Investigation of phase conjugation for medical imaging

Sammanfattning: With the development of extremely precise spectral filters based on spectral hole burning and slow light effects, the idea of their implementation in an Ultrasound Optical Tomography (UOT) medical imaging technique arose. Simulations have shown that the resulting Contrast-to-Noise (CNR) ratio is fairly good at depths up to 5 cm but decreases dramatically when probing deeper in tissue. One of the possible enhancements of this technique is to include a phase conjugator after the filter to reverse and amplify ultrasound-tagged photons and send them back to the area of interest. This project tries to investigate the possibilities of using rare-earth-ion-doped crystals as potential phase-conjugating elements in the UOT and is specifically aimed at studying the properties of an optical phase conjugation process in these media. Experimental work was done on two crystals doped with Praseodymium and the phase-conjugated signal was studied as a function of different parameters with results discussed and presented in the respective section. In particular, efficient phase conjugation was observed in a 6-mm thick Pr:YSO crystal with reflectivity values reaching up to 124 \%. Further outlook and possible applications are given at the end of the thesis.