During the exploration of nonlinear crystal, such as BaMgF4 crystal for all-solid-state laser in the vacuum ultraviolet region, many problems emerged in the scattering centers caused by immature crystal-growth technology, which may bring difficulties to the periodic poling process for quasi-phase-matching.

In this paper, a random nonlinear process was observed only when the fundamental wave is illuminated onto the scratch of the BaMgF4 nanocrystal powder film. Then, the second-harmonic waves scattered from the nonlinear turbid media are re-collected to forward direction using feedback wavefront shaping. Using this method based on the genetic algorithm, the SH signal was focused to a bright point. The enhancement factor at the focused location was approximately 30 after 300 generations.

This work provides a repeatable way to increase the conversion efficiency based on the random nonlinear material. The experiment is also expected to be repeated in BMF nanocrystal ceramic, which can improve the SHG conversion efficiency towards VUV.