Spatial mode control of infrared radiation generated by difference frequency in periodically-poled crystals

Summary form only given. We have recently built a source that emits infrared radiation, tunable around 4.3 /spl mu/m, by difference-frequency-generation (DFG) in periodically-poled LiNbO/sub 3/. High resolution spectroscopic applications, like sub-Doppler spectroscopy, require a full control of the infrared spatial mode, during frequency scans. In spite of the difficulties inherent to recording of images at 4.3 /spl mu/m; we experimentally observed pattern formation as a function of several parameters, like input wavelengths, crystal temperature, and alignment of input beams with respect to the crystal.