Investigation of laser pulsing parameters’ importance in Er:YAG laser skin ablation: a theoretical study conducted via newly developed thermo-mechanical ablation model

Abstract

Objective: Importance of laser pulsing parameters and tissue’s mechanical properties in the Er:YAG laser skin-tissue ablation is not adequately understood. The goal here was to develop a computational model that incorporates skin tissue’s mechanical properties to investigate the influence of Er:YAG laser pulsing parameters on tissue ablation and coagulation.Methods: Tissue’s mechanical properties were incorporated by modeling ablation as a tissue water vaporization occurring under elevated pressures that depend on tissue’s stress–strain relationships. Tissue deformation was assumed unidirectional; therefore, a one-dimensional model was utilized. Analytical solution and experimental results were used to verify and validate the model. Then, influence of pulse duration (10 µs–2 ms) and fluence (0–30 J cm−2) on coagulation depth and ablation efficiency was explored.Results: Verification and validation results suggested that the model is acceptably accurate. Minimal effect of pulse duration on coagulation depth was predicted at sub-ablative conditions. At those conditions, coagulation depth increased asymptotically to ∼90 µm with increasing pulse fluence. At ablative conditions, coagulation depth decreased asymptotically to 22–28 µm with increasing pulse irradiance. Ablation efficiency plateaued at high pulse fluences and long pulse durations. Mechanical properties were important as about 50% increase in coagulation depth and 25% decrease in ablation efficiency were predicted when considering the high strain-rate loading effect in comparison with quasi-static loading.Conclusions: Proper tuning of Er:YAG laser pulsing parameters can substantially improve its therapeutic outcomes. The effect of these parameters varies and depends on whether the laser-tissue conditions are ablative or sub-ablative.