Probing quasi-2D condensates using $\it{in situ}$ and focusing imaging methods

A 2D interacting Bose gas in an infinite uniform system doesn't undergo Bose-Einstein condensation due to long-wavelength thermal fluctuations. Instead, a Berezinskii- Kosterlitz-Thouless (BKT) transition is predicted. The system goes from superfluid state to normal state by dissociating vortex and anti-vortex pairs when approaching the transition temperature from below. However, in a finite inhomogeneous quasi-2D system, the process of the transition coming from normal state to BEC state is still not clear. We report our latest results on probing quasi-2D condensates using two different imaging techniques, $\it{in situ}$ and focusing imaging. The $\it{in situ}$ imaging and the focusing imaging methods probe the quasi-2D gas in coordinate space and in momentum space respectively. The two distributions provide different crucial information about the properties of an interacting quasi-2D Bose gas in an inhomogeneous trapped system.