Bipolaron recombination in conjugated polymers J. Chem. Phys. 135, 074902 (2011) Correlation effects on the dynamics of bipolarons in nondegenerate conjugated polymers J. Chem. Phys. 130, 234908 (2009) Acidification of three-dimensional emeraldine polymers: Search for minimum energy paths from base to salt J. Chem. Phys. 128, 234903 (2008) Transformation of polarons to bipolarons in disordered matter Appl. Phys. Lett. 92, 222108 (2008) A suitable model for emeraldine salt J. Chem. Phys. 128, 174706 (2008) Additional information on J. Appl. Phys. The nonlinear absorption (NLA) was studied by open-aperture Z-scan experiments in the chemically reduced nominally pure LiNbO 3 crystals at cw-illumination with the red (644 nm) and green (514.5 nm) laser beams. The magnitude of the measured NLA is considerably different from the reported Z-scan results obtained in as-grown LiNbO 3 . The positive sign of NLA obtained with the red light has been related to the generation of the small bound polarons absorbing in red and near-IR ranges. Application of green light results in the light-induced transparency, i.e., the Z-scan traces show negative sign of NLA. Intensity dependence of Z-scan traces allows for conclusion that the photo-induced dissociation of small Nb Li 4þ :Nb Nb 4þ bipolarons and sequent generation of small polarons gives the dominating contribution to the nonlinear optical absorption in reduced crystals with a large bipolarons concentration. V C 2012 American Institute of Physics.