Raman study of the soft modification of graphene by femtosecond laser irradiation

Processing a graphene surface by irradiation with a fs-pulsed laser at energies below the ablation threshold allows the production of non-thermally modified regions with slightly different properties than pristine graphene. Oxidized nanoislands, optical forging, and nanopore networks are modifications of the graphene structure recently reported using a wide range of fs-laser energies. In this work, we first determined the pulse energy threshold of a fs-laser for the ablation of a commercial CVD graphene sample. Then we irradiated the sample in an extended range of pulse energies relative to the ablation threshold value. The irradiation process was simultaneously monitored by Raman spectroscopy, and the evolution of each Raman parameter (central position, bandwidth, and intensity) was analyzed. Special attention was given to the pulse energy that produced linear relationships between most Raman parameter pairs. These linear correlations evidence the interrelation between multiple Raman parameters and a soft processing method applicable to the controlled modification of the graphene lattice.