Coherent femtosecond x-ray pulses generated by X-ray Free Electron Lasers (XFEL) opened an avenue for studies structural morphology of biological systems with unprecedented sub-nanometer resolution. Serial coherent x-ray diffraction crystallography using XFEL requires a rapid non-contact high-precision injection method to deliver sub-micron particles into the x-ray focus volume of a few µm3. Current sample delivery systems based on aerodynamic focusing have extremely low sample delivery efficiency and low hit rate, which make bio-particle imaging experiments overly time consuming if not completely infeasible.

To address this crucial issue we designed an optical funnel based on a quasi-Bessel Beam for concentration of the particle beam and guiding particles to the desired location. The cross-section of the hollow-core optical funnel is down to a micron-scale while propagating, with controlled divergence, over several tens of millimeters. We applied the optical funnel to a stream of ~300 nm granuloviruses to demonstrate a four-fold increase of particle density in the x-ray focus, which converts into four times deduction of the sample consumption and data acquisition time. Control over the beam size, divergence and intensity distribution in the optical funnel will allow one to deliver single sub-micron size particles on demand, such as protein macromolecules, viruses and nanoparticles, into the XFEL interaction region for femtosecond diffractive imaging experiments.