Generation of multiple optical needles using radiation pattern from sectional-uniform line source antenna

We present a method to produce multiple optical needles with variable lengths. The created needles are high purely longitudinal polarization and consistent beam size of ~0.36λ over two peak densities. This is achieved by inversing the electromagnetic field eradiated from a sectional-uniform line source antenna, for which the electric current is constant along each section, situated at the focus of the 4Pi focusing system. The required illumination distribution at the pupil plane to generate multiple optical needles can be obtained easily by solving the inverse problem. Numerical results indicate that the length of each needle is determined by the length of each sectional-uniform line source. These novel focusing patterns might found potential applications in particle acceleration, microscopy, and optical trapping.