Optical dipole trap for a caesium Bose-Einstein condensate

Abstract

The scattering properties of Caesium, notably the tunability of its scattering length via magnetically induced Feshbach resonances, make it a promising candidate for improving the phase sensitivity in BEC matter wave interferometry but also require the use of a trapping scheme not reliant on magnetic fields. In this thesis the design, building and characterization of the experimental setup for a optical dipole trap on a atomchip in a very compact setup using a commercial self contained UHV chamber by ColdQuanta is presented. The trap will be used for the creation of a caesium Bose Einstein condensate as a matter-wave source for further experimental directions. The trap consists of two laser beams with a wavelength of 1064 nm, focussed to a 50 m waist and crossed orthogonally. The beams are detuned by 80 MHz up and down to eliminate interference effects disturbing the atoms. The laser power P can be continuously adjusted from 0 up to 6 W per beam, limited by the damage threshold of the mirrors on the atomchip yielding theoretical trap depths up to 450 K. The scattering rate per atom at the point of highest intensity is given by = P x 0,8207 Hz. The beam quality of the trapping beam has been characterized by a measurement of the M2 value M2 = 1:05. Temperature stability in the lab was found to be the main contributor to laser power instability with power fluctuating up to 10% for temperature drifts of about 3 C. Trap geometry under the influence of gravity and resulting trap frequencies were simulated. It will further be presented how the experiment was set up, including safety precautions and thermal management and a further outlook on the experiment will be given.