A photonic nanojet is a highly concentrated laser beam observed in the vicinity of dielectric micro-objects such as glass micro-spheres. Thanks to the concentration of the beam beyond the diffraction limit, giving a spot with a width smaller than a half-wavelength, the incident power density can be multiplied by a factor larger than 200. Photonic jet obtained with microspheres has been applied successfully to material ablation. It has been demonstrated that the ablation on metal or glass can have a half-wavelength width using a common infrared nanosecond pulse laser. However, the spheres in contact with the sample are difficult to move to achieve an industrial process and are disturbed by the removed material at the beginning of the process. Recently we have shown that photonic nanojet obtained in the vicinity of shaped optical fiber tip is an alternative to overcome these limitations. Sub-micron etchings have been obtained on metals, semiconductors and ITO using multimode optical fibers with a numerically designed shaped tip. The possibility to perform not only ablation, but also to generate self-organized micro-peaks, has also been experimentally demonstrated. Besides the small size of the processed area, our talk will focus on the low energy required for material removal. Due to the high energy concentration, the required energy to ablate is already 20 times smaller than in a classical process. Finally, we will show how the energy coupling in the fiber is a parameter as important as the tip shape to decrease the energy required to reach ablation.
Sylvain Lecler, Robin Pierron, Grégoire Chabrol, Frédéric Mermet, and Joël Fontaine, "Low energy sub-micron laser machining using photonic nanojet with shaped optical fiber tip (Conference Presentation)," Proc. SPIE 10520, Laser-based Micro- and Nanoprocessing XII, 105200Y (Presented at SPIE LASE: February 01, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2291569.5751458170001.
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