Study of lasing action based on Förster energy transfer in optically pumped organic semiconductor thin films

Abstract

We present a study of optically pumped waveguide and microcavity lasers based on vacuum-deposited thin films of small molecular weight organic semiconductors. Lasing action in waveguide lasers is characterized by high output peak power (50 W), high differential quantum efficiency (70%), low lasing threshold $\text{(1\hspace{0.5em}}{\mathrm{\mu J/cm}}^{\mathrm{2}})$ , and long operational lifetime ${\text{(>10}}^6$ laser pulses at 100 times the threshold pump power). Microcavity laser characteristics include 3 W peak output power, $\text{300\hspace{0.5em}}{\mathrm{\mu J/cm}}^{\mathrm{2}}$ lasing threshold, and lifetimes of ${\text{>10}}^6$ pump laser pulses (operating at 6 times the threshold power). We demonstrate wavelength variability from 460 to 700 nm by changing the composition of the organic films. The confinement of excitations on the dopant molecules leads to quantum dot-like behavior such as high temperature stability of the lasing threshold, output power, and emission wavelength in the temperature range from 0 to 140 °C. The linewidth of laser emission from microcavity structures is found to be 0.2±0.1 Å and is transform limited by 40 ps long relaxation oscillations. We present a theoretical estimate for the linewidth of organic semiconductor laser emission which is found to be at least an order of magnitude smaller than for inorganic laser diodes. The prospects for realizing electrically pumped organic semiconductor lasers are considered.