Intensity fluctuations in forward scattering and temporal coherence.
The problem of forward scattering by a nonergodic system of identical particles is considered. The analysis of statistical characteristics of intensity fluctuations arising as a result of finite observation time shows that the mean dispersion of intensity fluctuations can be expressed as a function of the wavelength, diffusion coefficient, scattering angle, and observation time. The relation between the temporal correlation function of the scattered radiation and its second-order intensity moments is established. Quantitative estimates of the effect with the infrared laser beam propagating through fog give results comparable to the dispersion due to refractive index fluctuations in a pure atmosphere (Tatarskii).
Coherence-loss of laser light propagated through simulated coastal waters
Research is currently underway to investigate the physical mechanisms which cause loss of coherence in scattered light. It has been shown that, for Brownian motion of particles in a scattering medium, the coherence of incident light decreases rapidly with path length and diffusion coefficient. Experiments confirm that laser light scattered by a water column loses coherence as a function of path length and water turbidity. An experiment has been performed which measures coherence length versus temperature, optical path length, and water quality. The results are reported here. Based on these results and research into the causes of spectral broadening, experiments are proposed to measure each type of broadening mechanism with a much higher degree of accuracy.
rPET detectors design and data processing
Small animal PET systems based on rotating planar detectors posses some interesting advantages for high sensitivity, high resolution imaging. We have designed the rPET detectors based on MLS crystals assembled on a 30times30 matrix optically coupled to a flat-panel PS-PMT. Weighted position readout circuits pre-process the 64 signals from the 8times8 anodes matrix, which are digitized using a charge-integrating converter. The amplification electronics, including the trigger output for coincidence detection, and the high voltage supply are integrated in a three PCBs stack that forms the base attached to the back of the PMT. The whole assembly is enclosed in a light tight, lead (Pb) shielded aluminum box. The detectors are mounted on a rotating gantry with more than 180 degrees rotation span. The digitized events are screened and histogramed, and a modified center of gravity algorithm removes from the position calculation those signals with poor signal to noise ratio. Apparent mean crystal size on the 511 keV field-flood images is 0.6 mm, mean peak-to-valley ratio is better than 8, and intrinsic resolution is 1.5 mm at the central row, with the energy window wide open. Sensitivity (CPS) for a pair of these detectors set in coincidence at 160 mm distance is 1%