Arrangement for producing a Bessel beam
The invention relates to an arrangement for producing a Bessel beam ( 5 ), comprising a beam-forming element ( 2 ), which transforms a beam ( 1 ) incident as a plane electromagnetic wave into a Bessel beam ( 5 ). According to the invention, the beam-forming element ( 2 ) comprises at least one annular lens ( 3, 3 ′) and a Fourier optical unit, e.g. in the form of a Fourier lens ( 4 ).
1. An arrangement for producing a Bessel beam, comprising a beam-forming element, which transforms a beam incident as a plane electromagnetic wave into a Bessel beam,
wherein the beam-forming element comprises at least one annular lens;
a Fourier optical unit; and
a ring-shaped aperture that corresponds with the annular lens such that only ring-shaped radiation in the focus of the annular lens is transformed by the Fourier optical unit,
wherein the ring-shaped aperture is formed by a reflective or absorbent coating outside at least one convexly or concavely shaped annular region of the annular lens.
2. The arrangement according to claim 1 , wherein the Fourier optical unit is a Fourier lens.
3. The arrangement according to claim 2 , wherein the focal planes of the annular lens and of the Fourier lens coincide so that the annular lens and the Fourier lens form a Kepler configuration or a Galilei configuration.
4. The arrangement according to claim 2 , wherein the annular lens is configured in one piece with the Fourier lens so as to form a single, monolithic element.
5. The arrangement according to claim 1 , wherein the beam-forming element comprises two or more concentric annular lenses.
6. The arrangement according to claim 1 , further comprising a phase manipulating element arranged in the beam path which impresses a phase shift on the beam, said phase shift varying over the beam cross-section.
7. The arrangement according to claim 6 , wherein the phase manipulating element impresses a helical phase shift on the beam.
8. The arrangement according to claim 6 , wherein the phase manipulating element is a phase plate with a varying thickness in radial direction and/or peripheral direction relative to the beam axis.
9. The arrangement according to claim 1 , further comprising a beam pre-forming element arranged in the beam path upstream of the beam-forming element, said pre-forming element transforming the incident beam into a beam with a ring-shaped cross-section.
10. The arrangement according to claim 9 , wherein the beam pre-forming element comprises a concave axicon and a convex axicon arranged in the beam path downstream thereof.