Digital in-line holography (DIH) combined with a Wiener filter has been applied to measure particle size and position in the flow inside a capillary model, seeded with magnetic particles (3µm) and with solid opaque particles that simulated red and white cells. The proposed filtering process takes advantage of the linearity implicit in the numerical reconstruction of the object complex amplitude. A modified DIH set-up, with a tilted illumination beam, was used as it presents two main advantages: it solves the twin image issue associated to in-line holography and increases the out-of-plane resolution. Experiments show that the proposed method discriminates particles within a range from 3 to 30µm with a sensitivity of 0.5µm. © 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

The three velocity components in a fluid plane can be measured by applying Digital Image Plane Holography. This technique is limited by the laser coherence length, which reduces its application with high speed lasers that, generally, have a very short coherence length. In addition, the use of a double cavity can also imply a small wavelength difference between the two laser beams. In this work, we present an improved Optical Path Length Enlarging Device that allows the velocity measurement, in a 2D field whose width is four times larger than the laser coherence length. The optical set-up and the procedure for measuring in a larger field (ten times the laser coherence length) were optimized, and the issues derived from the laser spatial and temporal coherence and wavelength changes were analyzed and solved. Digital Image Plane Holography with the Optical Path Length Enlarging Device and Particle Image Velocimetry were applied for measuring the whole velocity field in the central plane of a cylindrical cavity with a rotating lid, for two Reynolds numbers (800 and 2000), showing both of them a very good agreement with the numerical simulations.

In this work, we propose and validate the Image Plane Digital Holography (IPDH) with laminar illumination technique for measuring the complete coherence degree, the temporal coherence length and the spatial coherence area (transversal coherence radius), of a light source at the same time and from a single measurement. This holographic technique has been used before as a fluid velocimetry technique that allows measuring the three components of the fluid velocity in a plane. Since its performance is limited by the temporal and spatial coherence of the laser, we can take advantage of this and make IPDH with laminar illumination a means of obtaining these laser properties. The proposed method could be of interest for the optics community since it could be used for any type of light source, presenting some advantages by comparing it with other well-established techniques. It has been tested by using a high repetition rate laser commonly used in velocimetry and the results have been compared to those obtained with other standard techniques, verifying the well-functioning of the IPDH-based technique.