Tubular light beam with propagation-invariant diameter based on diffractive axicons

Abstract We present an optical system that generates from a Gaussian beam a ring-shaped light field with a propagation-invariant diameter. The system is implemented by combining two diffractive axicons with identical grating periods and is particularly suitable for applications in metrology, optical trapping, atom confinement, and laser material processing. Employing a binary structure for the first diffractive optical element enables the achievement of a truly tubular beam that is independent of the collimation state of the incoming laser beam. The design is analyzed through numerical simulations based on both geometrical and wave optics and is experimentally validated.