Paramagnetic particles in an optical trap

A setup based on an optical trap combined with homogeneous magnetic fields is presented. The system allows one to accurately control the alignment of multiple particles within the trap by controlling the external magnetic field. I study how two and three paramagnetic particles interact in the trap, and show that the experimental results can be explained in terms of dipolar interactions. It is also demonstrated that the system can be used to measure the magnetic moment of paramagnetic particles with a resolution of 10−15 Am2.