Observations of enhanced ion acoustic fluctuations in CO2 laser produced plasmas

The measurements demonstrate the existence of instabilities in an underdense plasma at power levels well below those required to excite stimulated Brillouin scattering and stimulated Raman scattering. Two additional excitation mechanisms, namely resonant absorption and the parametric decay instability are eliminated from consideration because of the sub-critical plasma densities at which enhancements are observed. It is significant to note that instabilities significantly affecting plasma properties can be excited at power levels well below those previously considered important for CO2 laser-produced plasmas. Although the instability mechanism producing the enhanced fluctuations has not been identified, these fluctuations have been shown to have a significant effect upon the thermal conductivity and absorptivity of the plasma.