Infrared diode laser absorption spectroscopy was used for measuring CFX (X=1-3) radical densities in electron cyclotron resonance plasmas employing C4F8, C2F6, CF4, and CHF3 gases commonly used for the plasma etching of silicon dioxide. CFX (X=1-3) radical densities in these plasmas were measured systematically together with CHF3 and CF4 molecular densities as a function of microwave power and as a function of H-2 dilution. Furthermore, variations of F atom densities in these plasmas were also investigated by the actinometry technique. The differences in the radical and atomic densities according to fluorocarbon feed gases are discussed based on their molecular structures and atomic component ratios (carbon/fluorine and hydrogen/fluorine).