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Summary form only given. We describe an external-cavity diode laser (ECDL) seeded OPO based on bulk lithium niobate (LiNbO/sub 3/) and pumped at 1.06 /spl mu/m. A tunable ECDL operating in the range 1.50 to 1.59 /spl mu/m is used to injection seed a passive LiNbO/sub 3/ OPO ring cavity, producing widely tunable near-infrared radiation for various spectroscopic applications. Whereas our previous BBO OPOs were seeded at the nonresonant idler wavelength, this LiNbO/sub 3/ OPO is seeded at the resonant signal wavelength. As in the BBO OPO case, the cavity of the LiNbO/sub 3/ OPO is slightly misaligned to reduce its effective finesse, enabling it to be continuously tuned without mode hops over a range of several hundred GHz simply by scanning the ECDL seed wavelength. To characterize the output radiation and the seeding process, a part of the signal wave is mixed in KTP with residual pump radiation, producing radiation at /spl sim/620 nm by sum-frequency generation; the beam quality (e.g., spatial profile, coherence, pointing stability) of this visible radiation is viewed as the seed wavelength is scanned and its spectral purity is monitored by a pulsed wavemeter or etalon.