Standing quasi-diffraction-free beams generated by circular Dammann gratings under high-order radially polarized Laguerre–Gaussian incidence

A standing quasi-diffraction-free beam generated by one-order cosine circular Dammann gratings is demonstrated in a single-objective 4Pi focusing system for high-order radially polarized Laguerre–Gaussian incident beams. Numerical results indicate that, similar to a Bessel beam, this standing quasi-diffraction-free beam can also well reconstruct itself after an obstruction, and the self-healing property implies that such beam should be more resistant to scattering. Furthermore, it is shown that, for a focusing system with a water-immersion NA=1.2 objective, the transverse and axial average sizes are about 0.43–0.54λ and 0.36–0.46λ, respectively, for those isotropic focus spots within the whole nondiffracting extent. It suggests that such standing quasi-diffraction-free beam can provide high resolving power along both transverse and axial directions when it is used as the excitation light in fluorescent microscopy. Therefore, this kind of standing quasi-diffraction-free beams should be of high interest in optical biological imaging and also parallel multiplane optical manipulation.