Semiconductor laser etching of chicken eggshells: Process-structure relationships and microstructural damage

To reduce uncontrolled eggshell cracking during puncture of embryonated chicken eggs, this study investigated how etching with a 450 nm continuous-wave blue semiconductor diode laser affected processed-region geometry, microstructure, puncture-induced cracking, and hatchability. The laser-processed eggshells were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy coupled with SEM (SEM-EDS), X-ray diffraction (XRD), and Raman spectroscopy, as well as qualitative high‑speed imaging. Increasing the nominal laser power or decreasing the scanning speed increased the heat-affected zone (HAZ) width, material removal zone (MRZ) width, and etching depth. Changes in nominal laser power were accompanied by more pronounced changes in the local bottom-surface morphology, whereas changes in scanning speed were mainly accompanied by changes in the spatial dimensions and penetration depth of the processed region. XRD and Raman analyses showed that calcite CaCO₃ remained the predominant crystalline phase after laser processing, while weak CaO-related XRD reflections observed under more severe processing conditions indicated limited phase transformation. In the functional validation experiments, puncture-induced crack incidence decreased with increasing nominal laser power and increased with increasing scanning speed, whereas hatchability exhibited the opposite parameter-dependent trends. Puncture-induced crack incidence was strongly and negatively correlated with hatchability (Spearman's ρ = -0.943, P < 0.001). These findings demonstrate parameter-dependent relationships among laser-processing conditions, puncture-induced cracking, and hatchability within the investigated experimental conditions.