Ultrafast laser and electron pulses for high resolution imaging

激光以一种变革性的方式影响了科学、工程和医学。激光为基础研究开辟了新的途径，并产生了改变我们日常生活的实际成果。激光使新的工业过程和医疗成为可能，并引发了当今的信息时代。激光可以在前所未有的时间尺度上探索物质的新状态。激光系统产生强大的光束，可以亚波长精度定位，并使显微镜工具具有无与伦比的分辨率。如今，激光科学正朝着紧凑型和高效的光纤激光器发展。然而，光信号在光纤中的传播导致必须小心管理的非线性效应，特别是对于短持续时间的脉冲。光纤激光器的有效带宽抑制了持续几个光周期的脉冲的产生。在接下来的任务中，我们将探讨解决限制光纤激光系统使用的后一种效应所引起的问题的方法。我们的提案还将讨论如何使用结构合理的激光信号通过激光扫描光学显微镜和激光加速电子束进行高分辨率成像。 1.来自光纤激光系统的更短和更强的脉冲。我们将使用一对啁啾光纤布拉格光栅的腔设计来提高光纤激光振荡器发射的脉冲的能量。我们还将设计基于受激拉曼散射的放大器，以在放大过程中保持超短脉冲的带宽，从而使光纤激光系统与固体激光系统竞争。 2.激光扫描光学显微镜的超分辨技术。我们将使用复杂的模式形状和去卷积方法，将SLAM(开关激光模式)显微镜的分辨率极限推到远低于衍射极限的50 nm。SLAM可以用于光学显微镜中的任何类型的模式，其增强的分辨率不需要任何特定的激光样品相互作用，与大多数超分辨率方法相反。 3.利用径向偏振激光脉冲加速粒子。我们介绍了一种利用超快径向偏振激光脉冲的纵向电场分量直接加速自由空间电子的方案。我们将利用这一方案，通过超快电子衍射产生适合于高分辨率成像的电子束。我们将探索如何利用激光脉冲的时空整形来加速激光焦点上的带电粒子，从而产生微米级的对撞机。 这项研究计划将在适合学生培养的环境中实现。学生将从许多内部和外部合作以及与行业的互动中受益。

Lasers have impacted science, engineering and medicine in a transformative way. Lasers have opened new avenues for fundamental research and generated practical outcomes that have changed our daily life. Lasers have enabled new industrial processes and medical treatments and have triggered the present age of information. Lasers have allowed exploring new states of matter at unprecedented time scales. Laser systems generate powerful beams that can be positioned with sub-wavelength accuracy and have enabled microscopy tools with unmatched resolution. Nowadays laser science is moving towards fiber lasers that are compact and efficient. However propagation of optical signals in optical fibers leads to nonlinear effects that must be carefully managed, especially with pulses of short duration. The effective bandwidth of fiber lasers inhibits the generation of pulses of duration lasting a few optical cycles. In the coming mandate we will explore methods to resolve the issues raised by the latter effects that have limited the use of fiber laser systems. Our proposal will also address how properly structured laser signals can be used for high resolution imaging with laser scanning optical microscopes and laser accelerated electrons beams. 1. Shorter and more powerful pulses from fiber laser systems. We will use a cavity design with a pair of chirped fiber Bragg gratings to boost the energy of the pulses emitted by fiber laser oscillators. We will also design amplifiers based on Stimulated Raman Scattering to preserve the bandwidth of ultrashort pulses during amplification in order to make fiber laser systems competitive with their solid-state counterparts. 2. Superresolution in laser scanning optical microscopy. We will push the resolution limits of SLAM (Switching LAser Modes) microscopy well below the diffraction limit, down to 50 nm, using complex mode shapes and deconvolution methods. SLAM can be used with any type of modality in optical microscopy and its enhanced resolution does not require any specific laser sample interaction, contrary to most superresolution methods. 3. Particle acceleration using radially polarized laser pulses. We have introduced a scheme to directly accelerate electrons in free space using the longitudinal electric field component of ultrafast radially polarized laser pulses. We will exploit that scheme to produce electron beams suitable for high resolution imaging by means of ultrafast electron diffraction. We will explore how spatiotemporal shaping of laser pulses could be used to accelerate charged particles at laser focus in such a way as to produce a micrometer scale collider. This research program will be realized in an environment suitable for student training. The students will benefit from many internal and external collaborations, as well as interactions with industry.