Experimental generation of a flat-top beam profile in a stable ring cavity

Abstract

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.

Beam Shaping by Mode Superposition With Coefficient Optimization

“…Owing to the important potential applications of flat-top beams, their generation has attracted considerable attention [9][10][11]. Researchers have proposed several methods to produce flat-top beams, such as employing annular cavity structures [12], making aspheric lenses with 3D printing technology [13], implementing beam shaping inside the cavity [14], and utilizing axicons [15] or special diffraction optical elements [16]. Zhu et al utilized fiber-coupled semiconductor lasers as the light source and a beam homogenization system to achieve a flat-top beam output with a power of 1940W [17].…”