Studies On Design And Fabricating Technology Of Diffractive Axicon

Diffraction-free Bessel beam has some optical characteristics of the extremely narrow central spot radius,without being subject to diffractive spreading,etc,these characteristics make diffraction-free Bessel beam receive the widespread attention in some areas of optical tweezers,nonlinear optics,laser alignment,etc.Traditional refractive axicon can produce the diffraction-free Bessel beam,but,compared with the traditional refractive axicon,diffractive axicon can also produce the diffraction-free Bessel beam,and diffractive axicon has some inherent merits of miniaturization,lightweight and integration,etc.Based on the traditional refractive axicon,a diffractive axicon is designed and analized,and it is also fabricated and tested in this paper.First,according to the phase function of the traditional refractive axicon,the phase function of the diffractive axicon with the maximum phase value 2? can be obtained by compressing phase,based on the theory of angular-spectrum,a theoretical analysis model of the diffractive axicon with the parallel Gaussian beam illumination is set up.The influence of the period width of the diffractive axicon and the waist radius and wavelength of incident Gaussian beam on the diffraction intensity distribution of the diffractive axicon is analyzed in detail.According to the research results,with the increase in the period width of the diffractive axicon,the center spot radius of the diffraction-free Bessel beam and the maximum non-diffraction distance is increasing,with the increase in the waist radius of the incident beam,the maximum non-diffraction distance is increasing,the maximum non-diffraction distance decreases with the increase of wavelength.Secondly,based on the phase function of the diffractive axicon,the two kinds of optical elements of helical axicon and array axicon is designed respectively,the mathematical model is set up respectively,the diffraction intensity distribution of the two kinds of optical elements with the monochromatic Gaussian beam illumination is analyzed.According to the research results,the order of the Bessel beam generated by the helical axicon is the same as topological charge,array axicon can generate an array of diffraction-free Bessel beam.Last,using a single-point diamond ultra-precision lathe to machine the designed diffractive axicon,the surface shape and the surface roughness of the diffractive axicon are measured by the detection of Stylus Profiler and White Light Interferometer,according to the testing results,the surface profile is basically consistent with the design value,the surface roughness is controlled within 4nm,the results verified the rationality of the processing parameter settings and tool parameter selection.