Femtosecond laser cutting of paper

Femtosecond laser processing of paper materials was performed to identify effective laser parameters of the pulse energy and the number of irradiation pulses in laser cutting experiments using a confocal optical microscope observation of the processed structures. We knew the threshold values of the laser parameters and revealed their nonlinear dependence. From the nonlinear dependence, we found a condition that minimizes the total irradiation energy, which is the product of the pulse energy and the number of irradiation pulses. We performed groove processing on the paper surface under laser parameters that did not cut the paper materials. The ablation in the grooved area increased with increasing total irradiation energy. The amount of debris on and beside the groove was also simultaneously increased. The discoloration beside the grove increased with increasing total irradiation energy. The debris decreased dramatically after cutting, and a few discolorations were observed. Because the positions of the discoloration and debris roughly matched and the discoloration and debris decreased simultaneously when the paper was cut, it was thought that the discoloration was due to accumulated debris. As demonstrative additional experiments, we present that characters printed on paper by a printer can be removed with minimal damage by adjusting the laser parameters to near the processing threshold of the paper and laser cutting of Japanese paper, which is a naturally derived paper with a complex structure and composition, without any visible discoloration.