Application of a cw tunable infrared spectrometer based on difference-frequency generation in AgGaS₂ for self-broadening investigations of NO at 5 μm

A cw tunable infrared spectrometer based on difference-frequency generation in a nonlinear crystal of AgGaS₂ was constructed. An output wave-number range of 1920-2020 cm^-1 could be covered by an AlGaAs index-guided single-mode diode laser and a ring dye laser (dye: DCM). With an IR power of ∼15 nW and an emission linewidth of 30 MHz the self-broadening of the Λ doublet ²Π_3/2R(25.5) of NO in the fundamental band was investigated. The self-broadening coefficient γ = (0.0543 ± 0.0008) cm^-1 atm^-1 is compared with γ values for lower J″. The spacing of the Λ doublet was determined to be (5.5 ± 0.1) × 10^-3 cm^-1 which is slightly smaller than that given in the HITRAN database.