For the serious nonlinear optical loss, low output power density and non-flat light source in gas concentration measurement by a Cavity Ring-down Spectroscope(CRDS), a Raman laser by using Si as gain media was designed based on the nonlinear frequency shift mechanism of stimulated Raman scattering. To reduce the Two-photon Absorption (TPA) induced Free-carrier Absorption (FCA) and the FCA induced nonlinear optical loss in the silicon, a reversed p-i-n diode was designed to embed in a silicon waveguide.Then, the output power of Raman laser could be enhanced by controlling the voltage. In the experimental analysis, the reversed voltage was set to open, short, 5V and 25V, respectively, to observe the output power under the different voltages. The result indicates that the free carrier mobility time decreases from 16 ns to 1 ns and the output power increases outstandingly at the same condition, which enhances the reliability of gas concentration measurement.