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Title: Time Resolved Shadowgraph Images of Silicon during Laser Ablation:Shockwaves and Particle Generation

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Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE. Administrator for National Nuclear Security Admin.Nonproliferation and National Security Program Direction
OSTI Identifier:
Report Number(s):
R&D Project: 675201; BnR: NN2001000
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physics: Conference Series; Journal Volume: 59; Related Information: Journal Publication Date: 2007
Country of Publication:
United States

Citation Formats

Liu, C.Y, Mao, X.L., Greif, R., and Russo, R.E. Time Resolved Shadowgraph Images of Silicon during Laser Ablation:Shockwaves and Particle Generation. United States: N. p., 2007. Web. doi:10.1088/1742-6596/59/1/071.
Liu, C.Y, Mao, X.L., Greif, R., & Russo, R.E. Time Resolved Shadowgraph Images of Silicon during Laser Ablation:Shockwaves and Particle Generation. United States. doi:10.1088/1742-6596/59/1/071.
Liu, C.Y, Mao, X.L., Greif, R., and Russo, R.E. Sat . "Time Resolved Shadowgraph Images of Silicon during Laser Ablation:Shockwaves and Particle Generation". United States. doi:10.1088/1742-6596/59/1/071.
title = {Time Resolved Shadowgraph Images of Silicon during Laser Ablation:Shockwaves and Particle Generation},
author = {Liu, C.Y and Mao, X.L. and Greif, R. and Russo, R.E.},
abstractNote = {},
doi = {10.1088/1742-6596/59/1/071},
journal = {Journal of Physics: Conference Series},
number = ,
volume = 59,
place = {United States},
year = {Sat Feb 03 00:00:00 EST 2007},
month = {Sat Feb 03 00:00:00 EST 2007}
  • Time resolved shadowgraph images were recorded of shockwaves and particle ejection from silicon during laser ablation. Particle ejection and expansion were correlated to an internal shockwave resonating between the shockwave front and the target surface. The number of particles ablated increased with laser energy and was related to the crater volume.
  • Plasma emission generated during a laser ablation event can saturate an imaging system, washing out valuable information about non-luminous features such as vapor plumes and shock waves. A step-by-step experimental history of development of imaging system from Shadowgraph to Monochromatic Schlieren is presented here as a method of resolving this issue. An ICCD system was used to image ablation events on {mu}s-timescales in combination with a fiber-coupled Nd:YAG laser operating at a primary output of 50 mW at 532 nm wavelength, which was used as the illumination source. A monochromatic band pass filter at 532{+-}10 nm was inserted into themore » Schlieren system between the focusing lens and the spatial filter, producing a minute shift in the Schlieren focus. With the filter, the saturation effects were eliminated and features such as shock waves and vapor plumes were clearly visible even when plasma was present. Issues with implementation of this system for application to the study of laser propulsion are discussed in detail.« less
  • Nanosecond time-resolved reflectivity and ellipsometry experiments have been performed on (100) Si wafers encapsulated by 5.5--76.2 nm thick thermal oxides, using pulsed KrF (248 nm) laser energy densities sufficient to melt the Si beneath the oxide. Post-irradiation nulling ellipsometry, optical microphotography, and surface profiling measurements were carried out. It was found that the threshold energy density required to melt the Si varies with oxide thickness; this is explained primarily by the reflective properties of the oxide overlayer. The time-resolved reflectivity and ellipsometry measurements show that rippling of the SiO/sub 2/ layer occurs on the 20--40 ns timescale and results inmore » a decrease in specular reflectivity of the rippled silicon surface beneath. Optical model calculations suggest that pulsed laser annealing through a thick oxide layer results in a damaged near-surface silicon layer (approx.30 nm thick); this layer contains defects that are probably responsible for the degraded performance of devices.« less
  • A technique has been developed for continuously carrying out time-resolved ellipsometric measurements on the nanosecond timescale. Using this technique, the optical properties of silicon have been measured during and immediately after pulsed excimer (KrF, lambda = 248 nm) laser irradiation. From these data the optical functions of liquid silicon at lambda = 632.8 nm have been determined to be n = 3.8 and k = 5.2 +- 0.1, in minor disagreement with the results of Shvarev, Baum, and Gel'd (High Temp. 15, 548 (1977)). The surface temperature before and after melting was also continuously determined by comparing these results withmore » elevated constant-temperature measurements of the optical functions. The results demonstrate that time-resolved ellipsometry is a powerful technique for examining changes in optical properties on the nanosecond timescale.« less
  • The dynamics of silicon solidification from the melt during pulsed-ruby-laser annealing have been investigated with the use of time-resolved electrical-conductance and optical-reflectance measurements. Melt duration was found to increase with laser-energy density to over 450 nsec at the highest energy used (3.1 J/cm/sup 2/). Resolidification velocity was found to vary with time and laser-energy density over a range of 2 to 3 m/sec. The melt threshold was observed to be 0.8 J/cm/sup 2/. Measurements of the laser energy absorbed in the sample were made to determine energy coupling parameters for use in numerical calculations. The numerical calculations, based on amore » thermal model for laser melting, are found to be in good agreement with the experimental results.« less