Non-diffracting optical quasi-Bessel beams provide an opportunity to construct optical fields of complex architecture. Theconstructed beams may have a bright central peak or zero intensity on the beam axis and have the beam size of only a fewmicrons propagating over a long defined distance, which is not possible with conventional Gaussian or high-order Laguerre-Gaussian beams. In this work we demonstrate the possibility of constructing a needle-like diverging optical funnel with zerointensity on the axis. The primary aim is to numerically construct and optimise the optical field, which could transverselycompress and focus a stream of m- and sub-m size particles injected into vacuum or gaseous environment by applyinglight pressure and photophoretic forces pushing particles into the area with lower intensity. We present the results ofnumerical modelling of an “optical funnel” based on re-imaging a non-zero-order quasi-Bessel beam, formed by an axiconand a phase plate or using an SLM, with a collimator. The funnel geometry, namely, the m-size of the beam cross-section,several-mm long propagation length and its divergence, all is controlled and optimised by changing the topological chargeat a fixed collimation of the re-imaging optics, or/and by varying the collimation with fixed topological charge of the beam.The simulated profiles will have an application for optical guiding and focusing of aerosolised beam of particles, largebiomolecules and viruses to the micron-size focus of x-ray Free Electron Lasers in order to increase the delivery efficiencyof isolated single particles in coherent diffractive imaging experiments.
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