Internal modification of bulk polymer by continuous-wave laser backside irradiation

A spot of high heat-emitting bright light propagates toward the light source in optical fiber when a high-power laser beam is transmitted in the fiber. This phenomenon is called fiber fuse and damages the fiber. We demonstrated the fiber fuse phenomenon in bulk polymers and induced modification inside polymethyl methacrylate and polycarbonate sheets. Bright emission propagation was observed with a high-speed camera, and the propagation speed in the modified area was measured to be 6–70 mm/s. The modified area was 4 mm long and ~ 100 µm in diameter. The modified area was mostly filled with the modified polymer, and voids were observed in some cases. Energy-dispersive X-ray spectroscopy analysis revealed that the modified zone was composed only of C and O. The emission spectrum was similar to that of theoretical thermal radiation. The mechanism by which modification was induced was the same as that in a glass fiber fuse. The modification in polycarbonate was electrically conductive and the minimum conductivity per unit length was calculated to be 230 Ω/mm.