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.