Strong stimulated cascade emission and coherent four-wave parametric r
adiations are observed. By proper observation of the excitation spectr
a, the cascade emission and the coherent four-wave mixing parametric p
rocesses can be identified. The effect of the buffer gas pressure on t
he intensity and the pulse compression of the emitted radiation were i
nvestigated. Cascade inversionless coherent radiation emission with ab
sorption reduction and third order nonlinear susceptibility enhancemen
t due to the presence of a strong internally generated field are discu
ssed for the 4p-4s strong emission observed. (C) 1996 American Institu
te of Physics.