CO2-TE laser produced cadmium plasma in vacuum experiment and kinetics

The rapidly transient character of the plasmas generated under the action of pulsed, high-intensity laser radiation may lead especially through relaxation processes to important deviations from the thermodynamic equilibrium distributions and sometimes to population inversions and lasing action. Related to the investigation of lasing action in the visible region, our results on laser emission at λ = 5378 A recombination line in CO2-TE laser produced cadmium plasma in vacuum, were previously reported. A detailed further study of the visible emission spectrum and the related parameters of the laser produced cadmium plasma are now presented. For the plasma production we have used a CO2-TE laser with a typical pulse shape (a peak of 200 nsec and a tail of 2 μsec). The analysis of the emission spectrum has put into evidence lines belonging to Cd I and Cd II species, but the presence of the recombination lines of Cd II ions indicates also the existence of Cd III ions in the plasma, in its early evolution stages at least. These lines were not directly detected because Cd III ions have not emission lines in the visible region. The plasma electron temperature was obtained using the ratio of the relative line intensities of subsequent ionisation stages, taking into account that for times between 0.2 and 1 μsec in its evolution, plasma can be considered in local thermodynamic equilibrium. (author) 5 refs., 1 tab