Investigation of the Linear and Nonlinear Optical Susceptibilities of KTiOPO₄ Single Crystals: Theory and Experiment

Abstract

Experimental and theoretical studies of the linear and nonlinear optical susceptibilities for single crystals of potassium titanyl phosphate KTiOPO₄ are reported. The state-of-the-art full potential linear augmented plane wave method, based on the density functional theory, was applied for the theoretical investigation. The calculated direct energy band gap at Γ, using the Engel-Vosko exchange correlation functional, is found to be 3.1 eV. This is in excellent agreement with the band gap obtained from the experimental optical absorption spectra (3.2 eV). We have calculated the complex dielectric susceptibility ε(ω)dispersion, its zero-frequency limit ε₁(0) and the birefringence of KTiOPO₄. The calculated birefringence at the zero-frequency limit Δn(0) is equal to about 0.07 and Δn(ω) at 1.165 eV (λ = 1064 nm) is 0.074. We also report calculations of the complex second-order optical susceptibility dispersions for the principal tensor components: χ₁₁₃((2))(ω), χ₂₃₂((2))(ω), χ₃₁₁((2))(ω), χ₃₂₂((2))(ω), and χ₃₃₃((2))(ω). The intra- and interband contributions to these susceptibilities are evaluated. The calculated total second order susceptibility tensor components |χ(ijk)((2))(ω)| at λ = 1064 nm for all the five tensor components are compared with those obtained from our measurements performed by nanosecond Nd:YAG laser at the fundamental wavelength (λ = 1064 nm). Our calculations show reasonably good agreement with our experimental nonlinear optical data and the results obtained by other authors. The calculated the microscopic second order hyperpolarizability, β₃₃₃, vector component along the dipole moment direction for the dominant component χ₃₃₃((2))(ω) is found to be 31.6 × 10⁻³⁰ esu, at λ = 1064 nm.

FP-LAPW investigation of mechanical and thermodynamic properties of Na2X (X = S and Se) under pressure and temperature effects

“…This method has proven to be one of the most accurate methods for the computation of the electronic structure of solids within DFT [40][41][42][43][44][45]. In this scheme of calculations APW+lo basis set is incorporated to represent the electronic band structure for all atoms as well as corresponding orbitals.…”

Structural Reasons for the Nonlinear Optical Properties of KTP Family Single Crystals

“…Recent publications with ab initio computations for the electronic structure and nonlinear optical characteristics of KTP-type crystals [30][31][32] emphasized the distortion of TiO 6 octahedra, originating the superior nonlinear optical properties of these crystals. The distorted octahedron allows the dipolar excited states to mix with the bonding electronic states producing a strong hyperpolarizability on the Ti-O bonds [30].…”

“…The distorted octahedron allows the dipolar excited states to mix with the bonding electronic states producing a strong hyperpolarizability on the Ti-O bonds [30]. In [31], it was found that the band structure of KTP-type phosphate crystals was dominated by Ti and O states and weakly dependent on the nature of the alkali-site element.…”

Dispersion of the linear and nonlinear optical susceptibilities of the CuAl(S1−xSex)2 mixed chaclcopyrite compounds

“…19 The specific A XI B XIII C XVI 2 chalcopyrites concerned in this work used copper as the group XI element, aluminum as the group XIII element, and sulfur or selenium as the group XVI element (the standard group numbering of the chemical elements in the periodic table is used, as recommended by the International Union of Pure and Applied Chemistry (IUPAC)). Since these compounds display large birefringence, [25][26][27][28] they are potentially interesting as nonlinear optical materials, as well as semiconductors, whose band gap favors their applications for solar energetic. So far, however, the trends of the coupling coefficients in these materials are a)…”