Concave axicon (usually called negative axicon or concave cone lens) has an inward recessed central curved surface. Its main function is to diverge light rays. When parallel light is incident vertically, the concave axicon deflects light outward to form a divergent light cone. It can be used to generate hollow beams or annular light fields, which show great potential in applications such as micro-manipulation, atom optics, and particle trapping. For wavefront correction and aberration balancing, concave axicons can be combined with other optical components in complex optical systems (such as certain telescopes or microscopes) to compensate for spherical aberration or other aberrations, helping to improve final imaging quality.