(a) Defined local coordinate system where X is along the lattice laser. (b) Differences of the temperature gradients near the cold atoms where the convection is uniform or not. The solid lines represent that the heat convection is uniform with the convective heat transfer coefficient of 100 W/(m²·K). The dash lines represent that the heat convections are inhomogeneous with the convective heat transfer coefficients of 13 W/(m²·K) and 200 W/(m²·K), respectively.