Double spiral phase filter digital in-line holography for particle field recording and tracking

The application of digital in-line holography in fluid velocimetry is mainly limited by the twin image that hinders the particle position and velocity measurements. In this work, we propose the use of two spiral phase filters in a digital in-line holography configuration to discriminate the real and virtual images. The first filter is a physical plate that modifies the object spectrum prior the recording. The second filter is a numerical frequency filter, applied in the reconstruction process, which reshape one of the particle images into a point-like image while blurs its twin image. In this way, particle tracking algorithms, based on the detection of intensity peaks, can easily locate and track particles. The good performance of double spiral phase filter in-line holography for particle field recording and particle tracking has been demonstrated experimentally in the present work. © 2024 The Authors