Nonlinear Optical Property of Sodium Nitrite. I. Second Harmonic Generation at Room Temperature

The nonlinear susceptibility describing second harmonic generation in ferroelectric NaNO 2 at fundamental wavelength 1.153µm was measured with a continuous wave He-Ne laser by a phase matching technique. An ambiguity in choice of signs of effective nonlinear coefficients measured leads to four sets of tensor components and | d 16 |=| d 21 |=(0.174±0.049) d 36 (KDP) and | d 23 |=| d 34 |=(3.367±0.012) d 36 (KDP) are chosen on the basis of the Miller law. The signs of d 21 (= d 16 ) and d 23 (= d 34 ) are opposite. The nonlinear polarizability of a nitrite ion was found to be |β 16 (NO 2 - )|=|β 21 (NO 2 - )|=(0.39±0.11)·10 -23 cm 3 d 36 (KDP), |β 23 (NO 2 - )|=|β 34 (NO 2 - )|=(6.40±0.23)·10 -23 cm 3 d 36 (KDP), and |β 22 (NO 2 - )|=(0.56±0.14)·10 -23 cm 3 d 36 (KDP). The anisotropy of the linear and nonlinear susceptibility is ascribed to a π-electron system within the nitrite ion.