Ablation of sapphire was carried out with a femtosecond pulse laser operating at a wavelength of 775 nm and a pulse width of 150 fs in ambient air. The quality and morphology of the laser ablated sapphire surface were evaluated. The surface ablation threshold was found to decrease with increasing laser pulse number irradiating on the substrate surface, reaching a minimum constant level after about 50 pulses. This is believed to be due to an incubation effect which is attributed to laser induced defect formation. It was also shown that a single femtosecond laser pulse could produce sub-micrometer pit holes on the substrate surface, believed to be caused by the self-focusing effect of the air which exhibits non-linear effect under the high intensity laser beam. Under appropriate conditions, femtosecond pulse laser etching could produce high surface finish quality on sapphire. Potential applications of this micro-machining process include the fabrication of sapphire-based devices.

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