1.06-0.53-μm second harmonic generation using congruent lithium niobate

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.