Knowledge Bank

We have investigated the dependence of degenerate four-wave mixing (DFWM) spectra of gas-phase $I2$ on laser intensity, molecular transition moments and molecular concentration. The experimental results are interpreted by using a weak-field theory of DFWM derived with a density-matrix method. For comparison, the direct absorption spectra of $I2$ are also presented. We have demonstrated, in our observed DFWM spectra of $I2$, that the spectral resolution in DFWM can be better than that of linear optical spectroscopy. The outcome has also been elucidated by the theoretical result.