INTRINSIC SPECKLE NOISE IN IN-LINE PARTICLE HOLOGRAPHY

In-line holography of particle fields suffers from image deterioration caused by intrinsic speckle noise. This is not accounted for by previ ous theoretical treatments based on the scattering of a single particl e, nor has there been any quantitative description of this noise excep t for an empirical criterion by Royer [Nouv. Rev. Opt. 5, 87 (1974)] b ased on geometrical obscuration. We develop a theoretical model for in -line holography of multiple particles, using diffraction theory and s tatistical analysis, and show that the virtual image of the particle e nsemble is the dominant source of speckle in reconstruction. We quanti fy the effect of speckle with a signal-to-noise ratio (SNR). The SNR i s found to depend on a speckle parameter (which embodies particle diam eter, concentration, and sample depth) and on the film gamma. Experime ntal results show reasonably good agreement with our model. The SNR eq uation provides prediction of image quality and thence application lim its of in-line holography for particle fields. The fundamental underst anding obtained here points not only to constraints but also to possib le improvements in experimental procedures.