We present results from a pitcher-catcher experiment utilizing a proton beam generated with nanostructured targets at a petawatt-class, short-pulse laser facility to induce proton-boron fusion reactions in a secondary target. A 45-fs laser pulse with either 400 nm wavelength and 7 J energy, or 800 nm and 14 J, and an intensity of up to 5 × 10²¹ W/cm² was used to irradiate either thin foil targets or near-solid density, nanostructured targets made of boron nitride (BN) nanotubes. In particular, for 800 nm wavelength irradiation, a BN nanotube target created a proton beam with about five times higher maximum energy and about ten times more protons than a foil target. This proton beam was used to irradiate a thick plate made of boron nitride placed in close proximity to trigger ¹¹B (p, α) 2α fusion reactions. A suite of diagnostics consisting of Thomson parabola ion spectrometers, postshot nuclear activation measurements, neutron time-of-flight detectors, and differentially filtered solid-state nuclear track detectors were used to measure both the primary proton spectrum and the fusion products. From the primary proton spectrum, we calculated (p, n) and (α,n) reactions in the catcher and compare with our measurements. The nuclear activation results agree quantitatively and neutron signals agree qualitatively with the calculations, giving confidence that primary particle distributions can be obtained from such measurements. These results provide new insights for measuring the ion distributions inside of proton-boron fusion targets.

飞秒激光在工业加工、精密测量、****、科学研究等领域具有广阔的应用前景。报道了基于光谱控制与色散优化的高功率、高脉冲质量飞秒啁啾脉冲放大系统。利用与压缩器色散量相匹配的色散可调啁啾布拉格光纤光栅(CFBG)作为展宽器,通过微调CFBG色散量补偿系统的残余色散使整个系统的净色散趋于零;同时引入光谱滤波等手段,保证入射到主放大器之前的脉冲光谱形状不发生畸变,避免了放大过程中脉冲质量的劣化。最终获得了重复频率为50 MHz、平均功率为24 W、脉冲宽度为198 fs的高脉冲质量飞秒激光输出。

针对高功率光纤飞秒激光放大器,介绍了啁啾脉冲放大(CPA)技术的基本原理,讨论了该结构中关键的展宽器和压缩器的发展现状与瓶颈;介绍了典型的大模场面积光纤的结构和工作原理,简介了基于大模场面积光纤的CPA系统的发展现状;介绍了非线性放大技术,讨论了实现更窄脉冲宽度、更高脉冲质量的光纤飞秒激光放大方案;最后分析了全光纤结构、相干合束、单晶光纤增益介质以及皮秒种子源等新型技术,并总结了高功率光纤飞秒激光放大器的发展趋势。

采用数值模拟的方法, 研究了周期性光谱调制对飞秒脉冲自相似放大的影响。构建了叠加光谱调制的飞秒脉冲自相似放大的理论模型, 分析任意相移量、调制深度和调制周期等参量变化对自相似放大系统的影响。结果表明, 任意相移量虽然会改变被调制后光谱具体形状, 但不会影响自相似放大的时域结果; 调制周期较大时, 子脉冲和主脉冲重叠, 对自相似放大过程和结果造成一定程度的破坏; 调制周期较小时, 主脉冲独立放大, 基本不会被子脉冲影响, 这一结论在调制深度改变时依然成立。

采用光纤啁啾脉冲放大技术,搭建了基于负三阶色散补偿的高功率、高脉冲质量全光纤飞秒激光放大系统。利用保偏大模场双包层掺镱光纤作为增益介质,负三阶色散光纤和普通保偏单模光纤作为混合型光纤展宽器,在实现时域展宽的同时,对放大系统中的正三阶色散进行预补偿,从而获得高质量、高功率的激光脉冲输出。在实验中使用混合展宽器和1200 line·mm ^-1光栅对作为压缩器,使系统的净三阶色散量趋近于零,最终获得了重复频率为111 MHz,放大后输出平均功率为8.5 W,中心波长为1035 nm,去啁啾后脉冲宽度为217 fs的高脉冲质量飞秒激光输出。

Usually, only focused femtosecond (fs) lasers at near-infrared (NIR) range can induce photo-damage to transparent cells, making it difficult to treat large amount of cells by such optical methods for photostimulation. In this study, we clarify the mechanism of photodamage to cells that are co-cultured with gold nanorods (GNRs) by fs laser. The pulse duration and repetition rate of the fs laser play a key role in cell damage suggesting that the heat accumulation con-tributes to the major part for the cell damage rather than the high peak power which mainly determines the efficiency of multiphoton excitation. We further show that cellular Ca2t can also be released in this scheme, but the process is more sensitive to peak power. Our results can provide a large-scale GNR-mediated photostimulation for cell signaling modulation.

利用普通大模场面积掺镱保偏双包层光纤作为增益介质，采用啁啾脉冲放大技术搭建了全保偏光纤飞秒激光放大系统。由于全保偏光纤结构，系统具有较高的集成度和长期稳定性。将系统中积累的三阶色散与放大过程中引入的非线性啁啾相互补偿，通过控制展宽光纤的长度，优化了压缩后脉冲质量和宽度。同时分析了周期性光谱调制对放大输出的影响，通过优化保偏（2+1）×1光纤合束器的制作工艺，解决了其引起的周期性光谱调制问题，最终获得重复频率为111 MHz，压缩后输出平均功率为9 W，对应脉宽为260 fs，单脉冲能量为81 nJ，保偏比为13 dB的高质量飞秒激光脉冲输出。