Fiber-Based Optical Gun for Particle Shooting

We proposed and fabricated a fiber-based optical gun for both particle trapping and shooting. The all-fiber device is made of a coaxial core optical fiber with a center core and a coaxial circular core. The fiber has a cone-frustum-shaped tip to enable the circular core to generate a focused ring light as a trapping beam, providing a stable 3D trapping potential well. When a small particle is trapped, a Gaussian beam is launched as a shooting light at the fiber center core to push the particle away from the fiber tip along the propagation direction of the beam. Here, we find that (1) the highly focused ring field with considerably lowered focusing intensity can generate a very stable particle-trapping potential well in three dimensions and the photothermal effect is also greatly reduced due to the lower optical power requirement for trapping and (2) the shooting light with a Gaussian profile not only supplies a radiation pushing force on the small particle, but also has restrictions and guiding effects as a gun barrel to propel the small particle out of the trapping well at a high speed along the beam propagation direction. The particle shooting distance can reach several hundreds of micrometers. Transverse deviation from the optical axis can be controlled within several micrometers under disturbances of ambient fluid flow. Our proposed method extends the potential applications of fiber-based optical manipulation, e.g., microparticle sorting in biology, accurate delivery of microparticles of a drug to the target cells, and observation of drug synergism.