Controllable spatial array of optical needles with independent axial intensity distributions for laser microprocessing

Abstract

Due to their high length to width ratio nondiffracting beams are usually perceived as “optical needles”. We construct an “optical needle” with an arbitrary longitudinal intensity distribution and change the spatial position of it in the focal region of a lens. Next, we introduce a spatial array of independent “optical needles” and report on physical limitations due to mutual interference of individual beams. We employ a spatial light modulator as a toy model of an actual geometrical phase element and experimentally observe controllable spatial arrays with various numbers and spatial separations of individual beam. Lastly, we examine the distortions caused by propagation through planar air-dielectric interface and attempt to compensate it.