FFT analysis method for pulse laser in-line hologram of small particles

This paper describes a novel idea of image analysis method of pulse laser in-line hologram of particles to obtain information on particle diameter. Present method is based on the following property of the hologram. Fringe interval of the hologram decreases with radius, and the corresponding spatial frequency increases with radius. Fourier transformed pattern of the hologram, therefore, has the similar properties. We have proposed here the use of this FFT pattern of the hologram for the image analysis. It is shown that the FFT pattern has a white ring zone, which corresponds to the zero-point of the envelope function of original fringe pattern. It is demonstrated that measurement of the diameter of this ring gives a reliable way of obtaining particle diameter. Feasibility of the method has been shown by numerical experiment for Fraunhofer and Fresnel hologram.