Three-dimensional shear stress measurement of stress waves in silica glass induced by a femtosecond laser

Laser-induced stress waves play a crucial role in ultrashort pulse laser (USPL) processing such as laser shock peening. However, previous studies have primarily relied on numerical simulations or two-dimensional measurements, lacking experimental validation of the three-dimensional stress distribution. This study presents what we believe to be a novel optical measurement technique to quantify the three-dimensional axisymmetric shear stress distribution of laser-induced stress waves using time-resolved circular polariscope imaging and integrated photoelasticity. Femtosecond laser pulses were used to generate stress waves in silica glass, and the induced birefringence was captured using a polariscope. The slow-axis angle and the optical retardance were extracted and used to reconstruct three-dimensional distribution of the shear stress component. The reconstructed stress distribution agrees with theoretical predictions and numerical simulations of a previous study. Additionally, we found that higher pulse energies resulted in broader stress wavefronts. This behavior is attributed to the expansion of the ablation region, which alters the wavefront shape. The ability to visualize and quantify the shear stress in three dimensions offers a more comprehensive understanding of stress wave interactions with materials. This study lays the foundation for further advancements in USPL processing and experiments utilizing USPL-induced high pressure.