Non-paraxial pin-like optical beams: geometric design and pulling forces

We demonstrate non-paraxial pin-like optical beams and further report their mechanical features during their interactions with particles. These beams are designed by using a geometric method, followed by the discovered mechanism of their formation in terms of optical rays. They exhibit a progressively narrowing of their main intensity lobe along the propagation distance in the range of several micrometers. In momentum space, the phase of these beams is obtained via a correspondence between real and Fourier spaces, and the amplitude is found to preferably locate at higher spatial frequencies. Based on this angular spectral information, the longitudinal forces felt by particles placed in a pin-like optical beam imparted with radial polarizations are calculated, and pulling forces are found for specific particle size and propagation distance ranges.