Axialisation of laser-cooled calcium ions in a Penning trap
Prof. Richard Thompson (Imperial College, London)

Laser cooling provides a powerful means to reduce the kinetic energy of trapped atomic ions. However, in the Penning trap the cooling is complicated by the nature of the magnetron motion, which has a negative energy associated with it. As a result, the cooling is not as effective as it is for small numbers of ions in a Paul trap. Axialisation is a technique that can overcome this disadvantage by coupling the magnetron motion to the strongly-cooled cyclotron motion. I will present our studies of axialisation of small clouds of calcium ions. This species requires several lasers for laser cooling due to the need to address all Zeeman components of the laser cooling transitions in the strong magnetic field of the Penning trap. A theoretical treatment of axialisation including the effect of laser cooling allows us to predict the properties of the normal modes of the coupled system, and I will present our experimental measurements of the frequencies and damping coefficients of these modes from the phase response to a near-resonant driving field.