You can download two video clips showing LIBS plasma in air. Both clips
were taken simultaneously. "LIBS_Plasma.mov" is a close-up of the
plasma produced by the prototype ChemCam Mast Unit at a distance of 5
m. The sample was moved a distance of 50 cm along a track, showing that
the plasma produced by only the 15 mJ laser (no amplifier) was strong
enough to be insensitive to focal distance. The distance between the
camera and the sample was kept constant while the sample was moved.
"LIBS_Plasma_Video_Set-Up.avi"
shows how the first clip was made. It shows the sample and the camera
used for the first video being moved along the track. The 15 fps rate
misses a few of the laser pulses. Comparison with the close-up clip
shows this is an artifact of the camera. Note that the apparent
wandering of the plasma
position on the sample seen in the close-up clip is due to the motion
of the sample. There is no positional instability of the laser relative
to the spark size.
In a Martian atmosphere the size and brightness of the visible plasma
is greater than in the terrestrial atmosphere, as the lower pressure
allows greater expansion of the emitting plasma and reduced
self-shielding of the plasma results in greater sample ablation rates
(Knight et al., 1999).
LIBS_Plasma.mov requires Quicktime to play, downloadable free from Apple.com.
LIBS_Plasma_Video_Set-Up.avi requires Real Player or a similar Windows
video player.
