Time-of-Flight Secondary Ion Mass Spectrometry Characterization and Elemental Distribution of Potassium Dihydrogen Phosphate Crystals Under Laser Irradiation

This study used time-of-flight secondary ion mass spectrometry (TOF-SIMS) to comprehensively analyze the elemental composition, ion distribution, and signal variations in potassium dihydrogen phosphate (KDP) crystals at various sputtering depths after laser irradiation. Positive ion mass spectra were employed to identify the characteristic ions K+, Ca+, Fe+, Si+, and P+. These ions were assigned to their corresponding chemical species. Large-area two-dimensional chemical mapping and maximum count/total count (MC/TC) analysis combined and showed clear depth-dependent trends; all detected ions had significantly higher MC and TC values at larger sputtering depths. At a depth of 1.3 nm, Fe-related and O-related ion signals exhibited overlapping localized hotspots, whereas Ca species showed ring-like enrichment at the edges of the damage pits. These changes are attributed to the laser-induced decomposition of KDP crystals, in which metal inclusions absorb laser energy, generate localized high temperature and pressure, and promote material ejection and ion redistribution. These findings provide direct experimental evidence for understanding laser-induced elemental redistribution in KDP crystals and offer useful guidance for further optimization of their performance.