The formation of quasi-nondiffracting focused beams with second-harmonic generation of flower Laguerre-Gaussian modes

We theoretically demonstrate that the second-harmonic generation of a flower Laguerre-Gaussian mode can be exploited to form a quasi-nondiffracting focused beam. It is verified that the product of donut Laguerre-Gaussian modes with opposite topological charges leads to the formation of the quasi-nondiffracting focused beam. The divergence of the quasi-nondiffracting focused beam is numerically confirmed to be root 2l + 1 times less than that of the Gaussian TEM00 mode with the same beam waist parameter, where l is the azimuthal index of the flower Laguerre-Gaussian mode. In an experiment, we employ a diode-pumped solid-state laser resonator with intracavity second-harmonic generation to realize the formation of the quasi-nondiffracting focused beams.