High-Particle-Density YAG:Ce Phosphor Coating for High Power Laser Lighting

Inorganic Ce doped yttrium aluminum garnet (YAG:Ce) fluorescent plates based on various manufacturing methods have been studied in recent years for laser lighting systems. A laser lighting optical system is designed to generate high central intensity beam, and light spreading effect for both YAG single crystal and YAG/Al2O3 composite is investigated. YAG single crystal and YAG/Al2O3 composite lose 50.8% and 25.9% of their light power from central pumping area, respectively, resulting in proportional decrease in central intensity. To solve this problem, a low-cost YAG:Ce high-particle-density phosphor coating (HPD-PC) was prepared for Etendue-limited applications. With only 8.5% of light spreading, under 47.7 W/mm2 pumping power density, YAG HPD-PC emits 1880 lm with the conversion efficiency of 157 lm/W. YAG HPD-PC also could work well under power density more than 100 W/mm2.

Assembly along lines in boundary-driven dynamical system

We introduce a simple dynamical rule in which each particle locates a particle that is farthest from it and moves towards it. Repeated application of this algorithm results in the formation of unusual dynamical patterns: during the process of assembly the system self-organizes into slices of low particle density separated by lines of increasingly high particle density along which most particles move. As the process proceeds, pairs of lines meet and merge with each other until a single line remains and particles move along it towards the zone of assembly. We show that this pattern is governed by particles (attractors) situated on the instantaneous outer boundary of the system and that both in two and in three dimensions the lines are formed by zigzag motion of a particle towards a pair of nearly equidistant attractors. This novel line-dominated assembly is very different from the local assembly in which particles that move towards their nearest neighbors produce point-like clusters that coalesce into new point-like clusters, etc.

Superfluidité excitonique dans Cu2O

The transit time of excitons through several millimeters of Cu2O is measured by the photovoltaic effect. A sudden reduction of velocity dispersion at high particle density and low temperature is attributed to superfluid excitonic motion.