Abstract

We have recently built a source that emits infrared radiation, tunable around 4.3 µm, by difference-frequency-generation (DFG) in periodically-poled LiNbO₃. 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 µm, we experimentally observed pattern formation [1], as a function of several parameters, like input wavelengths, crystal temperature, alignment of input beams with respect to the crystal, using a Nipkow disk [2], followed by a commercial single element liquid-N₂ cooled InSb detector. A numerical routine, that gives the three-dimensional evolution of the complex DFG field, during propagation of the two input beams in periodically-poled media, was also implemented. In Fig. 1 a comparison is shown of experimental data with results from the calculation. The good agreement between theory and experiment gives confidence into results from the program, that can be used in a wide range of input parameters.

© 2000 IEEE