Conclusion

On-line digital holography enables the position and properties of small objects (particles, drops, bubbles, etc.) contained in a volume to be measured instantaneously, from a single recording. Measurements and visualizations carried out using this technique always include a recording phase and a reconstruction phase. Optical setups are simple and robust, essentially consisting of a laser source shaped to illuminate the measurement volume and a matrix sensor (CCD, CMOS) placed opposite. The recording phase is akin to conventional image acquisition, while the reconstruction phase involves digital processing of the hologram. Numerous reconstruction methods exist. The most conventional consist of reconstructing images by backpropagation calculation in a discrete set of planes at different distances from the sensor. The stack of images thus reconstructed must then be analyzed to detect particles,...