engleski

iCCD imaging VS laser induced breakdown spectroscopy in helium atmospheric pressure plasma jet

Here a comparison is shown between fast iCCD imaging and newly developed diagnostic method utilizing laser induced breakdown in a helium atmospheric pressure plasma jet. The plasma jet was powered by an 80 kHz high-voltage sine wave and propagated into the ambient air. Nd:YAG pulsed laser (4 ns pulse duration and 5 Hz repetition rate @1064 nm) was focused by a lens into the plasma jet at energy below breakdown threshold in helium. Laser and the plasma source were synchronized with the possibility to change the time delay between them. Depending on the time when the laser arrives, there is a different electron density in the laser focus at the laser pulse arrival. This affects the electron multiplication (avalanche) and the optical emission intensity of the laser induced plasma. We compared the radial profiles of the plasma jet obtained with these two methods. For the laser induced breakdown it was ±0.5 mm and for ICCD measurement it was ±1.75 mm, while the ionization wave velocities obtained with these two methods were 15 km s−1 and 20 km s−1 respectively. Electrical characteristics of the plasma jet were also presented and one can see a large hysteresis effect when the applied power to the plasma jet was reducing. We show that the laser induced breakdown spectroscopy can be used as a complementary diagnostics technique with ICCD measurements.

plasma jet, iCCD imaging, LIBS

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