We succeeded in trapping all the stable isotope of calcium (40Ca, 42Ca, 43Ca, 44Ca, 46Ca, and 48Ca) in our magneto-optical trap. The trap is loaded from a deflected, Zeeman slowed atomic beam. The deflection stage is an important step in decreasing the 40Ca background relative to the other isotopes. An important step in this experiment is the realization of single-atom counting. A lens system is inserted in the trapping chamber in order to collect as much fluorescence as possible. An essential step in reducing the background light level was painting the inside of the vacuum chamber black. Great care must be taken to suppress undesirable background light.
The trap has a temperature of a few milli-Kelvin, as is typical for alkali-earth MOTs. This corresponds to an average speed for the atoms of about half a meter per second. A picture (figure 2) is shown of the trapped calcium atoms. More close-up you can see picture 3. The picture is taken with a CCD camera. Figure 4 is just a fancy plot, showing the fluorescence intensity. At the moment the fluorescence of the MOT is recorded by a CCD camera, interfaced through a labview program. This enables us to subtract background light, average multiple images and change camera parameters in realtime.
We are also doing doppler free saturation absorption spectroscopy. This has been done in a small vacuum chamber that we have built that we use to stabilize the laser. A similar oven as the one connected to the MOT-chamber produces a beam of calcium atoms. Two counter-propagating laser beams of the same frequency are used to excite atoms in the beam. The laser beams are oriented perpendicular to the atom beam. We operate the oven at temperatures of up to 650 ˚C. We can clearly see the lamb-dip in the absorption signal (figure 5) and we observe doppler-free signals of the isotopes 40Ca, 42Ca, 43Ca, 44Ca and 48Ca. (figure 6).
As the laser frequency is scanned and we look at the MOT fluorescence with the CCD camera, we can see the different isotopes being trapped. This is shown in figures 8 and 9, below. We find that only the 9/2 component of 43Ca is trapped. The intensities of the trapped isotopes corresponds within a few percent to those listed in literature. Only from the 43Ca we trap less due to the hyperfine structure and the reduced Doppler fore.
|Last modified:||20 June 2014 10.19 a.m.|