  We create a spatially homogeneous field inside of a ring cavity by combining
two transverse modes generated by a single laser through modulation. The
interference term between the two modes averages out because of the frequency
difference between them, eliminating the need for interferometric control of
their relative phase. The use of a ring cavity allows for a large waist for the
flat-top profile, big enough to cover the atoms in an atomic trap. The cavity
is mechanically and thermally isolated, and the laser light is locked to the
cavity using the Pound-Drever-Hall technique. The flat-top profile technique
reported here fulfill the vanishing curvature criterion at the center of the
profile.
