Ultra-fast femtosecond (fs) lasers provide a unique technological opportunity to precisely and efficiently micromachine materials with minimal thermal damage owing to the reduced heat transfer into the bulk of the work material offered by short pulse duration, high laser intensity and focused optical energy delivered on a timescale shorter than the rate of thermal diffusion into the surrounding area of a beam foci. There is an increasing demand to further develop the fs-machining technology to improve the machining quality, minimize the total machining time and increase the flexibility of machining complex patterns on diamond. This article offers an overview of recent research findings on the application of fs-laser technology to micromachine diamond. The laser technology to precisely micromachine diamond is discussed and detailed, with a focus on the use of fs-laser irradiation systems and their characteristics, laser interaction with various types of diamonds, processing and the subsequent post-processing of the irradiated samples and, appropriate sample characterisation methods. Finally, the current and emerging application areas are discussed, and the challenges and the future research prospects in the fs-laser micromachining field are also identified.
The degree of laser-induced graphitisation from a sp 3 -bonded to a sp 2 -bonded carbon fraction in a single crystal chemical vapour deposited (CVD) diamond under a varying fluence of an ultrashort pulsed laser (30 fs, 800 nm, 1 kHz) irradiation has been studied. The tetrahedral CVD sp 3 -phase was 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 was formed. A fractional increase of fluence from 3.3 J/cm 2 to 3.9 J/cm 2 (~ 20 %) resulted in a substantial (~ three-fold) increased depth of the sp 2 -graphitised areas owing to the non-linear interactions associated with an fs-laser irradiation. Additionally, formation of C=O carbonyl group was observed below the critical threshold fluence; the C=O cleavage occurred gradually with the increase of irradiation fluence of 30 fs laser light. The implications for these findings on enhancement of fs-driven processing of diamond are discussed.
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