Concave lens system of increasing Bessel beam non-diffracting distance

A new optical system to increase the Bessel beam's diffraction-free distance was designed and simulated based on traditional axicon method and geometric optical effects of concave lens. In the system, the concave lens was placed in front or in rear of the axicon. By simulating this program with Math CAD and comparing with traditional axicon method, some results were obtained that the diffraction free distance was increased from 244 to 638 mm, with central spot magnified when the concave was placed in front, and was increased to 406 mm when the concave was placed in rear. He-Ne laser was used as light source, the experimental results are consistent with the theoretical analysis and numerical simulation. Therefore, a certain curvature radius of the concave lens and the position according to actual requirements can be chosen to obatin the Bessel beam with a longer diffraction free distance and higher quality.