Particle Measurement using Holography

Abstract

　　　This review paper provides particle measurements using holography as a guide for the beginner. Especially, phase retrieval holography with two high-speed cameras is explained by comparing with conventional Gabor holography. Additionally, we introduce a graphic processing unit (GPU) acceleration to reconstruct holograms. Conventional holography has two problems: the twin image problem and reconstructed particle elongation. The first problem causes blurred and low contrast particles due to the lack of phase information. Phase retrieval holography can resolve this problem with several holograms recorded at different positions. The particle elongation is that a spherical particle is elongated in the optical axis in the reconstructed process. The elongation is proportional to the relationship between particle diameter and the wavelength of recording hologram. This relationship can precisely measure the microparticle diameter more than the measured diameter in the recorded plane with low resolution. This review paper demonstrates the observation of the three-dimensional trajectory of microdroplet and measurement of droplet diameter with the elongation using phase retrieval holography.