Full text loading...
Schematic of the experimental setup for pulsed laser ablation in gaseous, liquid and supercritical CO2. For the OES measurements, an optical fiber was placed in front of one viewport on axis with the target surface, whereas for shadowgraph imaging, the setup was switched and the ICCD camera and Xe flash lamp were positioned in front of opposite viewports of the high-pressure cell. The colored lines with arrows indicate the triggering setup for OES measurements (blue) and shadowgraph imaging (purple), respectively.
Optical emission spectra measured in CO2 at 0.1 (black curve) and 7.4 MPa (red curve). Both spectra were obtained by integration of 500 spectra taken with a gate delay and a gate width of 170 ns (0-40 ns after the laser pulse) and 10 ms, respectively. The dashed boxes indicate the domains of the spectrum where Ni lines are dominant. The first inset shows a close-up in the wavelength range between 235 and 255 nm, where peaks that can be attributed to atomic and ionized C can be found. The second inset shows the detailed spectrum in the region around 777 nm containing lines of atomic O.
Variation of the intensity and F D (dotted line) as a function of CO2 gas pressure. The change of the intensities of the Ni 471 nm (×) and O 496 nm () lines in CO2 for pressures between 0.1 and 16 MPa is shown.
Variation of line intensities and F D (dotted line) measured near the critical pressure of CO2.
Shadowgraph images taken in (a) liquid CO2 (6.30 MPa, 295.8 K) and (b)-(i) scCO2 (7.50 MPa, 304.5 K). (a) Generation of a cavitation bubble in liquid CO2. (b)-(i) Laser plasma formation and evolution of shockwave and cavitation bubble from 50 ns to 100 μs. (b) Target after laser pulse has disappeared. (c) Initiation of shockwave. (d) Formation of cavitation bubble and shockwave. The front of the shockwave and the cavitation bubble appear dark because of the difference in density between the CO2 medium. (e)-(f) Extension of shockwave and cavitation bubble, accompanied by the formation of smaller cavitation bubbles. (g) Disappearance of shockwave and contraction of cavitation bubble. (h) Cavitation bubble starts to emerge from the surface of the target. (i) Mixing of cavitation bubble with ambient CO2.
Article metrics loading...