Laser-Induced Graphitization of Diamond Under 30 fs Laser Pulse Irradiation

The degree of laser-induced graphitization from a sp³-bonded to a sp²-bonded carbon fraction in a single crystal chemical vapor deposited (CVD) diamond under varying fluence of an ultrashort pulsed laser (30 fs, 800 nm, 1 kHz) irradiation has been studied. The tetrahedral CVD sp³ phase is found to transition to primarily an sp² aromatic crystalline graphitic fraction below the critical fluence of 3.9 J/cm², above which predominantly an amorphous carbon is formed. A fractional increase of fluence from 3.3 to 3.9 J/cm² (∼20%) results in a substantially (∼3-fold) increased depth of the sp² graphitized areas owing to the nonlinear interactions associated with a fs laser irradiation. Additionally, formation of a C═O carbonyl group is observed below the critical threshold fluence; the C═O cleavage occurrs gradually with the increase of irradiation fluence of 30 fs laser light. The implications for these findings on enhancement of fs driven processing of diamonds are discussed.