Efficient nonlinear frequency conversion using periodic reversals in the sign of the nonlinear coefficient to compensate for dispersion, quasi-phase-matching (QPM),1 can be accomplished in ferroeiectries with periodically inverted domains.2,3 In LiNbO3, QPM allows interactions between waves polarized along the z-axis, for which deff = 2d33 / π = 22 pm / V , as well as allowing interactions for which birefringent phasematching is impossible, e.g. SHG of blue light. First-order QPM requires sign reversals, and hence domain boundaries, separated by one coherence length, (lc =2.29 μm, 3.47 μm, and 6.31 μm for SHG of λ=467 nm, 532 nm and 660 nm radiation, respectively). The difficulty in this technique is the creation of the required finely spaced domains with sufficiently accurate periodicity. We have grown 0.8 mm diameter of 5% MgO-doped LiNbO3 crystals with these domain lengths by the laser heated pedestal growth method.4 To start the growth, a CO2 laser is focused on the tip of a source rod to make a small molten droplet into which an a-axis seed crystal is dipped. Domain reversal is achieved by periodically modulating the heating power which leads to a periodic variation in Mg concentration.
© 1991 Optical Society of AmericaPDF Article