In this work, we show that suitable continuous superposition of zero-order Bessel beams, combined with the use of a mathematical operator which raises the topological charge of any optical beam, allow us to structure on demand non-diffracting hollow beams endowed with orbital angular momentum (OAM) within micrometer spatial domains. Our Analysis is exact and analytical, fully based on the Maxwell equations. Such method can find potential applications in many fields, especially those which require the use of highly non-paraxial optical beams, like optical tweezers, optical guiding of atoms, control of the OAM over microscopic regions and photonics in general.
We experimentally demonstrate a class of non-diffracting beams with state of polarization (SoP) and intensity that can both be controlled along the propagation direction. The beams are composed of a superposition of equal frequency co-propagating Bessel beams (BBs) with different transverse and longitudinal wavenumbers. The BBs are weighted by suitable complex coefficients derived from closed-form analytic expressions. The desired polarization states (i.e., linear, radial, azimuthal and elliptical) are each independently encoded onto a set of BBs with the suitable polarizations. For experimental generation, the resulting field is decomposed into two orthogonal polarizations (horizontal and vertical). Via constructive (and destructive) interference of BBs, specific SoPs can be designed to switch on (and off) during propagation. This effectively alters the resultant SoP and intensity of the beam throughout propagation. We envision our proposed method to be of great interest in many applications, such as optical tweezers, atom guiding, material processing, microscopy, and optical communications.
We present an experimental demonstration of a class of beams, namely Frozen Waves, that can carry predetermined longitudinal intensity profiles in the presence of modeled loss. These waveforms consist of a superposition of equal frequency Bessel beams with different transverse and longitudinal wavenumbers, and are generated using a programmable spatial light modulator addressed by computer-generated hologram. Attenuation-resistant Frozen Waves can address challenges associated with light-matter interaction in absorbing media encountered in imaging, remote sensing, and particle micro-manipulation, to name a few.