Abstract
Spatially resolved recordings of the plasma emission in a narrow spectral band and the absorption of an He-Ne laser probe beam have been used to deduce the electron temperature and estimate the density in sparks produced by a Q-switched Nd laser in nitrogen, argon and helium at pressures from 0.5 to 4.5 atm. A uniform temperature decay with time constants of several hundred nanoseconds is observed in nitrogen and argon in the range of 5-1 eV, whereas in helium a secondary heat wave emerges from the initial breakdown zone approximately=150 ns after breakdown. The temperatures obtained are in good agreement with published spectroscopic measurements under similar conditions.

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