ÜV2 - From Analog to Digital Holography – What is the Benefit?

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
SENSOR+TEST Conferences 2011
Proceedings SENSOR 2011
W. Osten - Universität Stuttgart (Germany)
19 - 19


There are several three-dimensional (3D) imaging methods based on interferometry that allow the measurement of minute displacements and surface profiles. Methods like holographic interferometry and speckle metrology can provide full-field noncontact information about coordinates, deformations, strains, stresses and vibrations. The basic principle of these methods consists in the transformation of phase changes into recordable intensity changes. Because of the high spatial frequency of these intensity fluctuations the registration of a hologram requires a light sensitive medium with adequate spatial resolution. Therefore special photographic emulsions have dominated holographic technologies for a long period. However, the recording of holograms on electronic sensors and their numerical reconstruction is almost as old as holography itself. First ideas and implementations came up already in the 60th and 70th. But only in the 90th the progress in high resolution camera technology and computer hardware opened a re l chance to record holograms directly on the CCD target of a camera and to reconstruct the wave front in a reasonable time. But digital holography is much more than an elegant recording technique. In contrast to conventional approaches digital holography allows the direct calculation of both parts of the complex wave front, phase and intensity, by the numerical solution of the diffraction problem in the computer. Several advantages for the measurement process result from that new quality. Besides the electronic processing and the direct access to the phase some further benefits recommend digital holography for the solution of numerous imaging, inspection and measurement problems. Some obvious advantages are: certain aberrations can be avoided and remaining aberrations can be corrected numerically, different object states can be stored independently, the number of necessary holograms for quantitative evaluations can be decreased considerably, and the size of holographic sensors can be reduced drastically. On e xample of practical applications these and some more advantages are discussed. However, the price that has to be paid for it is also taken into consideration.