Ultrafast studies of stimulated emission and gain in solid films of conjugated polymers

The recent discovery of gain narrowing in conjugated polymers has placed new emphasis on understanding the details of stimulated emission (SE) and gain in these plastic laser materials. In this Letter, the results of ultrafast SE and photoinduced absorption (PA) measurements on films of poly(2-butyl-5-(2′-ethyl-hexyl)-1,4-phenylenevinylene) (BuEH-PPV), a conjugated polymer that demonstrates gain narrowing above threshold, are presented. The ≈ 60 ps SE gain decay time of BuEH-PPV 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 interchain interactions.