Start Date

7-5-2014 11:00 AM

End Date

7-5-2014 1:00 PM

Subjects

Zinc oxide -- Electric properties, Zinc oxide thin films, Optoelectronic devices -- Materials -- Mathematical models, Lasers, Photonics -- Mathematical models, Semiconductor lasers

Description

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.

Persistent Identifier

http://archives.pdx.edu/ds/psu/11425

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May 7th, 11:00 AM May 7th, 1:00 PM

Zinc Oxide Random Laser Threshold Enhancement via Addition of Passive Scatterers

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.