Ultrafast dynamics of three types of simultaneous shockwaves and filament attenuation in femtosecond laser multi-pulse ablation of PMMA

Cylindrical shockwaves inside polymethyl methacrylate(PMMA) generated simultaneously with two hemispherical shockwaves induced by a femtosecond Gaussian beam laser were investigated using an ultrafast pump–probe imaging technique. The evolutions of these three shockwaves with probe delay and incident pulse number have been systematically analyzed. The plasma intensity and filament length in the center of cylindrical shockwave both decayed with pulse number. Moreover, the self-focused filament moved downstream towards the output surface with an increased pulse number. The experimental results and mechanism illustrated that energy deposition was suppressed by a degraded nonlinear effect due to a pre-ablated structure in multi-pulse irradiation.     

新型磁强计实现原子尺度的结构分辨

<正>核磁共振在物理、生物及化学材料等领域具有重要的应用,而当前实现单分子核磁共振是此领域的一大挑战。中国科学技术大学杜江峰研究组及其合作者利用掺杂金刚石中氮-空位(NV)固态单电子自旋量子干涉仪,成功在室温大气环境下实现了单核自旋对的探测及其原子尺度的结构分析。具体而言,作者将动力学解耦序列作用在NV上,成功探测到距离其约1 nm处的单13C-13C对,刻画出两个核