Figure 2

Schematic of a four- level molecular medium in a cavity with three layers (\({d}_{1}, { d}_{2},{ d}_{1}\)).The angle \(\theta \) is the incident angle of laser field upon the cavity well along the \(z\) axis, but \({S}_{r}\) and \({S}_{t},\) denote the reflected and transmitted GH shifts, respectively.