Imaging ultrafast evolution of subwavelength-sized topography using single-probe structured light microscopy

Abstract

Imaging ultrafast processes in femtosecond (fs) laser–material interactions such as fs laser ablation is very important to understand the physical mechanisms involved. To achieve this goal with high resolutions in both spatial and temporal domains, a combination of optical pump–probe microscopy and structured illumination microscopy can be a promising approach, but suffers from the multiple-frame method with a phase shift that is inapplicable to irreversible ultrafast processes such as ablation. Here, we propose and build a wide-field single-probe structured light microscopy (SPSLM) to image the ultrafast three-dimensional topography evolution induced by fs lasers, where only a single imaging frame with a single structured probe pulse is required for topography reconstruction, benefiting from Fourier transform profilometry. The second harmonic of the fs laser is used as the structured probe light to improve spatial lateral resolution into the subwavelength region of ∼ 478 nm , and the spatial axial and temporal resolutions are estimated to be ∼ 22 nm and ∼ 256 fs , respectively. With SPSLM, we successfully image the ultrafast topography evolution of a silicon wafer surface impacted by single and multiple fs pulses. The variable formation and evolution of the laser induced periodic surface structures during an ultrashort time are visualized and analyzed. We believe that SPSLM will be a significant approach for revealing and understanding various ultrafast dynamics, especially in fs laser ablation and material science.

Research progress of ultra-high spatiotemporally resolved microscopy

“…2016年Massaro等 [59] 图 6 (a) 莫尔现象及SIM实现超分辨原理 [56] ; (b) 基于DMD的结构光照明泵浦-探测成像系统光路图; (c) 左侧分别为硅纳米 线样品的SEM图像、SPPM成像、传统光学显微成像, 右侧为SPPM成像与传统光学显微成像分辨率对比、SPPM泵浦-探测获 得样品不同位置的载流子弛豫过程 [59] Fig. 6.…”

“…6. (a) Moire phenomenon and the SIM principle of super-resolution [56] ; (b) schematic of DMD-based structured pump-probe microscope [59] ; (c) the left side: SEM image, SPPM image, and image by conventional optical microscopy of silicon nanowire samples respectively; the right side: the carrier relaxation process at different positions of SPPM imaging and conventional optical microscopy imaging resolution and SPPM pump-probe [59] .…”

“…178701-23 2020年, 长春理工大学林景全团队 [115] 利用飞 超快NSOM [37] 20 nm 亚fs 可实现空间超分辨 系统复杂, 视场小, 成像速度慢 超快四波混频 AFM [26] 50 nm 10 fs 可实现空间超分辨, 可以得到 样品表面形貌信息 系统复杂, 视场小, 成像速度慢, 需要激发非线性效应 超快PiFM [42] 10 nm 200 fs 可实现空间超分辨, 可以得到 样品表面形貌信息 系统复杂, 视场小, 成像速度慢 超快STM [46] 0.1 nm 亚fs 可实现空间超分辨, 空间分辨 率最高 系统复杂, 视场小, 成像速度慢, 只适用导电样品 远场 多脉冲 高NA系统 [55] 接近衍射极限 fs 量级 速度快, 大视场 无法实现空间超分辨 SPPM [59] 114 nm fs量级 可实现空间超分辨 视场小, 需要多步相移, 成像速 度慢 SPSLM [60] 478 nm(横向); 22 nm (纵向) 256 fs 单帧成像, 大视场, 有三维成 像能力 无法实现空间超分辨 PINEM [67] 小于0.7 nm 10 fs 可实现空间超分辨 电子显微镜系统复杂, 设备昂贵, 样品要求高 超快PEEM [71] 10 nm 10 fs 可实现空间超分辨 电子显微镜系统复杂, 设备昂贵, 样品要求高, 空间分辨率受材料 影响 LRM [83] 接近衍射极限 10 fs 可获得SPP传播相速度和群 速度信息 目前仅能对SPP成像 远场 单脉冲 CUP [86] 1 µm 100 fs 帧数高, 成像速度快 压缩感知算法较复杂, 条纹相机 较为昂贵 OPR [87] 11.1 µm 100 fs 重建算法简单、直接、稳定性 好, 时间分辨率高 空间分辨率较低, 目前仅有微米 量级 CSMUP [88] 833 nm 4 ps 较高的空间分辨率, 图像尺寸 更大 时间分辨率依赖于高光谱相机光 谱带, 时间分辨率较低 STAMP [89] 1 µm 227 fs 在显微和宏观成像领域都适 用, 普适性强 帧数和时间分辨率存在依赖关 系, 难以兼得 FINCOPA [91] 3 物 理 学 报 Acta Phys. Sin.…”