Microsecond Pulsed Laser Material Ablation by Contacting Optical Fiber

The conditions that allow productive material ablation via contacting fiber, delivering microsecond pulses of Nd:YAG laser without damage of the fiber tip, are found. Stomatologic materials such as ceramics, composites and metal alloys were used as targets in atmospheric air. The choice of materials is caused by high potential of contacting fiber ablation technique in dentistry. Silica fiber with core diameter of 300m was positioned at distances =0-1mm from the target surface. Pumpprobe laser shadowhraphy allowed to study the material plasma expansion dynamics and peculiarities (size, speed, direction of motion) of the target microparticles ejection. Two types of fiber tip damage were studied: catastrophic (mechanical destruction preventing further ablation) and acceptable (enhanced light absorption and scattering by the target material deposited on the fiber accompanied by the tip surface low rate etching by laser beam with formation of a minor negative lens). It is shown that for laser fluencies E20-40J/cm 2 , when microsecond pulsed materials ablation rates are quite high (~1-10m/pulse), for the investigated targets no catastrophic damage of contacting fiber tip occurs for all gaps and laser pulse number N10 3 -10 4 , excluding metal case with 10-20m.