Measurement of cavitation in a sliding bearing using digital holography

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Although most of the mathematical models for cavitation in bearings provide reasonable estimates of engineering parameters such as load capacity and friction, they are based on substantially different assumptions and further work is required to understand the fundamental operation of bearings. In this study digital holography was used to examine bubble formation within a glass sliding bearing. Digital holography collects the both the phase and amplitude of the transmitted wavefront and therefore contains quantitative information concerning the thickness of the cavitation bubbles. This paper introduces the experimental configuration and the digital holography system used to study cavitation. It also discusses the demodulation process and how the information can be used to find other interesting parameters such as bubble position and shape

Grid computing for the numerical reconstruction of digital holograms

Digital holography has the potential to greatly extend holography's applications and move it from the lab into the field: a single CCD or other solid-state sensor can capture any number of holograms while numerical reconstruction within a computer eliminates the need for chemical processing and readily allows further processing and visualisation of the holographic image. The steady increase in sensor pixel count and resolution leads to the possibilities of larger sample volumes and of higher spatial resolution sampling, enabling the practical use of digital off-axis holography. However this increase in pixel count also drives a corresponding expansion of the computational effort needed to numerically reconstruct such holograms to an extent where the reconstruction process for a single depth slice takes significantly longer than the capture process for each single hologram. Grid computing - a recent innovation in largescale distributed processing -provides a convenient means of harnessing significant computing resources in an ad-hoc fashion that might match the field deployment of a holographic instrument. In this paper we consider the computational needs of digital holography and discuss the deployment of numericals reconstruction software over an existing Grid testbed. The analysis of marine organisms is used as an exemplar for work flow and job execution of in-line digital holography

Shot Noise in Digital Holography

We discuss on noise in heterodyne holography in an off-axis configuration. We show that, for a weak signal, the noise is dominated by the shot noise on the reference beam. This noise corresponds to an equivalent noise on the signal beam of one photoelectron per pixel, for the whole sequence of images used to build the digital hologram

Stand-off 3D face imaging and vibrometry for biometric identification using digital holography

Lockheed Martin Coherent Technologies (LMCT) has demonstrated 3D face imaging at ~ 1-2 mm lateral resolution and range precision at stand-off distances up to 100 m using digital holography. LMCT has also demonstrated the digital holography technique in a multi-pixel vibrometry mode in the laboratory. In this paper, we report on 3D face imaging using multiple-source (MS) and multiple-wavelength (MW) digital holography breadboards. We will briefly discuss the theory of 3D imaging using MS and MW digital holography with references to the literature. We will also briefly discuss the theory of vibrometry using a digital holographic setup. We then describe our implementation of these techniques in breadboard setups operating at 1550 nm wavelength (for MS digital holography) and at wavelengths near 1617 nm (for MW digital holography). We also present experimental results for 3D imaging and for vibrometry with these digital holographic setups

Roadmap on digital holography [Invited]

This Roadmap article on digital holography provides an overview of a vast array of research activities in the field of digital holography. The paper consists of a series of 25 sections from the prominent experts in digital holography presenting various aspects of the field on sensing, 3D imaging and displays, virtual and augmented reality, microscopy, cell identification, tomography, label-free live cell imaging, and other applications. Each section represents the vision of its author to describe the significant progress, potential impact, important developments, and challenging issues in the field of digital holography

Digital Holography at Shot Noise Level

By a proper arrangement of a digital holography setup, that combines off-axis geometry with phase-shifting recording conditions, it is possible to reach the theoretical shot noise limit, in real-time experiments.We studied this limit, and we show that it corresponds to 1 photo-electron per pixel within the whole frame sequence that is used to reconstruct the holographic image. We also show that Monte Carlo noise synthesis onto holograms measured at high illumination levels enables accurate representation of the experimental holograms measured at very weak illumination levels. An experimental validation of these results is done

Feed particle size evaluation: conventional approach versus digital holography based image analysis

The aim of this study was to evaluate the application of image analysis approach based on digital holography in defining particle size in comparison with the sieve shaker method (sieving method) as reference method. For this purpose ground corn meal was analyzed by a sieve shaker Retsch VS 1000 and by image analysis approach based on digital holography. Particle size from digital holography were compared with results obtained by screen (sieving) analysis for each of size classes by a cumulative distribution plot. Comparison between particle size values obtained by sieving method and image analysis indicated that values were comparable in term of particle size information, introducing a potential application for digital holography and image analysis in feed industry