In this thesis we presented the way to align the collimator, and to optimise the cooling of the transverse velocity of the He* atoms with the collimator to create a parallel beam.
We measured the increase of the signal due to the collimator, and found a factor 2 of signal increase, which means about a factor of 3 increase in the number of He* atoms. We then have measured the velocity selective behavior of the collimator, both by examining the change of mean speed of the collimated atoms and by measuring the change in velocity spread at different detunings of the collimator laser. It was seen that a larger detuning to the red led to a higher mean spread of the He* atoms, varying from a mean speed of 920 m/s at a detuning of -100 MHz to a mean speed of 1280 m/s at a detuning of -150 MHz. For larger detunings the velocity spread of the He* atoms was larger, and converged to a value of 160 m/s to smaller detunings
To make sure that the measurements could be performed over a longer time range, we wanted to stabilize the laser frequency with use of two laser stabilization methods.We used saturation spectroscopy to stabilize the frequency of the MOC laser, and the beat signal between the collimator laser and the MOC laser to stabilize the frequency of the collimator laser with respect to the MOC laser frequency.
We have not yet measured the effect of the collimator working in combination with the MOC or the slowing laser. Since the collimator produces a beam with a width bigger than the sensitive surface of the channeltron, the increase of signal due to the collimator would be bigger if it was used in combination with the MOC, which compresses all He* atoms to a very thin parallel beam. Using the collimator in combination with the slowing laser could also increase the effect of the collimator. Since the atoms are slowed down by the slowing laser, and the transverse component of the atoms is unaltered by the slowing laser, the uncollimated atoms drift away from the central axis much faster than the collimated atoms. So the loss of signal due to the slowing is much smaller for the collimated atoms than for the uncollimated atoms.
If we use all three cooling devices, we can produce an intense, almost perfectly parallel beam of He* atoms with a speed that can be adjusted by changing the detuning of the slowing laser.
In the future this setup, with collimator, Zeeman slower and MOC, will be connected with the He* MOT (Magneto Optical Trap) setup with a Helium cooled source, which is described in ref [9] (see fig 4.1).
In this MOT we have He* atoms with a velocity very close to zero. If the two setups are aligned correctly, the well defined He* beam will hit the atoms in the MOT, and very exact collision experiments can be performed, since the velocity of the atoms in the MOT is zero, and the velocity of the atoms in the He* beam can be accurately prepared by adjusting the detuning of the slowing laser.
