Design of materials and cavities for organic lasers

Summary form only given. We will report on the spatial and energetic funneling of excitations in organic films through one or more resonance energy transfer (or Forster transfer) steps which is shown to be promising in the design of materials for use in very low threshold lasers. The main advantages of employing gain media with Forster transfer in organic thin film lasers stem from a combination of efficient absorption of the pump light, very low absorption at the emission wavelength and broad tunability. The lowest threshold powers for stimulated emission (amplified spontaneous emission) in unpatterned films are less than 100 W/cm². We also describe the characteristics of a variety of photopumped lasers with Forster gain media. The cavity designs we have employed include planar microdisks and oblate spheroids in which the lasing modes are whispering gallery modes, and distributed Bragg reflector based architectures. In many of these lasers, we have obtained true single mode operation, with resolution limited linewidths of 0.2 nm. The materials used for the acceptors (guests) include molecules, oligomers as well as conjugated polymers