Origins of lasing emission in a resonance-controlled ZnO random laser

Toshihiro Nakamura,Hideki Fujiwara,Keiji Sasaki,Naoto Koshizaki,Yoshie Ishikawa,Takeshi Tsuji,Sadao Adachi,Ryo Niyuki

doi:10.1088/1367-2630/16/9/093054

Abstract

We investigate the origins of lasing emission in a scatterer-resonance-controlled random laser made of ZnO nanopowder over a wide temperature range (20–300 K). At higher temperatures ( K), the lasing emission appears around exciton recombination energies and the lasing threshold carrier density is comparable to the Mott density, indicating that the resonance-controlled random laser is going toward showing excitonic lasing; at lower temperatures, random lasing is caused by usual electron–hole plasma recombination because of the threshold carrier density being much larger than the Mott density.

Highlights

Random lasers have a simple structure, consisting of randomly shaped nanopowder as a scatterer and luminescent material as an optical gain material
At T = 300 K (figure 1(d)) the randomly shaped ZnO powder shows a large number of spike-like peaks, that are attributed to random lasing arising from multiple scattering in the media
In the defect-site lasing system, the gain is achieved by light emission from ZnO powder surrounding the defect site, and the localized light field is not restricted in the defect site itself but properly penetrates into the ZnO powder area

Summary

Introduction

Random lasers have a simple structure, consisting of randomly shaped nanopowder as a scatterer and luminescent material (e.g., dye molecules [1], rare-earth ions [2] and semiconductors [3, 4]) as an optical gain material. To experimentally verify our proposed method, we prepared a random laser from homogenized spherical ZnO nanopowder and introduced polystyrene particles as defect sites We observed that this laser had features clearly distinct from those of normal ZnO random lasers; it exhibits quasi-single-mode lasing emissions with thresholds at room temperature much lower than those of normal ZnO random lasers [17]. In such resonance-controlled-type ZnO random lasers, the lasing characteristics are expected to depend on the gain properties of ZnO and the resonance properties of the resonant scatterer. We discussed the origins of the resonance-controlled lasing emission on the basis of the temperature dependence of the excited carrier densities at the lasing thresholds

The experiment

Results and discussion

Conclusion