ULTRAFAST STUDIES OF STIMULATED-EMISSION AND GAIN IN SOLID FILMS OF CONJUGATED POLYMERS

The recent discovery of gain narrowing in conjugated polymers has plac ed new emphasis on understanding the details of stimulated emission (S E) and gain in these plastic laser materials. In this Letter, the resu lts of ultrafast SE and photoinduced absorption (PA) measurements on f ilms of (2-butyl-5-(2'-ethyl-hexyl)-1,4-phenylenevinylene) (BuEH-PPV), a conjugated polymer that demonstrates gain narrowing above threshold , are presented. The approximate to 60 ps SE gain decay time of BuEH-P PV is significantly longer than that of most other conjugated polymers , allowing ample time for lasing to occur. We argue that the existence of gain is limited by a dynamic blue-shift of the PA resulting from i nterchain interactions.