Nano-spheroid formation on YAG surfaces induced by single ultrafast Bessel laser pulses

We report on single pulse ultrafast Bessel laser beam processing of YAG ceramic surfaces as a method for producing contamination-free submicron particles and size adjustable surface hemisphere structures of different curvature signs. The micro-machining process was performed in both air and liquid environments, leading to a variety of surface structures depending on the processing parameters. Particularly, a transformation of the surface structure morphology from micro-hole profiles to hemisphere extrusions was observed. The size of the hemisphere structure is found to be highly sensitive to laser parameters, such as pulse energy, pulse duration and beam focusing position. Through careful analyses of the influence of the laser pulse parameters, a precise regulation of the lateral diameter and height of the hemisphere structure was achieved. Large area hemisphere arrays with low standard deviation in size were fabricated. The detachment of the emerging structures and subsequent particle deposition can be observed in liquid environments when the height-diameter aspect ratio of the hemisphere exceeds a factor of 0.65. The Mechanisms for the formation and detaching of the hemisphere structure are discussed with cross-sectional and morphology imaging via Scanning Electron Microscopy and Atomic Force Microscopy. As a preliminary step towards submicron particle generation in liquid environments, the observation of surface hemispheres has interest in exploring the initial mechanisms of particles formation under laser ablation in liquids. The presented method allows for the fabrication of contamination-free and size adjustable YAG submicron convex structures which have potential applications in integrated optics, biotechnology and other advanced processing techniques.