Temperature dependence of the laser emission threshold in organic semiconductor lasers

Summary form only given. Despite numerous reports of line narrowing and laser emission in optically pumped conjugated polymers, the demonstration of electrically injected polymer lasers remains a challenging task due to the high pump power requirement for laser emission. The current studies focus on the development of low threshold laser geometries such as whispering gallery mode lasers, and on a better understanding of the mechanisms that are responsible for line narrowing and gain in conjugated polymers. Laser emission in conjugated polymers is generally described in terms of a four level system analogous to that used for laser dyes. In this model, excitation starts mainly from the lowest vibrational level of the ground state S/sub 0/ (/spl nu/=0) (level I) and populates higher vibrational levels of the excited state S/sub 1/ (/spl nu/´/spl ne/0) (level II). After relaxation, emission occurs from the lowest vibrational level of the excited state S/sub 1/ (/spl nu/´=0) (level III) to a higher vibrational level of the ground state S/sub 0/ (/spl nu//spl ne/0) (level IV). Previous studies have suggested that the threshold for line narrowing and laser emission was limited by the population of level IV at thermal equilibrium and that this threshold could be reduced significantly by lowering the temperature. We studied the temperature dependence of whispering gallery mode microring lasers using the conjugated polymer BEH:PPV as a gain medium.