In the 7.7-39.6 cm(-1) range, we investigated for the first time refraction
and absorption spectra of AgGaSe2 and AgGa1-xInxSe2 crystals which allowed
us to compute a phase matching characteristic and efficiency values of dif
ference frequency generation with total laser intensity from 60 MW/cm(2) up
to 15 GW/cm(2) The maximum efficiency values were close to 1 x 10(-3). A p
owerful half-cycle pulse generation is proposed with the investigated cryst
als.