Owing to its peculiar non-diffraction, self-acceleration, and self-healing properties, Airy beam has attracted a great deal of attentions in various fields such as micro-manipulation, plasma generation, and optical microscopy. Now existing methods for generating nonlinear Airy beams are based on domain structure, nonlinear Raman-Nath diffraction, metasurfaces, and cylindrical lenses. Traditional methods usually have some disadvantages for generating nonlinear Airy beams, such as large size, low nonlinear generation efficiency, and difficulty of integration and fabrication.

Figure 1. Characterization of continuous cubic phase structure fabricated by FIB.

Figure 2. Observation of SH Airy beam.

We employ a 5 mol. % MgO: LiNbO3 (LN) nonlinear crystal as our sample, whose angle between the propagation direction and optical axis of the nonlinear crystal is 75 degree to satisfy the Type-I (oo-e) phase matching condition for 1064 nm fundamental frequency (FF) wavelength. The cubic phase pattern is shown in Figure 1a. The corresponding height of the designed structure is illustrated in Figure 1b when fabricating with FIB. The surface morphology of the nonlinear crystal recorded by scanning electron microscopy (SEM) is displayed in Figure 1c. Figure 1d is the locally magnified micrograph of Figure 1c. We also extract the height profile along diagonal direction marked with arrow in Figure 1b by an atomic force microscopy (AFM). The experimental setup to characterize the generated SH Airy beams is shown in Figure 2a. Figure 2b and 2c are, respectively, illustrate the theoretical and experimental results of SH Airy beam generated at the Fourier plane (z=0 um). We also present a three-dimensional representation of Figure 2c in Figure 2d. The normalized intensity distributions of the Airy beams along horizontal, vertical, and diagonal directions are shown in Figures 2e-2g, respectively. The normalized conversion efficiency is about (1.44*10^-5)%W^-1.

Figure 3. Transverse acceleration of generated SH Airy beam as a function of propagation distance.

Figure 4. Self-healing property of the SH Airy beam.

We also demonstrate the self-acceleration and self-healing properties of generated SH Airy beams. We record the intensity distributions and positions of the main lobe of generated SH Airy beams at intervals of 5 um of propagation distance. We can see that the generated SH Airy beam travels along a parabolic trajectory. We insert a needle into the light path to block the main lobe at z0=0 um shown in Figure 2a. From Figure 4d, we find that the SH Airy beam does not have a main lobe and persists undistorted at z1=10 um. With propagation, the main lobe regained most of its spatial intensity distribution at a propagation distance of z2=50 um. And at z3=100 um, the SH Airy beam self-heals and reconstructs its main lobe, which are in well agreement with theoretical simulations.

This work is published in “Qian Yang, Xiaona Ye, Haigang Liu, and Xianfeng Chen, Highly Efficient and Integrated Nonlinear Airy Beams Generation, Advanced Optical Materials, 2401810 (2024)”.