15 July 1999 Emission spectra and particle ejection during visible laser ablation of graphite for diamondlike coatings
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Abstract
We have investigated the emission spectra of a carbon plume generated from graphite by a visible pulsed laser for diamond-like coatings (DLC). The laser utilized was a 300- watt class copper vapor laser with a pulse duration of approximately 40 ns. To better understand the laser-target interaction, we have visualized plume dynamics near the graphite surface via Schelieren method. We found that the laser ablation process was accomplished with explosive material ejection during pulsed laser deposition (PLD). The ejection of material started at about 500 ns after the onset of laser pulse and lasted for about 10 microsecond(s) . The material ejection is very directional and introduced large amount of micro particulates in the DLC film. We have found that the use of a random phase plate to smooth the laser intensity profile effectively eliminated this ejection of material with additional advantage of higher coating rate. The spectra in the visible and UV of the plume emission were analyzed to correlate with DLC quality and coating rate. We have characterized the carbon plasma based on emissions from C, C2, C+, and C++ for laser peak intensities between 0.1 - 5 GW/cm2 and 0.8 GW/cm2. The kinetic energy of C+ was estimated to be approximately 20 eV at this optimized coating condition. We found that greater C+ kinetic energy at higher laser intensity does not necessarily produce better DLC. This process optimization enabled us to demonstrate a coating rate as high as 2000 micrometers -cm2/hr. The C2 swan-band emission from the plume was most pronounced in the optimized coating condition and was used as a process diagnostic tool.
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Jim J. Chang, William McLean, Ernest P. Dragon, Bruce E. Warner, "Emission spectra and particle ejection during visible laser ablation of graphite for diamondlike coatings", Proc. SPIE 3618, Laser Applications in Microelectronic and Optoelectronic Manufacturing IV, (15 July 1999); doi: 10.1117/12.352710; https://doi.org/10.1117/12.352710
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KEYWORDS
Pulsed laser operation

Carbon

Laser ablation

Plasma

Copper vapor lasers

Visible radiation

Particles

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