Fig. 1. (a) Schematic of experimental setup. A cold atomic cloud interacts with a red-detuned Gaussian beam under gravity. A probe beam propagates along the y-axis for the absorption images. (b) A side view of the experiment.

Fig. 2. Experimental results of cold atomic clouds passing through a Gaussian laser beam. (a)−(c) Images of atomic clouds flying 7, 9, and 13 ms after passing through the Gaussian beam, respectively. (d) The black, red, and blue lines are the cross curve of the optical depths of (a)−(c) along the x-axis at the widest part of the atomic clouds.

Fig. 3. Experimental results. (a) The atomic cloud ballistically expands 16 ms after being released from the QUIC trap. (b)−(d) Images of atomic clouds flying 1, 5, and 9 ms after passing through the Gaussian beam, respectively.

Fig. 4. (a) and (b) Cross curves of the optical depths in Figs. 3(c) and 3(d) (black lines) and numerical simulations (red lines).