Theoretical Evaluation on Terahertz Source Generators from Ternary Metal Chalcogenides of PbM₆Te₁₀ (M = Ga, In)

We develop a new method to calculate nonlinear optical (NLO) susceptibility and give a definition of the extended figure of merit (EFOM) contributed from optical susceptibility, refractive index, and absorptions to evaluate the material intrinsic property. The calculated phonon frequency determines the infrared absorption coefficient and transparent cutoff edge. We calculate the conversion efficiencies of the terahertz source generating from chalcogenides PbM₆Te₁₀ (M = Ga, In), based on difference frequency generation of optical process in terms of the EFOM and experiment parameters. The calculated terahertz light conversion efficiencies of PbGa₆Te₁₀ and PbIn₆Te₁₀ are in the order of 10^–3 to 10^–2 at low side of THz wavelengths, and the conversion efficiency of PnIn₆Te₁₀ is larger than that of PbGa₆Te₁₀ at the same conditions. A small terahertz wavelength and absorption coefficient and a large nonlinear susceptibility, that is, a large EFOM will result in a large conversion efficiency. These studies give an indication that the chalcogenides with heavy element composites are the desired candidates as terahertz source generation. The present work will give contributions to evaluate and search new NLO materials as terahertz source generation