Abstract: In this paper we have intensively researched a seed Raman generator for excimer lasers. By adding a lightguide into the Raman cell,the Raman transfer can be enhanced. Furthermore,by blending the Raman medium hydrogen with certain amount of helium, we can control the energy transfer from the pump field to the first-order Stokes beam（S₁）.For pure hydrogen, we have obtained a peak conversion efficiency to S₁ η_max=37%. For H₂-He mixture with 5% He concentration,we obtained high conversion efficiency to S₁(η'≥ 95%η_max)in the range 50 to 80 mJ of pump energy,whereas the conversion to high-order Stokes was suppressed markedly.Finally,we made a theoretical analysis.