Measuring the gain dynamics in a conjugated polymer film
  We present a simple method for measuring the gain decay time in a conjugated polymer film by optically exciting the film with two mutually delayed ultrashort pump pulses. When the pump is set at such a power level that amplified spontaneous emission marginally develops along the polymer waveguide, the total output emitted from its edge decays exponentially as a function of the interpulse delay. The corresponding decay time represents the decay time of the gain of the polymer material. 
S.A. van den Berg, V.A. Sautenkov, G.W. 't Hooft, E.R. Eliel