Enhancement of ablation efficiency by a femto/nano-second dual-beam micromachining system

In this paper, a dual-beam laser micromachining system consisting of a femtosecond (fs) laser and a nanosecond (ns) laser has been developed to enhance the ablation efficiency. Experiments were conducted in different materials including dielectric (fused silica), semiconductor (silicon wafer), and metal (aluminum alloys). The amount of material being removed was determined for fs pulses alone, ns pulses alone, and pairs of fs and ns pulses with different time lags in between. It was found that the material removal efficiency increases in the dual-beam process for all materials being studied as compared to the fs alone or ns alone, particularly for dielectrics. The highest ablation efficiency for fused silica occurs when the fs pulse is shot near the peak of the ns pulse envelope. A corresponding numerical model for dual beam ablation of dielectrics was also developed by integrating the plasma model, the improved two-temperature model, and Fourier's law to understand the laser-material interaction. It was found that the fs laser pulse can significantly increase the free electron density and change the optical properties of the dielectric, leading to the increase of absorption for the subsequent ns pulse energy. This study provides a fundamental understanding for the enhancement of material ablation efficiency, particularly for wide-bandgap dielectrics.

[1]  Lan Jiang,et al.  Energy transport and material removal in wide bandgap materials by a femtosecond laser pulse , 2005 .

[2]  Brent C. Stuart,et al.  Ultrashort-pulse laser machining of dielectric materials , 1999 .

[3]  T. Qiu,et al.  Short-pulse laser heating on metals , 1992 .

[4]  R. More,et al.  An electron conductivity model for dense plasmas , 1984 .

[5]  C. L. Tien,et al.  Femtosecond laser heating of multi-layer metals—I. Analysis , 1994 .

[6]  E. Campbell,et al.  Coulomb explosion in ultrashort pulsed laser ablation of Al 2 O 3 , 2000 .

[7]  B. Wolff-Rottke,et al.  Nanosecond and femtosecond excimer-laser ablation of oxide ceramics , 1995 .

[8]  G. Mourou,et al.  Femtosecond Optical Breakdown in Dielectrics , 1998 .

[9]  Norris,et al.  Time-resolved observation of electron-phonon relaxation in copper. , 1987, Physical Review Letters.

[10]  G. Gibson,et al.  ULTRAFAST ELECTRON DYNAMICS IN FEMTOSECOND OPTICAL BREAKDOWN OF DIELECTRICS , 1999 .

[11]  Cheng,et al.  Femtosecond room-temperature measurement of the electron-phonon coupling constant gamma in metallic superconductors. , 1990, Physical review letters.

[12]  B. Luther-Davies,et al.  Ablation of solids by femtosecond lasers: ablation mechanism and ablation thresholds for metals and dielectrics , 2002 .

[13]  Perry,et al.  Laser-induced damage in dielectrics with nanosecond to subpicosecond pulses. , 1995, Physical review letters.

[14]  S. Guizard,et al.  Measuring thermal effects in femtosecond laser-induced breakdown of dielectrics , 2002 .

[15]  M. Vičánek,et al.  Ultrafast dynamics of nonequilibrium electrons in metals under femtosecond laser irradiation , 2002 .

[16]  Xianfan Xu,et al.  Experimental and numerical investigation of heat transfer and phase change phenomena during excimer laser interaction with nickel , 1999 .

[17]  A. Tünnermann,et al.  Femtosecond, picosecond and nanosecond laser ablation of solids , 1996 .

[18]  Lan Jiang,et al.  Prediction of crater shape in femtosecond laser ablation of dielectrics , 2004 .

[19]  J. Meyer-ter-Vehn,et al.  Hydrodynamic simulation of subpicosecond laser interaction with solid-density matter , 2000, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[20]  Lan Jiang,et al.  Repeatable nanostructures in dielectrics by femtosecond laser pulse trains , 2005 .

[21]  M. Fox.  Optical Properties of Solids , 2010 .

[22]  M. El-Sayed,et al.  Laser-Induced Shape Changes of Colloidal Gold Nanorods Using Femtosecond and Nanosecond Laser Pulses , 2000 .

[23]  G. Reider,et al.  Two color laser ablation: Enhanced yield, improved machining , 2007 .

[24]  Koji Sugioka,et al.  Multiwavelength excitation by vacuum‐ultraviolet beams coupled with fourth harmonics of a Q‐switched Nd:YAG laser for high‐quality ablation of fused quartz , 1995 .

[25]  Wolf,et al.  Ultrafast electron dynamics at Cu(111): Response of an electron gas to optical excitation. , 1996, Physical review letters.

[26]  S. Fourmaux,et al.  Non-thermal melting in semiconductors measured at femtosecond resolution , 2001, Nature.

[27]  Perry,et al.  Nanosecond-to-femtosecond laser-induced breakdown in dielectrics. , 1996, Physical review. B, Condensed matter.