A narrow line width optical parametric oscillator (OPO) (10) is used a pump for a tunable optical parametric oscillator to enable it to produce a mid and long wavelength IR output over a wide 5 20 micron bandwidth. The pumping OPO (10) is then set up to be non-colinearly phase matched. To enable the pumping OPO (10) to exhibit the narrow line width, it is seeded with a narrow line width seeding source. The result is output energy having an extremely narrow 4 nanometer line width. The narrowness of the pumping OPO (10) output is derived first by using non-colinear phase matching in the pumping OPO (10) and secondly by using seeding in the pumping of the pumping OPO (10).