Optical second harmonic generation in sodium nitrite

This paper deals with optical second harmonic generation (SHG) in ferroelectric NaNO2 at 1.06 μm fundamental wavelength. The temperature dependence of SHG in the range between 30 and 200 °C is observed for five different radiation geometries, each corresponding to one of the five nonvanishing components of the nonlinear susceptibility χ(2). Measurements are performed on plane-parallel and wedge-shaped one-domain crystals and on plane-parallel multi-domain crystals. Information is obtained about the temperature dependence of the coherence length lc = λ/[4 (n(2) – n(1))], of χ(2), and of the domain structure. χ(2) shows a rather strong decrease already in the ferroelectric phase and in general a sharp drop at the Curie temperature. The influence of the domain structure on SHG is discussed in detail.