We have proposed a one-dimensional optical forward phase-conjugate mirror w
ith the use of anisotropic self-diffraction in BaTiO3. A dynamic double-exp
osure interferometer has been constructed based on this diffraction algorit
hm, and we have demonstrated the application of this interferometer to opti
cal testing. The real-time measurement of the effective focal length of a p
ositive lens is demonstrated and both the theory and the experiment are pre
sented.