The application of DFWM to the gas flow measurement (spectral fitting of DFWM spectra)

We detect the DFWM spectra of iodine vapor seeded in argon gas at room temperature to examine the dependencies of DFWM spectra on pressure and input laser intensity. The spectral fitting is important to determine the temperature of the medium, but the DFWM spectrum depends not only on temperature but also on the other parameters such as input laser intensity, pressure and so on. In the present paper, the spectral fitting at various laser intensities and pressures is performed. In the relatively low pressure range {1-200 Torr(0.13-27 kPa)}, the DFWM spectra can be simulated well with two-level absorber model, introducing the corrections of decay rates and laser intensity. Above pressure of 300 Torr (40 kPa), the theoretical DFWM spectra including the line mixing effect agree well with the experimental ones.