- Zinc oxide -- Electric properties,
- Zinc oxide thin films,
- Optoelectronic devices -- Materials -- Mathematical models,
- Photonics -- Mathematical models,
- Semiconductor lasers
Zinc oxide (ZnO) is a wide bandgap n-type semiconductor with a variety of optical and electrical applications and many methods of fabrication. Strong optical scattering and photoluminescence from ZnO nanoparticles and films makes the material an ideal candidate for a random laser. Previous studies have shown both incoherent and coherent random lasing from ZnO films and particles agglomerations. When used as a passive scatterer in a laser dye gain medium, the addition of ZnO has been shown to improve the threshold for lasing. By combining active scattering ZnO with a passive scatterer, MgO, we show here that the lasing threshold is reduced. We also demonstrate strong optical feedback in laser pumped ZnO nanoparticle films. Photoluminescence (PL) results show a clear amplification threshold and the resulting non-linear behavior. We find that shortening the pump pulse time by a factor 6 causes a feedback mechanism transition from Amplified Spontaneous Emission (ASE) to Non-resonant feedback (NRF). The pulse time is still longer than the excitonic lifetime (~200 ps), however the randomness from spontaneous emission is greatly reduced. NRF in our samples can be characterized by a dramatic narrowing of the photoluminescence peak around 387 nm to FWHM of ~3 nm, as well as a high degree of reproducibility in the emitted spectra. A new statistical model for the generation of random laser modes was formulated and it reproduces the experimental results. Further work will focus on studying the transition from non-resonant to resonant feedback in the nanoparticle films.
Available at: http://works.bepress.com/rolf_koenenkamp/1/