This thesis presents work aimed towards achieving sideband cooling of 40Ca+ ions in
a Penning trap.
The observation of an increase in the number of quantum jumps as a function of the
trapping magnetic field is first presented. This observation is explained by the ion falling
into a long-lived D5/2 state, out of which the ion is not being re-pumped. The ion can fall
into this state due to mixing of the fine structure components with the same mJ quantum
number induced by the applied magnetic field. A calculation of the mixing and shelving
rate as a function of magnetic field strength is presented. This theory matches well with
the experimental results observed. This work has been presented in a publication in which
a perturbative analysis was used. An alternative analysis is presented here in which the
full Hamiltonian is diagonalised. The essential conclusions however remain unchanged.
This ‘J-state mixing’ effect means re-pumping from each of the six D5/2 state sub-levels
of our ion is required for efficient laser cooling. This is achieved by the addition of a system
comprising an 854 nm laser and a fibre EOM to provide the radiation required to re-pump
these levels. The same EOM is then used to re-pump out of the four sub-levels of the
D3/2 state using a single 866 nm laser. This is a great simplification of the experimental
setup required to cool a 40Ca+ ion in a Penning trap which would otherwise require ten
separate lasers to independently address each of the D sub-states.
Achieving efficient repumping leads to the ability to perform pulsed spectroscopy on
the quadrupole S1/2 → D5/2 transition in 40Ca+ . Preliminary results of this spectroscopy
in a radio-frequency trap are presented.