The second-order nonlinear optical coefficients are essential material parameters that determine the performance of nonlinear optical devices. Unfortunately, however, there have been considerable discrepancies among their absolute values reported to date [1]. This confusion, we believe, arises from the following factors. First, quite different values have been reported between parametric fluorescence (PF) and second-harmonic generation (SHG) measurements; e.g., d31(LiIO3) measured by PF method is 70 % larger than by SHG method [2. 3]. Second, wavelength scaling of nonlinear optical coefficients has been made based on the constancy of Miller’s Δ, although it has not been experimentally confirmed in what wavelength region and to what accuracy Miller’s Δ is constant. Moreover, the interference effect caused by multiple reflection effect in (nearly) plane-parallel samples has been overlooked in almost all the previous measurements, which can be the source of considerable error.
We have redetermined the absolute values of the nonlinear optical coefflcient, d31' of LiNb03 by parametric fluorescence and, for the first time, by difference frequency generation measurements to resolve the considerable discrepancy that existed between the values determined by second-harmonic generation (SHG) and parametric fluorescence. We obtain d31 =4.8~0.5 and 4.3~0.5 pm/V at the pump wavelengths of 488 and 532 nm, respectively, in reasonable agreement with the SHG data. It appears that the previous parametric fluorescence value, d31=5.8 pm/V, was overestimated.Key words : absolute measurement, second-order nonlinear difference frequency generation optical coefiicient, parametric fluorescence,
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