We present a method of resolving the nuclear and electronic contributions to the third-order susceptibility χ3 in a phase conjugation experiment. The technique is applied to octylmethylpolysilane yielding χ3 (electronic)=(1.8±0.5)×10-12 esu and χ3(nuclear)=(1.1±0.4) ×10-12 esu at 532 nm.
