Pure-amplitude holograms for high-efficiency generation of phase radial grating based radial carpet beams: Theory and experiments under plane-wave and Gaussian illumination
This study introduces a pure-amplitude hologram (PAH) for generating radial carpet beams (RCBs), which are conventionally produced using pure phase radial gratings (PRGs). The hologram is designed by embedding the transmission function of a binary PRG into the phase argument of the cosine term(s) of an amplitude linear grating. When illuminated with a plane wave, this hologram generates RCBs in the non-zero diffraction orders, and when illuminated with a Gaussian beam, it generates RCB-like patterns at specific propagation distances. This method entirely eliminates the need for complex and expensive spatial light modulators (SLMs). The study presents a theory of diffraction for plane and Gaussian beams from such holograms, including a specific theoretical treatment of Gaussian beam diffraction from PRGs. Through theoretical analysis and experiments, we demonstrate how different RCBs can be generated at different diffraction orders due to the phase-amplitude enhancement resulting from multiplying the diffraction order number by the phase amplitude of the embedded base PRG, when the illuminating beam is a plane wave. For the Gaussian beam case, we show how different RCB-like patterns can be generated at different diffraction orders for the same reason, though only at specific propagation distances. Experimental and numerical results indicate that this technique yields RCBs and RCB-like patterns with approximately five times the useful power of their SLM-generated counterparts, demonstrating significantly higher power efficiency. This advantage renders the proposed method highly suitable for applications such as multiple optical trapping and free-space optical communication.