Random lasers are a type of lasers that lack typical resonator structures, offering benefits such as easy integration, low cost, and low spatial coherence. These features make them popular for speckle-free imaging and random number generation. However, due to their high threshold and phase instability, the production of picosecond random lasers has still been a challenge. In this work, we have developed three dyes incorporating polymer optical fibers doped with various scattering nanoparticles to produce short-pulsed random fiber lasers. Notably, stable picosecond random laser emission lasting 600 ps is observed at a low pump energy of 50 µJ, indicating the gain-switching mechanism. Population inversion and gain undergo an abrupt surge as the intensity of the continuously pumped light nears the threshold level. When the intensity of the continuously pumped light reaches a specific value, the number of inversion populations in the “scattering cavity” surpasses the threshold rapidly. Simulation results based on a model that considers power-dependent gain saturation confirmed the above phenomenon. This research helps expand the understanding of the dynamics behind random medium-stimulated emission in random lasers and opens up possibilities for mode locking in these systems.

研究了向列相液晶激光器件侧面激光辐射谱，并深入分析了激光辐射机制。分别制备了传统液晶盒和引入SU-8光栅结构的两种器件，并注入向列相液晶TEB30A和激光染料PM597的混合物。利用Nd：YAG固体脉冲激光器倍频出的532 nm激光作为泵浦源正面入射器件，侧面探测激光辐射谱。在传统液晶盒器件侧面，测得 575~600 nm范围的随机激光辐射谱。而具有周期100 μm和8 μm 的SU-8光栅结构器件侧面，获得了多波长激光辐射谱。随着泵浦能量增大，最高强度激光辐射峰波长位置出现在583~585 nm和588~592 nm附近，FWHM约0.3 nm。基于光波导理论结合器件结构分析得出，在传统液晶盒中引入SU-8光栅结构增强了液晶器件的光波导效应，是获得多波长激光辐射谱的主要原因。

The random fiber laser (RFL) has been an excellent platform for exploring novel optical dynamics and developing new functional optoelectronic devices. However, it is challenging for RFLs to regulate their emission into regular narrow pulses due to their intrinsic randomness. Here, through engineering the laser configuration (cavity Q value, gain distribution and nonlinearity), we demonstrate that narrow (~2.5 ns) pulses with record peak power as high as 64.3 kW are achieved from a self-Q-switched random ytterbium fiber laser. Based on high intracavity intensity and efficient interplay of multiple nonlinear processes (stimulated Brillouin scattering, stimulated Raman scattering and four-wave mixing), an over-one-octave visible-near-infrared (NIR) Raman-frequency comb is generated from single-mode silica fibers for the first time. After spectrally filtering the Raman peaks, wavelength-tunable pulses with durations of several hundreds of picoseconds are obtained. Such a high-peak-power random Q-switched fiber laser and wide frequency comb in the visible-NIR region can find applications in diverse areas, such as spectroscopy, biomedical imaging and quantum information.

提出一种基于光栅反馈技术的掺铥光纤随机激光器。激光器采用半开腔设计，封闭端采用中心波长为1 940 nm的高反射率光纤光栅为激光器系统提供强反馈，增益介质采用1.5 m长的掺铥光纤，泵浦源采用793 nm半导体激光器，开放端采用光纤随机光栅提供随机分布反馈。该光纤随机光栅由飞秒激光逐点刻写技术制备，在10 cm单模光纤上刻写超过6 000个间距随机分布的折射率畸变点，以增强光纤的后向瑞利散射效应。实验测得中心波长为1 940 nm的随机激光输出，其泵浦阈值为2.33 W，在3.8 W泵浦功率下的输出功率为57 mW，光信噪比达56 dB。输出激光在1 h内的波长偏移量小于0.1 nm，功率变化约0.26 dB，具有良好的稳定性。

采用溶剂热法分别制备了球形银纳米颗粒和多形貌银纳米颗粒, 其中球形银纳米颗粒具有400 nm的窄带等离激元共振峰, 而多形貌银纳米颗粒的共振区间在400~700 nm之间, 将它们分别掺入R6G与PVP的混合溶液中, 利用旋涂法在玻璃基板上制备银纳米颗粒嵌入染料掺杂聚合物薄膜随机激光器。 采用纳秒脉冲激光进行随机激光泵浦实验, 实验结果表明球形银纳米颗粒染料掺杂聚合物薄膜只有自发辐射峰, 而多形貌银纳米颗粒染料掺杂聚合物薄膜具有线宽<0.8 nm的相干随机激光发射光谱, 其阈值为1.9 mJ·cm^-2, 这可能是由于银纳米颗粒的等离激元共振区间与R6G的发射光谱重叠, 支持局域等离激元效应的形成, 明显的局域场增强有效地改善了与附近分子的相互作用, 从而激发了更多的辐射光子, 促进了高增益的形成。 进一步, 利用多形貌银纳米颗粒在银纳米颗粒染料掺杂聚合物薄膜中随机分布的特性, 通过改变泵浦位置, 实现了20 nm范围内的随机激光输出波长的调控, 具体输出范围为590.1~610.4 nm。 认为这是由于多形貌银纳米颗粒在不同位置的组成和分布不同, 改变了表面等离激元的相互作用和光子的散射能力, 从而形成不同的增益效应和不同的封闭光振荡路径。 此外, 考虑到多形貌银纳米颗粒的共振波长较宽, 探究了其用于输出其他颜色光的可能性。 以与上述银纳米颗粒R6G染料掺杂聚合物薄膜相似的制备方法, 制备了多形貌银纳米颗粒掺杂DCJTB染料聚合物薄膜, 并且进行随机激光泵浦实验。 结果表明, 可以有效的产生波长为675 nm, 半高宽<0.8 nm的相干红光随机激光, 并且阈值仅为0.98 mJ·cm^-2。 研究结果在宽带可调谐随机激光器研究以及多色随机激光器研究领域具有重要的参考价值。

将向列相液晶TEB30A、手性剂S-811、激光染料PM597的混合物填充空芯光子晶体光纤中，以Nd: YAG倍频532 nm激光作为泵浦光源，测量激光辐射谱，研究了光子晶体光纤载体中的随机激光辐射行为。泵浦激光侧面入射，侧面出射随机激光波长范围为590~605 nm，半高全宽约为0.3 nm；辐射方向较广。泵浦光端面入射，端面出射随机激光波长范围为580~605 nm，半高全宽约为0.3 nm。加热样品至各向同性温度时，端面和侧面激光辐射被关断。由实验结果得出，光子晶体中随机激光辐射源于微孔中填充的染料掺杂液晶混合物。手性向列相液晶中光子传输平均自由程和液晶分子介电张量的涨落随温度的变化，是影响出射激光强度的主要因素。