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1. Femtosecond laser polishing of germanium

   Taylor, L ; Xu, J ; Pomerantz, M ; Smith, T ; Lambropoulos, J ; Qiao, J ( November 2019 , Optical materials express)

   Freeform optics can reduce the cost, weight, and size of advanced imaging systems, but it is challenging to manufacture the complex rotationally asymmetric surfaces to optical tolerances. To address the need for disruptive, high-precision sub-aperture forming and finishing techniques for freeform optics, we investigate an alternative, non-contact polishing methodology using femtosecond lasers, combining modeling, experiments, and demonstrations. Femtosecondlaser- based polishing of germanium was investigated using an experimentally-validated twotemperature model of laser/germanium interaction to guide the understanding and selection of laser parameters to achieve near-nonthermal ablation for polishing and figuring. For the first time to our knowledge, model-guided femtosecond laser polishing of germanium was successfully demonstrated, achieving precision material removal while maintaining single-digit nanometer optical surface quality. The demonstrated femtosecond-laser-based polishing technique lays the foundation for semiconductor optics polishing/fabrication using femtosecond lasers and opens a viable path for high-precision, complex sub-aperture optical polishing tasks on various materials. © 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement 

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2. Femtosecond laser polishing of germanium [Invited]

   https://doi.org/10.1364/OME.9.004165  

   Taylor, Lauren L. ; Xu, Jing ; Pomerantz, Michael ; Smith, Thomas R. ; Lambropoulos, John C. ; Qiao, Jie ( October 2019 , Optical Materials Express)
3. Controlling Femtosecond Laser Ablation of Germanium for Laser Polishing Applications

   https://doi.org/10.1364/CLEO_AT.2018.AM1M.2  

   Taylor, L. L. ; Xu, J. ; Smith, T. R. ; Pomerantz, M. ; Lambropoulos, J. C. ; Qiao, J. ( January 2018 , Conference on Lasers and Electro-Optics, OSA Technical Digest)

   Sensitivity of femtosecond laser ablation to laser parameters was investigated to evaluate controllability of germanium material removal. A processing metric was determined, enabling a method to control laser polishing with flexible combinations of laser parameters. 

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4. Electrochemical Polishing of Extruded and Laser Powder-Bed-Fused Inconel 718

   https://doi.org/10.26776/ijemm.06.04.2021.04  

   Jain, Srishti ; Hyder, James ; Corliss, Mike ; Hung, Wayne NP ( October 2021 , International Journal of Engineering Materials and Manufacture)

   ABSTRACTElectro-chemical polishing (ECP) was utilized to produce sub-micron surface finish on Inconel 718 parts manufactured by Laser Powder-Bed-Fusion (L-PBF) and extrusion methods. The L-PBF parts had very rough surfaces due to semi-welded powder particles, surface defects, and difference layer steps that were generally not found on surfaces of extruded and machined components. This study compared the results of electro-polishing of these differently manufactured parts under the same conditions. Titanium electrode was used with an acid-based electrolyte to polish both the specimens at different combinations of pulsed current density, duty cycle, and polishing time. Digital 3D optical profiler was used to assess the surface finish, while optical and scanning electron microscopy was utilized to observe the microstructure of polished specimens. At optimal condition, the ECP successfully reduced the surface of L-PBF part from 17 µm to 0.25 µm; further polishing did not improve the surface finish due to different removal rates of micro-leveled pores, cracks, nonconductive phases, and carbide particles in 3D-printed Inconel 718. The microstructure of extruded materials was uniform and free of processing defects, therefore can be polished consistently to 0.20 µm. Over-polishing of extruded material could improve its surface finish, but not for the L-PBF material due to defects and the surrounding micro-strain. 

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5. Influence of laser polishing on fatigue life of conventionally machined and laser powder bed fusion 316L stainless steel

   https://doi.org/10.1016/j.mfglet.2022.07.083  

   Faue, P.J. ; Beste, L.-H. ; Richter, B. ; Agrawal, A. ; Klingbeil, K. ; Thoma, D. ; Radel, T. ; Pfefferkorn, F.E. ( September 2022 , Manufacturing Letters)