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

TLDR

The study is motivated by the challenge of achieving electrically pumped organic semiconductor lasers. The authors investigate optically pumped waveguide and microcavity lasers fabricated from vacuum‑deposited thin films of small‑molecular‑weight organic semiconductors. They create these lasers by vacuum deposition of thin organic semiconductor films to form waveguide and microcavity structures. The resulting lasers achieve high output powers (up to 50 W in waveguides and 3 W in microcavities), low thresholds (1 μJ/cm² and 300 μJ/cm²), lifetimes exceeding 10⁶ pulses, tunable wavelengths from 460 to 700 nm, temperature‑stable operation up to 140 °C, and ultra‑narrow linewidths of 0.2 Å limited by 40 ps relaxation oscillations, with theoretical linewidths at least an order of magnitude smaller than inorganic diodes.

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 (1 μJ/cm2), and long operational lifetime (>106 laser pulses at 100 times the threshold pump power). Microcavity laser characteristics include 3 W peak output power, 300 μJ/cm2 lasing threshold, and lifetimes of >106 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.