side a compressed MOT, with 9 · 10 8 atoms left. The
images show the same area. One can see that the CMOT is at a different
position than the MOT, as described in section 3.4. The images are taken
with a detuning of the probe laser of -10 MHz to reduce the absorption,
otherwise the center of the cloud would be saturated.
detuning from the resonance. Special care has to be taken not to saturate
the atoms: once the intensity reaches the order of the saturation intensity,
the atoms absorb less photons, leading to a seemingly lower density. As
a MOT usually has optical densities too high to be measured with the
camera, we usually detune the lasers until saturation is sufficiently low.
Figure 3.17 show examples of the MOT imaging.
3.8 Computer control
The whole experiment is controlled by an MS-DOS PC running a program
written in Turbo Pascal. It commands an IO card which is multiplexed
over a bus connected to two types of output boxes: a digital
version with 16 outputs and an analog version containing 16 bit digital/analog
converters. They had five address bits which we increased to
six in order to double the number of boxes that can be connected.
Several other equipments are connected via a General Purpose
Interface Bus (GPIB, IEEE754) namely the radio frequency generators,
the function generator to generate the imaging pulses and a pulse
generator.
Over the years, the computer control had grown chaotic to a point
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