Femtosecond multistep laser etching of transparent amorphous organic film

Novel laser etching was demonstrated by one-shot femtosecond laser ablation of a transparent organic amorphous film. The etch depth increased stepwise with increasing laser fluence and each step is constant and independent of the fluence, while the number of steps and etching area increase with the fluence. The successive depths were 270, 480, 690 and 820 nm, for which the thresholds were 180, 180, 210 and 290 mJ/cm(2), respectively. A fifth step was not observed in the present fluence range. Both the etched surfaces an d slopes between the steps are very smooth with a roughness of less than 10 nm. The mechanism is proposed and discussed in view of the optical interfe rence effect and a possible application is mentioned.