Discrete-mode ZnO microparticle random laser

Abstract

A random laser incorporating irregular-shaped ZnO microparticles exhibits a small number of lasing lines with stable lasing intensities and negligibly low background emission. This unique feature is in direct contrast to that observed for a conventional ZnO nanoparticle film random laser. Gain competition between the discrete laser modes also occurs in this microparticle random laser. These lasing characteristics are because of the intra-particle confinement of the laser cavity modes in each ZnO microparticle.

Temperature dependence of lasing characteristics of irregular-shaped-microparticle ZnO laser

“…The irregular-shaped microparticle has a diameter of ∼2 µm. To examine the lasing properties of a single microparticle, a sample with a small number of scattered ZnO microparticles was prepared, similar to the procedure followed in our previous work [8]. The particles were dispersed in methanol, the resulting methanol solution was dropped onto a silicon substrate, and the substrate was rotated at 5000 rpm on a spin coater for 40 s. As a result, each ZnO microparticle exhibited clear separation (∼50 µm) from the other microparticles, as shown in Fig.…”

“…The particles were dispersed in methanol, the resulting methanol solution was dropped onto a silicon substrate, and the substrate was rotated at 5000 rpm on a spin coater for 40 s. As a result, each ZnO microparticle exhibited clear separation (∼50 µm) from the other microparticles, as shown in Fig. 4(a) of [8]. To measure the lasing characteristics of a single ZnO microparticle, we set the excitation laser spot size (∼14 µm) to be smaller than the microparticle separation.…”

“…Recently, we developed a new type of ZnO microlaser, i.e., an irregular-shaped-microparticle laser [8]. In this type of laser, the lasing oscillation arises from random multiple scatterings of light within the microparticle.…”

Double threshold behavior in a resonance-controlled ZnO random laser

“…So far, as gain materials, many studies on UV ZnO lasers have also been reported in various micro-/nano-cavity structures, such as random structures, [1][2][3][4][5][6][7][8][9][10][11][12][13] Fabry-Perot cavities, [14][15][16][17] whispering-gallery-mode resonators. [18][19][20][21] Although, in most of these ZnO lasers, the gain from electron-hole plasma (EHP) recombination under high excitation intensity condition has typically been reported as the origin of the stimulated emission (photon lasing), 12,13 the lasing originated by excitonic recombination, so-called polariton/exciton lasers, has also been demonstrated in well-designed cavity structures at room temperature.…”

“…In particular, because ZnO has the above-mentioned advantages and high gain, there are numerous studies on RLs so far. [1][2][3][4][5][6][7][8][9][10][11][12][13] In typical random structures, because localized modes are spontaneously formed and its modal control is difficult due to the multiple light scattering, the lasing peak wavelengths depend mainly on the property of gain materials and their thresholds are determined by the mean scattering property of the structure. Furthermore, the features of the RL (e.g., multimode lasing and high thresholds) make it difficult to realize strong interactions between cavity modes and gain materials and observe cavity-related phenomena, [21][22][23][24] like observed in well-designed resonators, as mentioned above.…”