A stereo-tweezer for ultracold atoms

Abstract

The Atom Plasmonics group plans to study the interactions between Rubidium atoms in the near-field of nanostructures. For these experiments an optical tweezer is needed to move the trapped atoms above a gold surface. To transfer the atoms to the surface, this tweezer must actually be a standing wave. Thus, a second tweezer should be overlapping with the first. This stereo tweezer or scanner will consist of two pairs of scanning mirrors that move the trapping beam in the plane above the surface. In this thesis the design and the performances of this stereo scanner in one dimension was tested. To implement the scanner, standard galvo scanning mirrors were used as is typically done in confocal scanning microscopy. However, two problems arise with the use of these galvos. First, the electronic feedback that controls the angle of the mirror, introduces noise in the angle and thus in the position of the trap. As a result, a bump arises in the spectrum of the noise. By tuning the constants of the controller of the galvos, this bump was decreased. Second, the two beams should remain overlapped even when the mirrors are scanning. This was achieved by measuring the difference in angle between the galvos and correcting the angle of one of them using a feedback loop. This method was tested by coupling light that has pasted over both galvos back into a single-mode fiber. If the feedback system works the light should remain coupled in the fiber even when the mirrors are scanning. Remaining fluctuations in the fiber coupling were found to be dominated by movements of the beam orthogonal to the scanning axis.