The need to protect personnel from inadvertent eye trauma from fielded laser sources dictates that the highest externally accessible fluences produced by these systems be kept below the maximum permissible exposure (MPE) for intra-beam viewing. The large MPE value for a typical Q-switched (10 ns pulsewidth) source is 1 J/cm{sup 2} for wavelengths in the range of 1.5--1.8 microns, while the MPE for a similar pulsewidth Nd:YAG source is 5 {micro}J/cm{sup 2}. This 5 order of magnitude difference in the MPE is one reason for the trend towards shifting the output of near infrared sources used for remote sensing or ranging to the eyesafe wavelength region, even at the expense of overall system efficiency. There are 5 nonlinear optical crystals available with apertures of at least 10 x 10 mm{sup 2} which are also highly transparent in the 1.5 micron region; LiNbO{sub 3}, KNbO{sub 3}, KTP, KTA, and RTA. All 5 crystals are capable of 1,555 nm generation in an orientation with a favorable nonlinear optical coupling. However, KTP, KTA, or RTA are preferred materials, given that the generated signal of the OPO should remain at a fixed wavelength, insensitive to angular or thermal variations. The authors have characterized the …

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