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Summary form only given.Considerable work has been done to investigate the spectrum of the NO molecule and develop methods to measure trace concentration of this species. Detection of nitric oxide using tunable diode laser spectroscopy (TDLAS) has been previously reported. A sensitivity of 300 ppt was obtained, which demonstrated the potential of high-resolution infrared spectroscopy for NO detection. However, at present time, the absence of compact and room-temperature tunable infrared sources at NO absorption region (5.1 to 5.7 /spl mu/m) greatly limits the use of laser spectroscopy for potential applications. In this work, difference-frequency generation (DFG) is suggested as a convenient means to obtain such an infrared source, while periodically poled lithium niobate (PPLN) is selected as the nonlinear medium. Primarily, this material can be engineered for noncritical quasi-phase-matching of any combination of visible or near-IR lasers to produce DFG within its transparency range. It also features a large nonlinear coefficient and an optical transparency from visible to 5.4 /spl mu/m.