Near-diffraction-limited dark hollow beam generated by using a hybrid control way

We propose and demonstrate the generation of dark hollow beam with plane wavefront in the near field based on a hybrid control way by using dual phase only liquid crystal spatial light modulators (LC-SLMs). One phase only LC-SLM redistributes the intensity to the target distribution based on refractive beam shaping system and the other phase only LC-SLM adaptively compensates the wavefront of the output beam by using stochastic parallel gradient descent (SPGD) algorithm. Compared with conventional refractive beam shaping system, the hybrid control way can not only improve the far-field energy concentration of the output beam, but also can correct the phase distortion of the system. Influences of phase distortion on laser beam shaping are analyzed in detail. The theoretical and experimental results show that the near-diffraction-limited dark hollow beam can be successfully generated by using this hybrid control way. The power in the main lobe of the airy disk pattern area in the far field is 2.3 times larger than that without being adaptively compensated.