Size and shape measurement of microscopic powder particles using digital holographic tomography and 2.5D reconstruction

Size and shape are primary properties of microscopic powder particles and need to be measured and controlled to guarantee the function of the powder or the final product constructed with it. They are also important for the design and optimization of the manufacturing processes utilizing the powder. In this study, we demonstrate a method to estimate the size and shape of complex microparticles using digital holographic tomography (DHT), which can be applied to small microparticles lacking the absorption contrast to be utilized by other techniques. DHT allows for fast acquisition of the projection images for varying illumination angles. From the projection images, a diffraction-corrected thickness map can be synthesized, which can then produce the 3D envelope of the imaged specimen. Applying this method to polystyrene microspheres and two types of pharmaceutical powders with a size in the range of 5-100 mu m, we obtain various size and 3D shape parameters.