Characterization of two-color holography performance in reduced LiNbO₃:In

The two-color recording sensitivity S and the figure of merit M# are measured in a reduced and congruent LiNbO₃:In crystal of 2.2-mm thickness. The results are compared with those before reduction treatment. It is found that S increases by an order of magnitude through reduction treatment but the M# is unchanged. Measured values for S and M/# in the reduced crystal are found to be 3 × 10³ cm/J and 0.04, respectively, with a total writing intensity of 4.0 W/cm² at 780 nm and a gating intensity of 1.15 W/cm² at 488 nm. These values are close to those of near-stoichiometric LiNbO₃ crystals under similar recording conditions. We also show that photoconductivity plays an important role in the improvement of S in LiNbO₃:In.