Rehman Z U, Raza A, Qayyum H, Ullah S, Mahmood S, Qayyum A
Appl Opt. 2022 Oct 10;61(29):8606-8612. doi: 10.1364/AO.472340.
The shock waves generated during laser ablation of a copper target are investigated using the optical beam deflection method. The fluence of nanosecond pulsed infrared laser beam was in the range of 15-700/. The density jumps related with the influx of the shock wave at two interaction points were detected with the help of He-Ne laser probes. In general, a supersonic shock wave is produced, which propagates through air and gradually decays into an acoustic wave. Experiments were carried out to study the impact of laser fluence and propagation distance on the shock wave velocity and pressure. The shock wave velocity varies with laser fluence as ∝0.3 and with propagation distance as ∝. These results are compared with the predictions of the theoretical models. In the investigated fluence range, shock wave pressure rises by an order of magnitude (∼1-10). We demonstrated that shock wave pressure and ablated mass can be related, yielding mass-specific shock wave pressure that increases linearly with laser fluence. We have also noticed the shock-wave-induced probe beam focusing under certain conditions, which indicates that the shock wave modifies the refractive index of the compressed layer of air. The reported results are useful for the fundamental understanding and pave the way for new applications of laser-induced shock waves.
采用光束偏转法研究了铜靶激光烧蚀过程中产生的冲击波。纳秒脉冲红外激光束的能量密度范围为15 - 700 /。借助氦氖激光探测器检测了在两个相互作用点处与冲击波流入相关的密度跃变。一般来说，会产生一个超音速冲击波，它在空气中传播并逐渐衰减为声波。进行了实验以研究激光能量密度和传播距离对冲击波速度和压力的影响。冲击波速度随激光能量密度呈∝0.3变化，随传播距离呈∝变化。将这些结果与理论模型的预测进行了比较。在所研究的能量密度范围内，冲击波压力上升了一个数量级（约1 - 10）。我们证明了冲击波压力与烧蚀质量有关，产生了随激光能量密度线性增加的比质量冲击波压力。我们还注意到在某些条件下冲击波会导致探测光束聚焦，这表明冲击波改变了压缩空气层的折射率。所报道的结果有助于进行基础理解，并为激光诱导冲击波的新应用铺平道路。
