Abstract

The first study of optical second-harmonic generation in the absorption band of an organic nonlinear crystal is presented. In our work, angle tuned Type-I phase-matching was achieved in the organic crystal DAN (4-(N,N-dimethylamino)-3- acetamidonitrobenzene) for fundamental wavelengths between 1000 nm and 950 nm from a CW dye laser. The generated wavelengths between 500 nm and 475 nm were well within the absorption edge of DAN, resulting in an absorption constant that varied between 21/cm and 10³/cm. For characterization purposes, the absorption in this wavelength range was studied in greater detail and a large dichroism with absolute transmission varying by a factor of 10⁷/mm was detected as the direction of propagation was changed. For a fundamental wavelength of 995 nm a detailed comparison of the achievable conversion efficiency was made between a 0.75 mm long DAN crystal and a 5 mm long crystal of KTP. At the generated 497.5 nm the DAN crystal had an optical density of 1.1, while the KTP was transparent. Despite the absorption and the smaller length of the crystal, a 4 times higher conversion efficiency was obtained than for KTP. Analysis of the data shows that the absorption band provides a significant resonant enhancement of the DAN nonlinearity. Similar results can be expected for other organic crystals provided phase-matching is possible.

© 1988 Optical Society of America