Tunable far-infrared generation by difference frequency mixing of dye lasers in reduced (black) lithium niobate

Continuously tunable far-infrared radiation from 2 to 50 cm−1 has been generated in lithium niobate which was reduced in a H2, N2 atmosphere to render it highly absorbing. The efficiency of far-infrared generation by optical excitation of absorbing defects compares favorably with generation by the electro-optic effect in clear LiNbO3. Output powers of a few milliwatts were obtained without phase matching.