High energy femtosecond laser micromachining with hollow core photonic crystal fiber delivery

In this paper, we demonstrate a new way to deliver the high energy femtosecond laser with Kagome-type hollow core photonic crystal fiber for micromachining compared to the traditional free space laser delivery. To achieve the high coupling efficiency and overcome the nonlinear effect in the delivery, the coupling system is optimized and the fiber is vacuum pumped to less than 5 mbar. High delivery efficiency more than 90% is achieved. To our best knowledge, this is the highest efficiency of femtosecond laser delivered by Kagome type hollow core fiber. With vacuum pump, we lowered the nonlinear effect and make the laser beam have good beam profile and slightly pulse duration change even in the delivery of laser with the pulse energy of 100 μJ, average power of 20 W, and pulse duration of 234 fs. The whole system is also used to make micromachining of aluminum and stainless steel with good processing quality.