Flattening a trapped atomic gas using a programmable optical potential in a feedback loop
We present a method for producing a flat, large-area Fermi gas of $^6$Li with a uniform area density. The method uses a programmable optical potential within a feedback loop to flatten the in-plane trapping potential for atoms. The optical potential is generated using a laser beam, whose intensity profile is adjusted by a spatial light modulator and optimized through measurements of the density distribution of the sample. The resulting planar sample exhibits a uniform area density within a region of about 480 $\mu$m in diameter and the standard deviation of the trap bottom potential is estimated to be $\approx k_B \times$ 6.1 nK, which is less than 20$\%$ of the transverse confinement energy. We discuss a dimensional crossover toward 2D regime by reducing the number of atoms in the planar trap, including the effect of the spatial variation of the transverse trapping frequency in the large-area sample.