Holography technique can be used to reconstruct the amplitude and phase information of an object. In the fields of optics, it is widely used in microscopy, optical tweezing, quantum information, and so on. We know that the more information of the holography technique can be reconstructed, the more vivid of the images compared to the objects in the real world. Therefore, all kinds of holography techniques are proposed in its development process. The 3D holography technique has attracted considerable public interest especially in field of holographic 3D displays, because it can be seen with the unassisted eye from different angles and is very similar to how humans see the actual environment surrounding them.

As we know, such holography realization is sensitive to the wavelength of the holography material. In most situations, the all-optical waveband realization of the holography technique is eager for the researchers to use it in different fields. One method to circumvent this problem is to develop the holography material, which satisfy different waveband requirement. However, this method needs to redesign the structure of the holography material with the changing of the laser wavelength and it is also hard to extend the wavelength scope of the holography realization once the holography material is determined. Nonlinear frequency conversion as the common method to extend the wavelength scope is naturally another way to realize this assignment. Until now, only 2D information of the nonlinear harmonic waves is generated and manipulated in all kinds of nonlinear holography processes mentioned above. Therefore, the real 3D holography is not still explored in the nonlinear optical process.

In this letter, we report the 3D nonlinear optical holograms for the first time as far as we know, which have high nonlinear conversion efficiency and dynamic property at the same time. To demonstrate its feasibility, the two-turn hollow helix pattern is well reconstructed in four imaging planes at first in our experiment. The letters “X”, “Y”, and “Z” (Fig.2) or the bird and rabbit can be well reconstructed simultaneously at different depth. The quality of the SH patterns has been analyzed, which demonstrates its reconstruction capability. The dynamic property is also manifested by the movie of a walking elephant and a wagging tail cat at different depth positions. In addition, we also calculate the normalized nonlinear conversion efficiency.

As we look forward with in the article, we can generate 3D optical holograms in arbitrary waveband by using different nonlinear frequency conversion processes in theory, such as sum-frequency and difference-frequency processes, which can efficiently extend the wavelength scope of such 3D holography without redesigning the structure of holography material. Besides, the dynamic property of our method can significantly increase the flexibility when such nonlinear 3D holograms are used in different areas. This study opens up the field of three-dimensional spatial nonlinear harmonic manipulation and may have the applications of all-optical waveband three-dimensional optical imaging, parallel micromachining, holographic displays, and so on.

Fig1. Schematic of realizing 3D nonlinear holography.  

Fig2. (a)–(c) show the profiles of the desired SH patterns corresponding to letters X, Y, and Z, respectively. (d)–(f) are the experimentally reconstructed SH patterns in their own imaging planes.

This research was published in “Yujia Wu, Haigang Liu, and Xianfeng Chen. Three-dimensional nonlinear optical holograms. Physical Review A 102, 063505 (2020)”

Link：https://link.aps.org/doi/10.1103/PhysRevA.102.063505