Low electron density diagnostics: development of optical emission spectroscopic techniques and some applications to microwave induced plasmas

Optical emission techniques for low electron density plasma diagnostics are reviewed and their applications critically evaluated. In order to assess possibilities and drawbacks of reviewed techniques some of them are used to diagnose low-pressure and atmospheric pressure microwave induced plasma. Difficulties and advantages of applied techniques are demonstrated. Directions of future research in the development of low electron density diagnostic techniques and improvements of the existing ones are also pointed out.