Research On Multi - Planar Digital Holographic Microscope Imaging

Multiplane digital holographic microscopy is a method of holography reconstruction which can obtain clear images of multiple planes simultaneously through once reconstruction on the base of digital holographic microscopy. Due to the restriction of the depth of field in digital holographic microscopy, there is only one image plane can be in focus. In this paper, we can get all in-focus images through one reconstruction at any distance in the condition of off-axis holography. The main content is as follows:1 Firstly the Fresnel diffraction theory is simply introduced here. Then off-axis holography is discussed. The diffraction light field of off-axis points is derived analytically and discussed. It is found that the diffraction light field of off-axis points is not only dependent on off-focus distance but also on recorded distance.2 The secondary diffraction is discussed in detail. The deduced result shows that the secondary diffraction field is the convolution of the first diffraction field, the pupil function of the second plane and the phase factor. The phase of the secondary diffraction field is adjusted by the phase factor. The deduction was also proved: the second diffraction is on the base of first diffraction.3 Several experiments of multiplane digital holographic microscopy are carried out in order to solve the problem of the depth of field and focus. The quadratic phase factor is utilized in the hologram to extend the depth in order to realize that all in-focus reconstructed images can be obtained in arbitrary distance through one reconstruction. Finally four clear images were obtained through this method. The results satisfied the theoretical predictions very well.