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

The degree of laser-induced graphitization from a sp(3)-bonded to a sp(2)-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 sp(3) phase is found to transition to primarily an sp(2) aromatic crystalline graphitic fraction below the critical fluence of 3.9 J/cm(2), above which predominantly an amorphous carbon is formed. A fractional increase of fluence from 3.3 to 3.9 J/cm(2) (similar to 20%) results in a substantially (similar to 3-fold) increased depth of the sp(2) 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.