Three-dimensional surface measurement using digital holography with pulsed lasers

For medical application in the field of maxillofacial surgery, a highly resolved 3D digital representation of the human face is needed. Especially moving objects, i.e. infant patients are hard to capture with conventional systems. We eliminated moveable artifacts systematically by using eye safe holographic recording with short pulsed lasers (Nd:YLF laser, 526.5 nm wavelength). With a single pulse (35 ns, 1,4 J energy), surface data are recorded. Our conventional system uses an analogue process, where the hologram is reconstructed optically and digitized slice-by-slice. We explored the possibility for a complete digital process. The conventional analogue recording material is replaced by a CCD-sensor with significantly lower pulse energy (0.1 mJ) for exposure. Numerical reconstruction of the real image is performed on a computer using appropriate algorithms. Surface calculations can follow immediately. Using this digital holographic approach to measure 3D surfaces means, that processing time, costs and effort can be reduced. However, in terms of resolution, digital technology lags behind the capabilities of our current analogue method for 3D surface detection. This involves inherent limitations at the current technological state of sensor technology. Nevertheless first applications are already possible.