Abstract

There has been considerable interest the past two decades in using lithium niobate (LiNbO₃) to generate the second harmonic of the 1.06-μm output of Nd:YAG lasers. Unfortunately, index inhomogeneities are induced in the LiNbO₃ from the resulting 0.53 μm, and it has been generally assumed that these inhomogeneities would drastically reduce SHG conversion efficiencies. Considerable work has therefore gone into the growth of noncongruent LiNbO₃ which phase matches above the self-annealing temperature (~180°C) for such induced inhomogeneities. More recently, work has been undertaken on growing MgO-doped LiNbO₃ which has improved resistance to the occurrence of index inhomogeneities. Both approaches present difficult material growth problems, however. In this paper we report on the utilization of congruent, easily grown LiNbO₃ to efficiently produce the second harmonic of 1.06-μm. A flashpumped Q-switched Nd:YAG laser was operated at 20 pps, multitransverse mode, with a 1.06-μm average output power of 2.0 W. Using a 9-mm long congruent LiNbO₃ crystal held at its phase-matching temperature of 0°C, we have obtained a 0.53-μm output of 1.04 W. Index inhomogeneities do occur in the LiNbO₃, but they saturate in the vicinity of the beam thereby allowing efficient SHG to occur. The result of other SHG experiments utilizing various LiNbO₃ crystal lengths and incident 1.06-μm power densities will be reported. For comparison, SHG experiments were also carried out on LilO₃, CD*A, KD*P, KTP, and MgO-doped LiNbO₃ crystals and are described.

© 1985 Optical Society of America