Femtosecond laser processing tailored for biomedical materials and laser power delivery through optical fibers

摘要

We have been working on the tailored ablation processing of advanced materials using femtosecond lasers. Here we would like to focus on the femtosecond laser processing tailored for hydroxyapatite. Hydroxyapatite is a key material of human tooth and human bone. The human bone is made of hydroxyapatite oriented along the collagen. The micromachining of human bone is highly required for medicine. The medical issue is how to preserve the chemical property of the laser-ablated surface. By use of pulsewidth tunable femtosecond laser (50fs ― 2ps, 1.5mJ, 1kpps), we compared the relative content of calcium and phosphorus. The relative content of calcium and phosphorus is kept unchanged before and after laser ablation. For these medical applications, the intense femtosecond laser delivery through optical fibers is required. It is theoretically shown that it is possible to deliver the 900 fs pulses of 0.1 mJ/pulse through a 1 m-long graded index fiber with a 200 μm core diameter if the fiber has the optimum refractive index profile. We therefore conclude that graded index multimode fibers give better spatial distributions of the output transverse mode than hollow fibers or step index multimode fibers, and can deliver larger pulse energy than single mode fibers.