Ring-Shaped Bessel Beam based on Diffractive Axicon
A diffractive axicon converts a laser beam into a ring-shaped Bessel beam. Typically diffractive axicons have no influences on the ring beam's width. The beam width depends on the incident beam and focal lenses. Specifically, the width of the ring-shaped beam at a certain position is equal to half the beam's width when you take the diffractive axicon out from the optical path.
The main parameters of a diffractive axicon are the base angle α (also referred to as axicon angle) and wavelength λ. Obviously the relationship between base angle α and apex angle (also referred to as cone anlge) θ is
The half fan angle after a laser beam passes a diffractive axicon is:
where n is the refractive index of the material of diffractive axicon. Full fan angle (Ring angle, P2P）is twice the half fan angle, i.e.
The diameter of the ring is:
where L is the working distance.
| Item number | material | wavelength | refractive index | dimension | base angle | apex angle | half fan angle |
| AX-5p86mrad-10p6-25p4-p76deg | Gallium arsenide | 10600 nm | 3.27 | Φ28 mm | 5.86 mrad | 3.13rad | 0.7639 deg |
| AX-9p50mrad-10p6-25p4-p76deg | Zinc selenide | 10600 nm | 2.40 | Φ28 mm | 9.5 mrad | 3.12 rad | 0.7639 deg |
| AX-p1mrad-532-0p46mrad | Fused silica | 532 nm | 1.46 | Φ25.4 mm | 1 mrad | 3.1396 rad | 0.46 mrad |
| AX-p05mrad-532-p023mrad | Fused silica | 532 nm | 1.46 | Φ150 mm | 0.05 mrad | 3.1415 rad | 0.023 mrad |
