基于金属纳米结构而获得随机激光的增强, 其独特的性质及其潜在的应用价值具有重要的研究意义, 在表面增强荧光、 光学开关器件、 表面等离子激元激光等方面实现了较多应用。 报道一种快捷有效的制备纳米颗粒的手段并基于该纳米颗粒结构分析了染料掺杂聚合物薄膜涂覆的随机激光现象和规律。 利用离子溅射沉积和高温热处理在石英基底上制备了Au纳米颗粒, 改变溅射时间Au纳米颗粒的尺寸发生可控变化, 该方法便捷、 工艺简单。 研究采用40, 80和120 s三种不同的时间进行Au膜溅射并在650 ℃下高温处理, 得到粒径尺寸不同的Au纳米颗粒, 随着溅射时间延长Au纳米颗粒的尺寸逐渐变大。 通过涂覆有机荧光染料DCJTB掺杂的PMMA聚合物薄膜构建光致激射系统, 利用纳秒脉冲激光对样品进行激发, 得到随机激光并研究其出射光强度和阈值的变化规律特征。 40, 80和120 s三种溅射时间下所得Au纳米颗粒的平均粒径尺寸分别为230, 250和390 nm, 在532 nm激光激发下产生随机激光的阈值分别为20.5, 17.5和12.5 μJ·pulse-1。 Au纳米颗粒尺寸越大、 粒子间距越小时, 光子散射的平均自由程越短, 光在金属颗粒之间可以多次有效散射, 从而显著提高散射效率, 产生较低阈值的激光发射; Au纳米颗粒的吸收峰与染料的荧光峰恰好匹配时, 将会显著增强染料的荧光效应, 激发更多染料分子发生能级跃迁, 增加光子态密度, 获得峰值更高、 阈值更低的激射现象; 泵浦光不破坏染料分子的情况下, 可以多次循环泵浦获得激光, 染料分子的发光效率随着多次激发略有降低, 有助于随机激光器件的研究开发。 实验研究结果与理论分析相一致, 进一步明确了Au纳米颗粒对光子散射和等离子共振对光吸收增强的随机激光发射机理。 该研究以Au纳米结构对光子的强散射效应为增益, 通过理论分析和实验测量获得随机激光, 为实现高效率、 低阈值的随机激光研究提供了一种便捷的技术手段, 有望促进随机激光器件的开发和应用。

It’s of great significance toconduct researches of plasmonic enhanced random lasing based on metal nanoparticles which have special property and potential applications. Plasmonic enhanced random lasing has been used in surface fluorescence enhancement, optical switching device, surface plasmon laser and so on. In this paper, we propose a convenient and high-efficiency way to fabricate Au nanoparticles and study the random lasing property based on a dye-doped film covering on these particles. By changing sputtering time with 40, 80, and 120 s, different sizegold nanoparticles are prepared by sputtering and the rmal annealing on quartz substrate. The particle size increases with sputtering time enlarging. After being covered by DCJTB-doped PMMA film, low-threshold random lasing phenomenon is obtained by a 532 nm pulse beam pumping. In this study, themean particle size of Au nanoparticles, obtained at 40, 80 and 120 s sputtering time, is 230, 250 and 390 nm, respectively, and the threshold for generating random lasing under 532nm pump beam excitation is 20.5, 17.5 and 12.5 μJ·pulse-1, respectively. The larger the size and the smaller the particle spacing of Au nanoparticles, the shorter average free path of photon scattering. In that case, the light can be effectively scattered among metal particles for many times, so the scattering efficiency can be significantly improved, resulting in low threshold laser emission. When the absorption peak of Au nanoparticles is exactly matched with fluorescence peak of the dye, the fluorescence effect can be significantly enhanced. As a result, more dye molecules can be excited to generate energy level transition, and the density of photonic state is increased. During limit of damaging dye molecules by pump light, the laser can be obtained by stimulating dye molecules in multiple cycles with a slightly decrease of lasing intensity at the same level pump beam power, which is helpful for the research and development of random laser devices. The experimental results meet well with lasing theoretical analysis, which plays a significant role in clarifying random lasing emission mechanism of Au nanoparticles on photon scattering and plasmon resonance on optical absorption enhancement. Our study could provide a convenient technical method for high-efficiency and low-threshold random laser research which is expected to promote the development and application of random laser devices.