KEYWORDS: Image filtering, 3D image reconstruction, Holograms, Charge-coupled devices, Diffraction, Holography, Confocal microscopy, Digital holography, 3D image processing, 3D displays
In this study, it is newly attempted to combine digital holography method to get the holography fringe data using the CCD with the pulsed electro-holographic system for real-time display. Owing to the one-dimensional characteristic of the Bragg regime AOSLM that the fringe data propagating in parallel with the laser incident plane in the crystal cannot diffract the incident reference beam vertically by the momentum conservation, the diffraction of vertical direction from the AOSLM is impossible and the vertical parallax is not generated. Therefore the confocal lens system with a horizontal slit is introduced to obtain proper interference pattern. When the display of pulsed laser electro-holographic system is made by the fringe data of which bandwidth is reduced, the image clearness and quality is more improved than the recorded data without the confocal system with a horizontal slit since the fringe is formed to give mainly the horizontal parallax and the bandwidth of vertical direction is reduced so that the one line of object is projected onto only one line pixels of the CCD at same height.
One of the main problems in practical application of digital holography is that the unit cell size of CCD(Charge-Coupled Device) is too large. As a result, the object size of recording of interference pattern to CCD is very limited. The angle of incoming laser light ray is reduced by the ratio of two focal lengths of two confocal lenses. This induces the spatial frequency of interference pattern to be lower. So the higher spatial frequency of interference pattern than the spatial frequency determined by the unit cell size of CCD, can be recorded. By using confocal lenses optical setup, a merit can be achieved like that the area of the 0-th order diffraction light is reduced to the square of the ratio of two focal lengths at numerical reconstruction. As a result, numerical reconstruction for larger object size compared with CCD only case, is calculated by using FFT(Fast Fourier Transform) adapted to the integral came from Huygens-Fresnel principle. The needed diameters of two confocal lenses and the position of CCD camera are calculated for recoding the interference pattern of larger object size.
The application of pulsed laser in real time holography base don acousto-optic (AO) cells allows to get rid of mechanical horizontal scanning. The improvement of recently reported real time pulsed holographic display is presented. Ar-ion laser, used before as a coherent light source, is replaced with Q-switching Nd:YVO4 laser with SHG, operated by external triggering at 46 kHz. The commercial PC dual monitor graphic card was adapted to generate six parallel analogue outputs to feed six AO cells with gray scale hologram data. The upgrade improves brightness and clearness of reconstructed images and reduces the system dimensions and power consumption. 2D and 3D images reconstructed from precomputed HPO holograms are presented.
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