Two single-mode diode lasers and AgGaS_(2) as a nonlinear medium are applied for difference frequency generation (DFG) in the mid-infrared spectral range between 4.9 and 6.5 μm. Phase matching is achieved by either temperature tuning or angle tuning of the crystal. Experimentally measured sets of input wavelengths λ_(s) and λ_(p), the resulting DFG wavelength λ_(i), and corresponding phase-matching temperatures or angles are compared with the calculated values derived by use of different Sellmeier equations and coefficients and temperature-dispersion equations dn/dT. Our results show that only specific combinations of previously published Sellmeier equations, coefficients, and temperature-dispersion equations are suitable for exact calculations of phase-matching parameters. These combinations reproduce our experimentally obtained phase-matching temperatures and angles with an accuracy of better than 5% and are therefore of fundamental interest for the design of a mid-infrared DFG spectrometer with AgGaS_(2) as a nonlinear medium.
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