Abstract
Responses of two types of single-crystal diamonds, prepared by chemical vapour deposition (CVD) and high pressure high temperature synthesis (HPHT) methods, respectively, to a nanosecond pulsed neodymium-doped yttrium aluminium garnet (Nd:YAG) laser were investigated and compared. It was found that due to the difference in the transmission rate and refractive index, the laser-induced surface/subsurface features of the two types of samples were distinctly different. For the CVD sample, destructive interference takes place on the upper surface, leading to direct ablation of smooth grooves with deposition of graphite. For the HPHT sample, however, laser-induced grooves were formed on the reverse side of the irradiation surface (namely, the lower surface) at certain laser fluences due to the constructive interference phenomenon of the laser and the high refractive index of the material. The reverse-side irradiation resulted in the formation of deep and sharp grooves with rough bottoms and insignificant deposition of graphite on the area surrounding the groove. The machining thresholds for the upper and lower surfaces of both types of diamonds were experimentally obtained and theoretically verified. The findings of this study provide important process criteria for laser machining of different kinds of diamonds. The reverse-side irradiation method enables efficient machining of deep grooves in diamonds using a lower power laser.
Highlights
Diamond is an important material having various applications, ranging from cutting tools to heat spreaders in light emitting diodes (LEDs) [1,2], due to its remarkable hardness, thermal conductivity and chemical inertness [3,4,5]
The laser used in the following experiments was a neodymium-doped yttrium aluminium garnet (Nd:YAG) laser pumped by a laser diode, LR-SHG, from MegaOpto Co., Ltd (Saitama, Japan)
Nanosecond pulsed Nd:YAG laser irradiation has been performed on two different types of diamond single crystals, one grown by chemical vapour deposition (CVD) and the other by high pressure high temperature synthesis (HPHT) synthesis
Summary
Diamond is an important material having various applications, ranging from cutting tools to heat spreaders in light emitting diodes (LEDs) [1,2], due to its remarkable hardness, thermal conductivity and chemical inertness [3,4,5]. These properties, combined with its high brittle nature, make diamond incredibly difficult to machine by conventional mechanical methods. Through the use of short pulses, high precision and sharp profiles can be achieved [7,9], as heat conduction into the bulk material is significantly reduced [10]. The machining of curved profiles with micron-sized curvatures has been shown to be possible by the use of femtosecond pulses and
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