Thermal and optical investigations of a laser-driven phosphor converter coated on a heat pipe

Heat accumulation on phosphor converter is one of the most serious bottlenecks that impede the development of the laser illumination. In this work, a copper powder sintered flattened heat pipe coated with high reflectivity silver was utilized to dissipate the heat from the phosphor stimulated by three high power blue lasers (450 nm). In comparison, a conventional aluminum heat pipe with the same size of the heat pipe substrate was investigated either. The thermal and optical performances were experimentally evaluated. It was found that the heat pipe can lower the phosphor temperature and maintain the output radiant power constantly. Moreover, the heat pipe substrate can reduce the chromatic shift during the temperature rising. The correlated color temperature (CCT) deviation is only 292 K during a 1200 s measurement at an input current of 2.5 A. The highest driven power that the heat pipe substrate can sustain is 34.4 W, which is 14.7% higher than the aluminum substrate. In addition, the carbonization failure process of the phosphor and silicone mixture were revealed in this work. Some further research suggestions were also proposed on improving the thermal and optical performances of the laser illumination.