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Lake Ronkonkoma, NY, United States

Tao S.,Advanced Optowave Corporation | Wu B.,Illinois Institute of Technology
Applied Surface Science | Year: 2014

Recent experiments in the literature have observed Coulomb explosion (CE) in metals under femtosecond (fs) laser irradiation. This is different from the previous common belief that CE will be strongly inhibited in metals due to the existence of a large number of free electrons with good mobility and the associated screening effect. It is still not well understood why CE can occur in metals. CE requires a sufficiently high outwards pointing electric field in the metal near-surface region. Using a physics-based model, this study shows that during the early stage of fs laser-metal interactions, the emitted electrons due to fs laser irradiation are still very close to the metal target surface, whose effects also need to be considered. The emitted electrons will generate an additional outwards pointing electric field in the target near-surface region, and will also exert a repulsive force on the electrons flowing from the deeper region of the target towards its surface. These effects are helpful to the development of a large outwards pointing electric field in the target near-surface region. The model calculation considering the effects of emitted electrons shows that the electric field at around the target surface can exceed the CE threshold under the studied conditions. The study has provided a physical explanation for why CE can occur in metals under fs laser irradiation. © 2014 Elsevier B.V. Source


Ye C.,Purdue University | Cheng G.J.,Purdue University | Tao S.,Advanced Optowave Corporation | Wu B.,Illinois Institute of Technology
Journal of Manufacturing Science and Engineering, Transactions of the ASME | Year: 2013

A magnetic field-assisted laser drilling process has been studied, where nanosecond laser ablation is performed under an external magnetic field. The study shows that the magnetic field-assisted laser drilling process produces deeper drilling depth and generates more confined plasma plume and relative less residual, as compared with laser drilling without magnetic field. This phenomenon has been rarely reported in the literature. The magnetic field effects on laser ablation have been analyzed analytically and a hypothesized explanation has been proposed based on the effect of the magnetic field on the plasma produced during laser ablation. Copyright © 2013 by ASME. Source


Zhang Z.,Southwest University | Liu Y.,Advanced Optowave Corporation | Xiong Z.,Southwest University
Plasmonics | Year: 2011

The transverse mode electron oscillations contribute to most of the surface-enhanced Raman scattering (SERS) intensity from the nanorod array substrates. To enhance the transverse mode electron oscillation and improve the SERS enhancements, the local electric field distribution of the orthogonal-nanorod structures, composed of two parallel horizontal nanorods in between two parallel vertical nanorods, has been studied. The local electric fields of the longitudinal mode along the horizontal nanorods act as the excitation for the transverse mode electron oscillations in vertical nanorods, leading to the cascade enhancements of the electric fields around the vertical nanorods. In addition, the plasmon peaks of the longitudinal modes can be tuned by changing the lengths and the widths of the horizontal nanorods and the separations between horizontal and vertical nanorods. These results would be much helpful to engineer SERS substrates to obtain larger SERS enhancements. © 2010 Springer Science+Business Media, LLC. Source


Dabir-Moghaddam N.,Illinois Institute of Technology | Tao S.,Advanced Optowave Corporation | Wu B.,Illinois Institute of Technology | Wu B.,Purdue University | Shin Y.C.,Purdue University
Manufacturing Letters | Year: 2016

Microholes with varying diameters at different depths are very desirable in various important applications. However, it is very challenging to produce microholes with varying diameters when the variation is in a complicated way and/or when the hole diameter is very small. This paper presents physics-based modeling work on the interactions among a picosecond (ps) laser pulse, a pre-existing plasma plume inside a microhole, and the hole sidewall. The modeling work implies the potential feasibility of a novel dual-pulse laser ablation and plasma amplification (LAPA) process for drilling microholes with varying diameters at different depths. © 2015 Society of Manufacturing Engineers (SME). Source


Zhou Y.,Electro Scientific Industries Inc. | Gao Y.,Illinois Institute of Technology | Wu B.,Illinois Institute of Technology | Tao S.,Advanced Optowave Corporation | Liu Z.,Illinois Institute of Technology
Journal of Manufacturing Science and Engineering, Transactions of the ASME | Year: 2014

This paper presents an interesting nanosecond (ns) laser-induced plasma deburring (LPD) effect (from microchannel sidewalls) discovered by the authors, which has been rarely reported before in the literature. Fast imagining study has been performed on plasma produced by ns laser ablation of the bottom of microchannels. It has been found that the plasma can effectively remove burrs from the sidewall of the channels, while on the other hand microscopic images taken in this study did not show any obvious size or shape change of the channel sidewall after LPD. LPD using a sacrifice plate has also been studied, where the plasma for deburring is generated by laser ablation of the sacrifice plate instead of the workpiece. The observed laser-induced plasma deburring effect has several potential advantages in practical micromanufacturing applications, such as high spatial resolution, noncontact and no tool wear, and less possibility of damaging or overmachining useful microfeatures when removing burrs from them. The fundamental mechanisms for the observed laser-induced plasma deburring effect still require lots of further work to completely understand, which may include mechanical breaking of burrs due to high kinetic energies carried by plasma and the associated shock wave, and/or thermal transport from plasma to burrs that may cause their heating and phase change, or other mechanisms. Copyright © 2014 by ASME. Source

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