Volume Holographic Imaging For Optimal Design And Reconstructing Deep-resolved Images

The goals of traditional optical imaging systems are creating a projection of a3-D field onto a2-D receptor plane. Because of defocus, which is directly related tothe depth information, the image becomes blurred, and the information about thethird dimension is lost. No similar to the traditional optical imaging systems, volumeholographic imaging (VHI) is an imaging technique that exploits the Braggdiffraction selectivity of volume holographic gratings to optically slice the objectspace of the imaging system, and it can recover the entire3-D information about theobject. The information of an object is got slice by slice in volume holographicimaging system, in which the different slice is in correspondence to the differentposition, so it can get the altitude information for reflective objects and the refractiveindex for transparent objects. Therefore, volume holographic imaging has a brightfuture in medicine, military affairs and other fields.In this paper, firstly, based on the theory of volume holographic imaging andBragg diffraction selectivity of the holographic gratings, resolution characteristics ofvolume holographic imaging system are investigated. In the experiments, a volumehologram is recorded by two recording beams interfering at the wavelength of532nm. The grating recorded at wavelength of532nm can be Bragg matched at anotherwavelength of640nm by using a different reconstruction angle. The volumeholographic imaging with a white light is also conducted in the experiment. Theresult shows that more lateral information about the object can be obtained accordingto the Bragg degeneracy. The depth resolution of the volume holographic imagingsystem at different illumination sources are obtained experimentally, which is inaccordance with the theoretical value.Secondly, we add the microscope objective optics into the plane wave VHI, andtheoretically calculate the depth resolution, which is consistent with the experimentalvalue.Finally, two holographic gratings are recorded with angular multiplexingscheme in the same location of a Fe:Cu:LiNbO3crystal, and they are recorded withcollimated reference beam and signal beam at the wavelength of532nm. The effectof the image size, imaging location and the angle of the reference beam onreconstructing deep-resolved images are studied. The experimental resultsdemonstrate the ability of the VHI system to reconstruct depth resolved image oftinny object.