CO₂ laser resonant excitation of propylene molecules in diamond deposition using combustion-flame method

CO₂ laser resonant excitation of propylene molecules was investigated in propylene/oxygen (C₃H₆/O₂) combustion diamond deposition in open air. The wavelength of the CO₂ laser is 10.591 μm, while the central wavelength for the C-H vibration mode in propylene molecules is 10.684 μm. The absorption peak of this mode is broadened by the high ambient pressure and the flame temperature, and thus covers the CO₂ laser wavelength to enable the resonant absorption. The inner cone of the C₃H₆/O₂ flame became shorter and brighter with the CO₂ laser irradiation with a laser power of 800 W. The scanning electron microscopy (SEM) images showed that better crystal grains in the diamond films were deposited with the CO₂ laser excitation. The film thickness also had an obvious increase within the same deposition time, indicating a higher growth rate of diamond films. The effect of different positions where the laser irradiated the flames was also studied. It was found that the enhancement of the diamond growth was due to the balance of the generation and the dispersion of the beneficial radicals.