Abstract: According to plasma physical equations, the equation between the refractive index and the each components and temperature of arc plasma is deduced. Taking argon arc plasma as example, the refractive index has been calculated in varying temperature. The equation built provided a theoretic foundation for the diagnosing arc plasma by laser interferometry based refractive index effect. In this way, we can determine the arc plasma each of components and temperature through single-wavelength laser interferometry (included laser holographic interferometry) at the meantime, which can avoid many disadvantages of dual-wavelength method. The diagnosing arc plasma by single-wavelength laser interferometry plays an important role in developing technologies of arc plasma diagnosis and processing. The calculative result shows that refractive index is monotropic function of atomic density and electron density if wavelength is given; when temperature less than 6 000 K, electron has no effect on refractive index; When temperature more than 17 000 K, refractive index is completely determined by electron.

Key words: Laser interferometry, Plasma diagnostic, Refractive index, Single-wavelength