Fresnel Hologram Calculation Method

Digital holography,with high precision, high sensitivity and non-destruction,is a novel optics branch compound of conventional optical holography and computer technology. Digital real-time holography which uses CCD or CMOS to record the holographic interference fringes which can be stored in the computer instead of traditional holographic plate, then people can reconstruct object's image by computer programming to detect the changing process of objects in real-time.Digital holography can record and reconstruct the amplitude and phase of object, which is especially good for the analysis and measurement of the object surface topography and is paid extensive attention by researchers around the world.Fresnel diffraction distribution can be simulated accurately by means of fast Fourier transform (FFT). Fresnel diffraction calculation plays a very important role in the study of digital holography, so it is applied widely to numerical reconstruction. However, Fresnel diffraction calculation based on FFT has to be satisfied certain conditions so as to obtain correct result. These conditions, such as a pair of planes vertical to optical axis, sampling center located at the optical axis, sampling interval limited by the distance between input and output planes, have confined the diffraction n simulation.Starting with Fresnel integral in form of convolution, a quick algorithm to simulate Fresnel diffraction is presented in the paper. According to this method, the limitation imposed on conventional Fresnel diffraction calculation can be removed. It is very helpful for numerical reconstruction in digital holography.