High-aperture raster holography for particle imaging

A novel approach to in-line particle holography is described, and its superiority is experimentally demonstrated. During recording, a raster diffuser is used to increase the effective angular aperture of particle scattering, and a raster screen is placed in front of hologram to mask the unscattered diffuse light. In reconstruction, a new type of spatial filter passes only the spherical waves from the interrogation region, effectively blocking the reconstruction beam, separating the real and virtual images, and suppressing the strong forward scattering. This new scheme provides particle images with higher contrast, reduced speckle noise, and a smaller depth of focus than conventional in-line holography.