OH-absorption properties of the optical damage region in codoped In/Mg:LiNbO3 crystals with various Li/Nb ratios

OH-absorption properties of the optical damage region in a series of codoped In/Mg:LiNbO3 crystals with various Li/Nb ratios have been investigated. The OH−-associated vibrational peak at 3507 cm−1 is confirmed to occur in crystals with Li/Nb ratio of 0.94. For codoped In/Mg:LiNbO3 crystals with Li/Nb ratio of 1.05 and 1.20, the OH−-associated vibrational peaks are detected at 3536 and 3507 cm−1 as well. A new peak at 3518 cm−1 attributed to a (InNb)2−–OH−–(MgNb)3− defect center is revealed in crystals with Li/Nb ratio 1.38. When the “In–Mg threshold” concentration is reached, the optical damage resistance ability of codoped In/Mg:LiNbO3 crystals is greatly improved.