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Nastupno predavanje: Holography and coherent optics Hrvoje Skenderović
Institute of Physics
16/05/2023/ at 11:00h
Institute of Physics, 1st Wing, Lecture room

The topic of the talk is research in the field of Digital Holography and connected themes. Especially, implementation of holographic measurements with scanning single photon avalanche detector (SPAD), as well as time-averaged digital holography (TADH) is presented. In TADH measurements, holograms of a vibrating object are recorded, usually in such a way that the exposure period of the camera recording the hologram is many times greater than the period of vibrations. We examined the error in the reconstruction if the exposure time is only a few times greater than the oscillation period and if it is a non-integer ratio of the two times. In the following, we have shown that it is possible to obtain an accurate hologram even when the exposure is only half the oscillation period with a known phase. Finally, we have given a procedure for determining the unknown oscillation period and phase with several short exposures. All these numerical calculations were confirmed by experimental measurements with real objects. 

We also investigated the differences in sampling and nonlinearities in holography using a SPAD detector and a camera. We have shown how it is possible to determine the optimal sampling using a scanning detector. Also, the standard camera mainly works with an 8-bit image, that is, it has 256 gray levels, which easily leads to saturation in the recording, or to the appearance of non-linear members in the reconstruction of the hologram. In contrast, SPAD as a detector has an infinite dynamic range.

An experiment dealing with application of quantum light in holography is also discussed. The objective is to use individual photons in a classic holographic setup and see if they can be used to obtain a hologram and if visibility improves compared to classic source of the same (very low) intensity. Since holography is based on the interference of two light beams, and in the case of individual photons we a photon can not be split at the BS, the possibility of interference is not clear a priori. Also, there is a problem with the phase, which is indeterminate for individual photons. It is shown that a hologram can be recorded, amplitude and phase reconstruction can be obtained, and the SNR is better compared to classical light of the same intensity.

Predsjednik Znanstvenog vijeća Instituta za fiziku
dr. sc. Damir Starešinić
IF Ⓒ 2017