Double-sideband filter for digital holography

C. RAMIREZ; A. LIZANA; C. IEMMI; J. CAMPOS

San Francisco

Congreso; Photonic Instrumentation Engineering IV; 2017

Nowadays, digital holographic systems are based on two main optical schemes: off-axis (OA) and inline (IL)holographic systems. In OA set-ups, the reference and the object beams present a relative angle at the registration plane.Thus, a real image of the object can be obtained without the influence of conjugated images by performing a spatialfiltering at the reconstructed plane. IL configurations are less sensitive to vibrations and air flows than OAconfigurations, but the undesired influence of conjugated images in the final hologram is not avoided. To overcome thislimitation, a number of IL based methods have been proposed. One interesting approach is the phase-shifting technique,which leads to efficient holograms for IL applications. However, due to the time-sequential nature of this technique, it issomewhat inappropriate for dynamic processes. We present a new method, for IL digital holography, based on a doublesideband(DSB) filter. This method not only removes the conjugate images in the reconstruction process but also reducesthe distortions that usually appear when using single-sideband filters. Moreover, it is only time-limited by the acquisitiontime of the CCD camera. The appropriateness of the technique to be applied in dynamic processes was tested for thetracking of micro-particles. To this aim, particle holographic images were obtained by using the DSB method andafterwards processed with digital picture recognition methods, this allowing us to accurately track the spatial position ofthe particles. By using this approach, the instantaneous trajectory and velocity described by glass microspheres inmovement were experimentally determined