The preparation procedure, the transmissivity, and the two-wave coupli
ng properties of copper-modified potassium sodium strontium barium nio
bate (KNSBN) crystals are reported. The Cu ions doped in KNSBN can for
m two deep energy levels. This means that they are able to act as cent
ers for free charge carrier stimulation and recombination. The two-wav
e coupling gain coefficient of KNSBN: Cu is two times larger than that
of KNSBN. The photofractive sensitivity of KNSBN: Cu is estimated to
be in the order of 10(-3) cm(2)/J.