In optical plasma diagnostics, line intensity ratio method is one of method to determine electron temperature and density of plasma. The intensity of radiation, Iki, is expressed by
Eki : Difference between energy levels Ek and Ei (Ek>Ei)
Aki : Transition probability
Nk : Population of upper energy state of k.
Line intensity ratio of plasma is expressed by
: Wavelength corresponding to the transition from energy state k to energy state i.
In experiment, the optical system cannot collect whole radiation from plasma volume, the transmittance of optical system has a dependency on wavelength, and quantum efficiency of detecting system is also dependent on a wavelength. Thus, the measured line intensity ratio needs to be relatively calibrated for whole optical system and detector.