Remote metrology by comparative digital holography

Abstract

A method for the remote comparison of objects with regard to their shape or response to a load is presented. The method allows interferometric sensitivity for comparing objects with different microstructure. In contrast to the well-known incoherent techniques based on inverse fringe projection this new approach uses the coherent optical wave field of the master object as a mask for the illumination of the sample object. The coherent mask is created by digital holography to allow instant access to the complete optical information of the master object at any place desired. The mask is reconstructed by a spatial light modulator (SLM). The optical reconstruction of digital holograms with SLM technology allows modification of reconstructed wavefronts with respect to improvement of image quality, the skilled introduction of additional information about the object (augmented reality), and the alignment of the master and test object.

Quantization noise and its reduction in lensless Fourier digital holography

“…This information can be analyzed with numerous digital processing methods. The advantage of numerical processing has helped digital holography become a fast growing field with numerous applications including aberration-compensated phase-contrast microscopy [5,6], shape measurement [7], and 3D display [8]. Recently, the resolution of CCD/CMOS sensors has increased significantly and with it, so, too, has the computational requirement of a digital holographic imaging system.…”

Speed up of Fresnel transforms for digital holography using pre-computed chirp and GPU processing

“…Since the reconstruction is done by propagating light numerically any known systematic aberrations in the optical setup can also be numerically compensated. Another advantage of digital holography is that the holograms can be transmitted to another place to be reconstructed remotely and studied 10,11 . The resolution of the reconstructed object primarily depends on the sensor area size, the total number of pixels in the camera and the bitdepth of the camera 12 .…”

Single Shot Dual-Wavelength Digital Holography: Calibration Based on Speckle Displacements

“…[17][18][19] Different laser sources in the single shot measurements, induce extra aberration and pseudo phase changes that can be suppressed by applying the modified flat fielding method. [9,11,20] In the flat fielding method they use a single dark frame and a flat frame captured from the system containing dual wavelengths to calibrate the measured data. One possible problem with the flat fielding method is an increase of the noise level because of division with intensity values close to zero.…”