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We report a temperature tuned mid-IR generating system ranging from 5 to 12 µm by difference frequency mixing of output waves from two optical parametric oscillators (OPOs) in a silver gallium sulfide (AgGaS 2 ) crystal. One of the OPOs generate signal wave of 1.6 µm, while the other produced tunable radiation from 1.846 to 2.353 µm. The AgGaS 2 crystal is temperature tuned to allow phasematching for tunable output from 5 to 12 µm.

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Mid-infrared radiation in the 5-18-mum range has been obtained by difference frequency generation in a AgGaSe(2) crystal by pumping with the output of a type I LiNbO(3) optical parametric oscillator (OPO). Here we suggest the use of a LiTaO(3) retarder to achieve an orthogonal state of polarization between OPO outputs that are necessary for efficient pumping of a AgGaSe(2) crystal. Several tens of kilowatts of peak power near 8 mum and continuously tunable operation in the above range have been obtained.

Signal and idlers waves obtained from a Nd : YAG laser pumped KTP optical parametric oscillator (OPO) are difference frequency mixed in a ZnGeP2 (ZGP) crystal to generate radiation in the mid-infrared. The KTP OPO is operated in the type-II phase matching mode, and the extraordinary and ordinary waves are tunable from 1.76 µm to 2.36 µm and from 2.61 µm to 1.90 µm, respectively. The orthogonally polarized waves are difference frequency mixed in a ZGP crystal to generate mid-IR radiation tunable from 5 to 12 µm.