The role of fluorescence has not always been fully understood in optic
al engineering experiments that are devoted to the generation of phase
-conjugated waves from organic materials. It is pointed out that fluor
escence can appear if the material absorbs at the wavelength of the ex
citation. Therefore proper experimental precautions should be taken in
the detection of the intrinsic phase-conjugated signal. (C) 1996 Opti
cal Society of America