Improved spectral resolutions were achieved in laser-induced breakdown spectroscopy (LIBS) through generation of
high-temperature and low-density plasmas. A first pulse from a KrF excimer laser was used to produce particles by
perpendicularly irradiating targets in air. A second pulse from a 532 nm Nd:YAG laser was introduced parallel to the
sample surface to reablate the particles. Optical scattering from the first-pulse plasmas was imaged to elucidate particle
formation in the plasmas. Narrower line widths (full width at half maximums: FWHMs) and weaker self-absorption were
observed from time-integrated LIBS spectra. Estimation of plasma temperatures and densities indicates that high
temperature and low density can be achieved simultaneously in plasmas to improve LIBS resolutions.
Fast growth of diamond crystals in open air was achieved by laser-assisted combustion synthesis through vibrational
excitation of precursor molecules. A wavelength-tunable CO2 laser (spectrum range from 9.2 to 10.9 μm) was used for
the vibrational excitation in synthesis of diamond crystals. A pre-mixed C2H4/C2H2/O2 gas mixture was used as
precursors. Through resonant excitation of the CH2-wagging mode of ethylene (C2H4) molecules using the CO2 laser
tuned at 10.532 Μm, high-quality diamond crystals were grown on silicon substrates with a high growth rate of ~139
μm/hr. Diamond crystals with a length up to 5 mm and a diameter of 1 mm were grown in 36 hours. Sharp Raman peaks
at 1332 cm-1 with full width at half maximum (FWHM) values around 4.5 cm-1 and distinct X-ray diffraction spectra
demonstrated the high quality of the diamond crystals. The effects of the resonant excitation of precursor molecules by
the CO2 laser were investigated using optical emission spectroscopy.
KEYWORDS: Diamond, Carbon dioxide lasers, Molecules, Combustion, Emission spectroscopy, Molecular lasers, Gas lasers, Temperature metrology, Chemical vapor deposition, Thin films
Optical emission spectroscopy (OES) measurements were carried out to study premixed C2H4/O2 and C2H4/C2H2/O2
combustion flame for diamond deposition with and without a CO2 laser excitation. Strong emissions from radicals C2
and CH were observed in the visible range in all the OES spectra acquired. By adding a continuous-wave CO2 laser to
irradiate the flame at a wavelength of 10.591 μm, the common CO2 laser wavelength, it was discovered that the emission
intensities of the C2 and CH radicals were increased due to the laser beam induced excitation. OES measurements of the
C2 and CH radicals were performed using different gas combinations and laser powers. The rotational temperatures in
the flame were determined by analyzing the spectra of the R-branch of the A2Δ→X2Π (0, 0) electronic transition near
430 nm (CH band head). Information obtained from the OES spectra, including the emission intensities of the C2 and CH
radicals, the intensity ratios, and the rotational temperatures, was integrated into the study of diamond deposition on
tungsten carbide substrates for mechanism analysis of the laser induced vibrational excitation and laser-assisted diamond
deposition.
CO2 laser resonant excitations of precursor molecules were applied in combustion flame synthesis of diamond films. The
combustion flame was produced from a mixture of ethylene (C2H4), acetylene (C2H2) and oxygen (O2). A wavelength-tunable
CO2 laser with wavelength range from 9.2 to 10.9 μm was used for wavelength-matched excitation of the
ethylene molecules. By irradiating the flame using CO2 laser at 10.532 μm, the ethylene molecules were resonantly
excited through the CH2 wagging vibrational mode (ν7, 949.3 cm-1). Irradiation of the flame using the common CO2 laser
wavelength at 10.591 μm was also carried out for comparison. It was found that diamond synthesis was more obviously
enhanced by the CO2 laser resonant excitation at 10.532 μm as compared to that at 10.591 μm. Firstly, the flame was
shortened by 50%, indicating a promoted reaction in the process. Secondly, the diamond grain sizes as well as the
diamond film thicknesses were increased by 200~300% and 160% respectively, indicating a higher growth rate of
diamond films. Finally, Raman spectra of the diamond sample showed a sharp diamond peak at 1334 cm-1 and a
suppressed G-band, indicating higher diamond quality.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.