constant maintenance and alignment. Early efforts at using solid-core fibers to
deliver high-power CO
2
beams have suffered from thermal damage, particularly
at the air–fiber interfaces at the input or the output end of the fiber [71–73].
Some of the promising solid-core fibers also suffered from short lifetimes because
of degradation of the guiding material when carrying high-power laser beams
[71]. To overcome these problems, researchers started to investigate high-power
CO
2
laser delivery systems based on hollow-core fibers.
Initial attempts based on rectangular and circular metal-coated hollow-core
fibers succeeded in transmitting up to 3 kW of laser power [74, 75]. However,
these power levels were achieved with fibers having large core radii, which ...