How can holography be used to measure the size of dust particles and liquid droplets?

Holography is used to determine the size distribution of dust particles and liquid droplets by transforming transient, moving events into stationary images for detailed evaluation. This application, which functions similarly to microscopy, relies on the principles of Fraunhofer holography.1

Because these particles are typically in motion, a hologram must be captured instantaneously to prevent blurring. To achieve this, a pulsed-ruby laser technique is employed. The hologram is formed by the interference between the light diffracted by the particles or droplets and the coherent background light that passes directly through the sample.1

Once the hologram is recorded, it can be illuminated by a coherent beam during reconstruction to produce a series of stationary images. These images allow researchers to examine the particles at their leisure, providing a precise method for measuring their size and distribution.1