以晶面<100>的硅片为研究对象，使用重复频率1 kHz的超快复合双脉冲作为激发工具，通过研究双脉冲之间的偏振夹角、延迟时间和脉冲数对周期性结构面积的影响，探究引起周期性结构演化的非线性电离动力学。实验结果表明，在激光能量密度为0.23 J/cm²、脉冲组合为100个的复合脉冲辐照条件下，正交偏振诱导的结构面积最小，相比于其他入射形式下诱导的最大面积减小率约为45%，这是因为局域场的反复调制抑制了周期性结构边缘烧蚀阈值的降低。在正交偏振时，随着两束脉冲之间延迟时间的改变，通过观察诱导结构面积变化可以分析从电子电离到物质喷发的连续过程。该复合脉冲调控技术可为研究超快激光诱导半导体表面周期性结构的偏振依赖性与电子电离效率提供参考，进一步的改进有望实现超衍射极限结构的快速诱导。

熔盐堆作为第四代先进反应堆的重要堆型之一，以高沸点熔盐为核燃料熔融载体，具有高温输出、常压操作等特点。而基于温差发电的热管熔盐堆，兼具了熔盐堆、热管和温差发电的优势，具有输出温度高、热电转换效率高、结构简单及安全可靠等优点，在能源系统领域具有极大的优势，是外太空及深海探测任务的理想能源。但因堆芯熔盐低热导率而形成的热管密集排布给热管冷凝段的温差发电传热设计带来了难题。针对该堆型设计需求，本文提出适于熔盐堆的热管-温差发电耦合系统结构并进行了传热分析。堆芯热管冷凝段采用塔式温差发电系统结构设计，整体热端座与堆芯热管冷凝端相配合，形成从下至上的第1层至第N层热段套；冷端座套置于热端座外，内设冷端热管通道；热端座的外侧壁与冷端座的内侧壁之间贴有温差发电片，发电片间隙采用保温棉减少漏热。采用Ansys Workbench开展了适于热管熔盐堆的4层塔式温差发电系统传热仿真模拟，分析表明：系统运行的高温热管最高温度为696 ℃时，整体塔座温度分布均匀，热量有效利用率大于96%，系统漏热量小于4%，发电片两侧温差大于490 ℃，利于提高热电转换效率，设计具有可行性，有利于推动温差发电在热管熔盐堆中的应用。

We designed a femtosecond (fs) + picosecond (ps) double-pulse sequence by using a Mach–Zehnder-like apparatus to split a single 120 fs pulse into two sub-pulses, and one of them was stretched to a width of 2 ps by a four-pass grating system. Through observing the ripples induced on the ZnO surface, we found the ionization rate appeared to be higher for the sequence in which the fs pulse arrived first. The electron rate equation was used to calculate changes of electron density distribution for the sequences with different delay times. We suggest that using a temporally shaped fs+ps pulse sequence can achieve nonlinear ionization control and influence the induced ripples.

Based on Kogelnik’s coupled-wave theory, it is found that when a femtosecond pulse is incident on a transmitted volume holographic grating, two transverse standing waves along the grating vector direction will be generated inside the volume holographic grating (VHG). Due to field localization of two standing waves, they have two different velocities along the propagation depth. On the output plane of the VHG, femtosecond dual pulses are generated in both the diffracted and transmitted directions. Results show that the pulse interval is determined by the refractive index modulation and thickness of the grating, while the waveform of the dual pulses is independent of the grating parameters.

Spatio-temporal coupling characteristics of ultrafast laser pulses are quantitatively tailored. An asymmetric microstructure is induced in the focal volume when the laser scans perpendicularly to the direction of the spatial chirp in fused silica. The tilted direction reverses when adding a Dove prism into the light path. The sign of the pulse front tilt can be turned from positive to negative by changing the group delay dispersion by steps. We reveal that the tilted direction of a microstructure depends on spatial chirp, and the interplay between spatio-temporal chirp leads to the change of tilted angles.