An experimental study of the diagnostic potential of laser selective excitation spectroscopy for a potassium plasma

A thermally tuned -switched ruby laser of moderate power, with emission wavelength at 6939 Å, has been used to selectively excite the transition in the atoms of a pure potassium plasma of low degree of ionization produced in a hot cathode diode. A pulse of intensified spontaneous emission has been observed at 6939 Å, 6911 Å, and at a number of other wavelengths. The possibility of using this type of interaction for localized plasma diagnostics has been studied experimentally. It has been found that the intensified signal decay time decreases with increasing electron density, thereby providing a potential means for measurement of this parameter. In particular, it is shown that because of a saturation effect, the recorded signal characteristics depend to some extent on the laser parameters. A specially tailored laser performance is suggested as essential in order to overcome these problems and obtain signals which depend unambiguously on the plasma conditions.