50-nanometer femtosecond pulse laser induced periodic surface structures on nitrogen-doped diamond

Ultrashort pulse laser interaction with nitrogen-doped type I-b diamond was investigated with near-infrared femtosecond laser pulses at repetition rates of 5kHz and 11MHz. High spatial frequency laser-induced periodic surface structures with periodicities of 50 and 200nm were generated perpendicular to the polarization of the electric field. The novel 50nm features are found to be due to a phase transition from crystalline diamond to a graphitic phase in contrast to the 200nm laser-induced periodic surface structures consisting still of crystalline material.