Development of Precise Femtosecond Laser Micromachining Processes for Metals and Electrospun Nanofibers.

摘要

Femtosecond pulse lasers have proven to be versatile for micro-scale ablation of a variety of materials with high quality machining due to minimal residual stress, heat affected zone, and melting. In addition, femtosecond laser is one of the non-cleanroom techniques that does not require masking, chemical reagents, and multiple steps. This simple and convenient micromachining technique enables machining of various materials in 3-dimensional geometry. However, some factors such as optical scattering, beam shape, and debris accumulation hinder the high quality of ablation.;In this dissertation, femtosecond laser was employed for the micromachining of electrospun nanofibers and metals. Optimization of a process for the high quality femtosecond laser machining was investigated. Femtosecond laser and electrospun poly(e-caprolactone) (PCL) nanofibers mesh interaction was analyzed by optical property measurements and the optical absorption and scattering coefficients were estimated. The specific energy required for ablating a unit volume of pure PCL nanofibers and polydimethylsiloxane-poly(e-caprolactone) (PDMS-PCL) core-shell nanofibers was measured. Material inherent optical properties including the ablation threshold fluence and the incubation coefficient of PDMS and PCL were estimated. Circular grooves were fabricated on aluminum, stainless steel 316, and Stellite 6 and circular disks were successfully machined from a thick section of Stellite. The tapered cross-section was detected from the Stellite disk and the tapering was minimized by varying pulse energy during ablation process. Moreover, a novel debris removal technique based on DC-dielectrophoresis (DEP) force was used to machine the linear and circular grooves on aluminum and the ablation depth and precision were compared with the gas jet debris removal technique.