Relationship of the second order nonlinear optical coefficient to energy gap in inorganic non-centrosymmetric crystals

Abstract

Second order nonlinear optical coefficient and energy gap data collected from the literature have been classified and are organized by plotting their respective values. The two-dimensional plots indicate that both large energy gap and small ζ (2) and small energy gap and large ζ (2) are highly correlated. It was found that a single law expression cannot represent the data well for energy gaps over the entire range from 0 to 10 eV. Therefore a fit for narrow energy gap (0 < 1 eV) and for wide energy gap ( E > 1 eV) materials are provided. A corresponding trend and fitting strategy is also demonstrated for the figure of merit (FOM) which is used to rank materials for wavelength conversion efficiency. Results of the analysis are used to estimate the second order nonlinear optical properties and conversion efficiencies of several less-well-known materials. Trend analysis suggests that ordered GaInP 2 would be exceptional as an E-O waveguide material and that the FOM of AgGaTe 2 is 3.3 times that of AgGaSe 2 and that crystals of HgGa 2Se 4 and Te x Se (1 − x) alloys should be of distinct interest as wavelength conversion materials for infrared applications. The maximum attainable ζ (2) is in the range of 3500–4000 pm/V for bound electrons. For energy gaps less than one eV, the increase in ζ (2) with decreasing energy gap slows considerably.