Background and Objectives: High-resolution spectroscopy is known to need sources of coherent radiation in the mid- and farinfrared spectral bands. Sources based on optical nonlinear interaction (a difference-frequency generator and an optical parametric oscillator) are known to be almost ideally suitable for an application. Intracavity realizations of the devices with a nonlinear crystal located in the cavity, can likely be made simple, compact and easy to use.