The computer-generated holography technique is a powerful tool for three-dimensional display, beam shaping, ultrashort pulse laser parallel processing, and optical encryption. Nowadays, computer-generated holographic imaging has been realized in various ways, including spatial light modulators (SLMs), metamaterials, and diffractive optical elements (DOEs) fabricated by laser or lithography. However, these ways achieved holographic imaging in the linear optics and had some limitations when applied to the nonlinear field. In recent years, the combination of nonlinear frequency conversion and wavefront shaping has been widely studied. In this Letter, we demonstrate a general approach to realize the nonlinear computer-generated holographic imaging by using femtosecond laser micromachining.

We have chosen two specific original images: “SJTU” and the Shanghai Jiao Tong University (SJTU) logo for experiments. We encoded these images with the detour phase method. The calculated computer-generated hologram (CGH) patterns were fabricated in LiNbO3 with 0 or +1 binary modulation of quadratic susceptibility by femtosecond laser micromachining, as shown in Figure (a). The modulated LiNbO3 crystal was cut for a specific angle between the optical axis and the z axis, where the phase-matching condition is fulfilled through birefringence phase matching (BPM) in the longitudinal direction. By sending a nanosecond laser of 1064 nm wavelength to the fabricated CGH, the bright SH holographic imaging can be achieved in the far-field.
Figure (b) shows the comparison between the experiment and simulation results of the SH holographic imaging. The ability to convert the frequency of light and generate holographic imaging simultaneously in a monolithic ferroelectric crystal will be useful for all-optical 3D displays and high power laser nonlinear holographic imaging fields.

Figure: (a) The fabrication of the CGH pattern by femtosecond laser micromachining. (b) The comparison between the experiment and simulation results of the SH holographic imaging.

This research was published in“Bing Zhu, Haigang Liu, Yi’an Liu, Xiongshuo Yan, Yuping Chen*, and Xianfeng Chen, Second-harmonic computer-generated holographic imaging through monolithic lithium niobate crystal by femtosecond laser micromachining, Opt. Lett. 45, 4132-4135 (2020)”

Link：https://doi.org/10.1364/OL.394162