Figure 8.

(a) Optical gain measurements using a variable stripe-length (VSL) technique. In this method, a nanocrystal film is excited with a laser beam focused with a cylindrical lens into a narrow stripe, aligned perpendicular to the sample edge. The edge emitted light intensity is measured as a function of stripe length varied with a razor blade translated in or out of the laser beam. (b) An example of VSL measurements, which exhibit the emergence of a narrow ASE feature at sufficiently large stripe lengths (l). (c) The measured edge-emitted emission intensity (I_PL; circles) is fitted to I_PL = Al + Be^Gl (line), where G is the gain coefficient, and A and B are l-independent constants.