Dependence of Skin Ablation Depths on Er:YAG Laser Fluence

Triangulation and histological studies were made of skin ablation depths following skin treatments with a Fotona Dynamis Er:YAG laser system. The following laser handpieces were used in the study: Full beam handpieces R04 and R11; Stamping patterned handpieces PS01, PS02 and PS03; fractionated handpiece FS01 and c) Scanning fractional handpiece F22. The laser fluence (F) was found to be the major parameter that determines the ablation depth during Er:YAG skin treatments. Here, F=E/A, where E is the energy of the laser pulse, and A is the laser spot size area. Above the ablation threshold Fthr, the ablation depth (D) was found to grow approximately linearly with the fluence as D = K x (FFthr) where K ≈ 4 m.cm2/J. For the same fluence, ablation depths were within experimental error independent of pulse duration, pulse energy and spot size. With identical fluences, the ablation depths achieved with the full beam handpieces R04 and R11 were measured to be the same as those obtained with the patterned beam handpieces PS01, PS02 and PS03, and as well with the stamping fractionated handpiece FS01. This is due to the fact that the Fotona Dynamis patterned and stamping fractionated handpieces do not use any focusing optics to create smaller micro beams. Instead, the full beam is divided into smaller beams by a metal screen or diffractive optics. As a result, the fluence of each individual micro beam remains unchanged and is of the same top-hat spatial distribution of the full beam. Ablation depths achieved with the scanning fractional handpiece F22 were found to follow the same linear dependence on laser fluence.