Determination of the intensities of electric fields in gases and plasmas by the CARS method

A nonlinear optical method for nonperturbing local measurements of the intensity of electric fields in gaseous and plasma molecular media is proposed. It is based on the generation of coherent infrared radiation as a result of biharmonic laser pumping in a static electric field. Investigations are reported of the dependences of the intensity of infrared radiation, emitted by molecular hydrogen at the frequency of the Raman-active vibrational—rotational transition $Q(1)$($\upsilon = 0, J = 1 \to \upsilon = 1, J = 1$) in the ground electronic state $X^1\Sigma_g^+$ ($\lambda = 2.4$ $\mu$m), on the electric field and gas pressure. The weakest electric field which can be detected at a molecular hydrogen pressure of 1 bar is 20 V cm$^{-1}$. The capabilities of the method are illustrated by local electric field measurements in a corona discharge.