DFWM reflectivity via two-photon free carrier generation in semiconductors in middle IR range A.E.Vidavskii, V.I.Kovalev, V.M.Raukhman. Lebedev Physics Institute , Leninski av . 53 , Moscow , Russia.ABSTRACT It's shown that the effect of two-photon free carrier generation (TFCG) in semiconductors is the most promising for achieving high DFWM reflectivities R with short enough decay time ¶ in wavelength range from 1 . 5 to >9 . 5 Un . The materials which allow to achieve R up to 100% with 't of order of nanoseconds for the range of interest are presented. Some specific features of DFWM via TFCG was studied experimentally in InSb at X= 10 . 6 Lm and in Ge at ?,= 2 . 91& FUn.