Laser Roughing of PCD

Femtosecond laser micromachining of diamond: Current research status, applications and challenges

“…There is a considerable difference between the optical absorption of a short-pulse, such as a nano-second and a pico-second (i.e., ns and ps, respectively) and an fs-pulsed laser radiation in diamond [29]. The laser energy absorption in pure, single crystal diamond (SCD) occurs through the electronic excitation across the  -* bond forming an exceptionally wide bandgap, E g , which depending on crystallinity, varies between 5.0 and 5.5 eV [15]. The E g can only be bridged by high energy UV photons ranging from approximately 250 nm (for a 5.0 eV E g ) down to ~ 225 nm (for 5.5 eV) diamond crystals.…”

“…However, conventional laser ablation systems normally use a visible 532 nm (green) or a near infra-red (N-IR) 1064 nm light for laser machining processes and, as a result, are unable to sublime pure diamond efficiently. Ablation in diamond is strongly affected by the presence of intrinsic and extrinsic defects including ad-atoms, interstitial or substitutional defects in the crystal lattice, point, line (e.g., grain boundary), volume and surface defects [15]. These defects collectively reduce the TF, whereas high defect concentrations are associated with low ablation TFs in diamond, which is advantageous for laser machining.…”

“…These defects collectively reduce the TF, whereas high defect concentrations are associated with low ablation TFs in diamond, which is advantageous for laser machining. In an instance when defects/impurities are absent altogether, multiple photons are able to excite an electron in a process known as multiphoton absorption, resulting in improved ablation rates [15], the latter, requires a high spatial and temporal photon density of an fs-pulsed laser with a focused beam [29]. Ramanathan et al [33] reported that even though the optical transparency of diamond is quite high for a vis -N-IR laser light, high peak power enables a stable absorption through a multiphoton ionization and absorption at defects in diamond.…”

“…The availability of synthetic diamonds in different grades (i.e., 'a' and 'b' grades), in various degrees of crystallinity, purity, degrees and types of doping, physical shapes and forms and, subsequently, at highly varied prices, made synthetic diamonds both more attractive and more economically accessible for a wide range of industrial applications compared to their natural counterpart [12,13], including the applications where diamond and its derivatives are used as machining tools [14]. The advantage of using tailor-made diamond products lies in its exceptionally high mechanical hardness that originates from directional sp 3 -hybridised bonds arranged in tetrahedral configuration that compose a single crystal [15]. It is the world's most desirable, albeit most notoriously known as 'hardest-to-machine' material, since there are no conventional material removal processes (MRPs) that are capable to effectively shape diamond crystals with an acceptable precision and accuracy at the nano-or micro-scale.…”

“…A number of MRPs have been employed to process diamond including electrical discharge [16,17] and abrasive waterjet machining [18], mechanical grinding [19], and laser machining [20,21]. These methods utilise the ability of diamond's intrinsic sp 3 -hybridised bonds to become converted, through externally applied energetic processes, into much weaker, sp 2 -hybridised bonds (as in graphite) and, after their subsequent removal, impart a final shape to the product [15]. Among these methods, laser machining (aka.…”