Tele-Metrology Based on Digital Holography

Television holography (TVH) can be defined as 'the family of optical measurement techniques based on the electronic recording and processing of holograms'. Image-plane TVH was introduced in the early 1970s with the name 'electronic speckle-pattern interferometry' (ESPI). Since then, TVH has undergone an impressive development and become one of the most promising optical techniques for non-destructive testing and industrial inspection. The aim of this review is to propose an original scheme for the systematic treatment of TVH and to review the existing techniques according to it. In this approach we split the measurement process into four highly independent stages (illumination and observation geometry, temporal treatment, secondary-correlogram generation and fringe-pattern analysis) and establish a common notation to formulate the corresponding techniques. Such a strategy allows the free combination of the techniques proposed for each stage as building blocks to obtain every particular variant of the whole TVH measurement process, whether it has already been reported or not, and also the incorporation of new techniques while retaining compatibility with the existing variants of the previous and following stages.

Section: Discussionmentioning

confidence: 99%

A systematic approach to TV holography

Doval

1999

“…To use equation (10) given the individual digital reconstructed intensities from the individual digital in-line holograms, it is necessary to have the mapping functions given by equation (8). These functions have to be determined using a calibration procedure which is described in the following section.…”

Section: Multi-camera (Tomographic) Digital Hologram Recording and Re...mentioning

confidence: 99%

“…The reconstructed individual midplanes are for each direction as shown in figure 16(a). The volume intensity iso-surface based on the reconstruction of 10 planes from each direction is shown in figure 16(b), which clearly shows the depth-of-field problem.In order to more distinctly show the reconstruction of one glass sphere and how the application of equation(10) to the three digitally reconstructed intensity fields result in the faithful reconstruction of the glass sphere a small subzone is shown in figure16(c)-note that the reconstructions of multiple planes for each recording direction is shown here and that the respective intensity fields have not been multiplied to extract the faithful glass sphere reconstruction. It can easily be recognized by reference to the second case depicted in figure6that the multiplication of these three intensity fields would result in the elimination of the depth-of-field problem and a reconstruction that closely approximates the shape of the spherical glass sphere.…”

mentioning

confidence: 99%

Towards 3C-3D digital holographic fluid velocity vector field measurement—tomographic digital holographic PIV (Tomo-HPIV)

Soria

Atkinson

2008

Most unsteady and/or turbulent flows of geophysical and engineering interest have a highly three-dimensional (3D) complex topology and their experimental investigation is in pressing need of quantitative velocity measurement methods that are robust and can provide instantaneous 3C-3D velocity field data over a significant volumetric domain of the flow. This paper introduces and demonstrates a new method that uses multiple digital CCD array cameras to record in-line digital holograms of the same volume of seed particles from multiple orientations. This technique uses the same basic equipment as Tomo-PIV minus the camera lenses, it overcomes the depth-of-field problem of digital in-line holography and does not require the complex optical calibration of Tomo-PIV. The digital sensors can be oriented in an optimal manner to overcome the depth-of-field limitation of in-line holograms recorded using digital CCD or CMOS array cameras, resulting in a 3D reconstruction of the seed particles within the volume of interest, which can subsequently be analysed using 3D cross-correlation PIV analysis to yield a 3C-3D velocity field. A demonstration experiment of Tomo-HPIV using uniform translation with nominally 11 µm diameter seed particles shows that the 3D displacement derived from 3D cross-correlation Tomo-HPIV analysis can be measured within 5% of the imposed uniform translation, where the imposed uniform translation has an estimated standard uncertainty of 4.3%. So this paper proposes a multi-camera digital holographic imaging 3C-3D PIV method, which is identified as tomographic digital holographic PIV or Tomo-HPIV.

“…Due to the small angles between the hologram normal and the rays from the hologram to the image points, the obliquity factor cos can normally be set cos = 1. Different approaches for the solution of (1) have been proposed [10]. The Fresnel approximation replaces the factor ρ by the distance d in the denominator of equation ( 2) and the square root in the argument of the exponential function is replaced by the first terms of a binomial expansion.…”

Section: Principle Of Digital Holographymentioning

confidence: 99%

Digital holography as a versatile optical diagnostic method for microgravity experiments

Kebbel

Adams

Hartmann

et al. 1999

Microgravity experiments require robust, reliable and simple measurement techniques that provide the same capabilities as on-ground laboratory applications. Interferometric measurement techniques such as conventional holographic interferometry using hologram plates have several disadvantages in microgravity research - a time-consuming development process and additional experimental effort for a quantitative evaluation of interference patterns, for example. Digital holography is an advanced optical diagnostic tool for surface deformation analysis, measurement of refractive index variations and particle analysis in transparent media: Fresnel holograms are stored electronically and the reconstruction is performed by numerical methods. Due to the reconstruction process a numerical representation of the recorded wavefront can be evaluated including amplitude and phase. This paper reports on applications of digital holography to particle analysis and to the detection of refractive index variations within transparent media. The properties and advantages of this technique for microgravity experiments with respect to other techniques are discussed.