Combining snapshot ultrafast imaging with 3D atomistic simulation: A new approach to explore laser ablation

Femtosecond laser ablation (FLA) plays an important role in the precision fabrication of materials with its evasive thermal effects and extremely precision. Recently, Prof. Shian Zhang and Prof. Yang Yang from East China Normal University combined a novel single-shot ultrafast imaging technique with molecular dynamics simulation method to jointly investigate the FLA process of bulky gold. The research results, published in “Ultrafast Science”, not only reveal the ablation mechanism of the material at different excitation energy flow densities, but also provide important guidance for the application of femtosecond laser ablation on other materials.

The novel single-shot ultrafast imaging technique used in this work is called chirped spectral mapping ultrafast photography (CSMUP), which uses a chirped laser pulse to actively illuminate the ablation scene and then uses a hyperspectral camera to acquire spectrally-resolved images. Finally, by virtue of the correspondence between the wavelength component and the time point of chirped probe laser, the time-resolved images can be acquired. CSMUP has been demonstrated to have an imaging speed of 250 billion frames per second, a spatial resolution of sub-micrometer, and a sequence depth of 25. Meanwhile, in theory, a large-scale 3D time-resolved simulations of the ablation process have been performed by using MD method. With detailed comparison analysis of the experimental results with the simulation results, the differences between the ablation morphology, temperature, pressure, and stress dynamics of the gold target under different excitation fluences are demonstrated.

At present, in the aspect of femtosecond laser ablation observation, the mainstream pump-probe technology can only obtain one frame of image at a time, thus the complete recording of the scene will be affected by the laser power jitter and the inhomogeneity of the material composition. In theory, two-temperature, hydrodynamics and molecular dynamics models can explain the basic mechanism of laser ablation process, but these simulation methods also have their applicability and limitations. Therefore, this research work is of great significance to achieve the analysis of the dynamic behavior and mechanism of femtosecond laser-material interaction by combining high spatial-temporal resolution single-shot ultrafast imaging technology with multi-model high-precision simulation tools.

This work not only provides a technical basis for monitoring the ultrafast laser fabrication in real time, but also is helpful for fully understanding the physical mechanism of the interaction between intense ultrafast laser and materials. In the future, the research method in this work will continue to be applied to the study of the femtosecond laser ablation of various materials.