Electronic structure, linear, nonlinear optical susceptibilities and birefringence of CuInX2 (X = S, Se, Te) chalcopyrite-structure compounds

The electronic structure, linear and nonlinear optical properties have been calculated for CuInX2 (X=S, Se, Te) chalcopyrite-structure single crystals using the state-of-the-art full potential linear augmented plane wave (FP-LAPW) method. We present results for band structure, density of states, and imaginary part of the frequency-dependent linear and nonlinear optical susceptibilities. We find that these crystals are semiconductors with direct band gaps. We have calculated the birefringence of these crystals. The birefringence is negative for CuInS2 and CuInSe2 while it is positive for CuInTe2 in agreement with the experimental data. Calculations are reported for the frequency-dependent complex second-order non-linear optical susceptibilities . The intra-band and inter-band contributions to the second harmonic generation increase when we replace S by Se and decrease when we replace Se by Te. We find that smaller energy band gap compounds have larger values of in agreement with the experimental data and previous theoretical calculations.Comment: 17 pages, 6 figure

First-principle calculations of the linear and nonlinear optical response for GaX (X=As, Sb, P)

The linear and nonlinear optical properties in non-centro-symmetric cubic semiconductor GaX (X=As, Sb, P) are studied by using the first-principle full potential linear augmented plane wave (FP-LAPW) and the linear muffin-tin orbital (LMTO) methods. We present calculations of the frequency-dependent complex dielectric function $\varepsilon \left( \omega \right)$ and it zero-frequency limit $\varepsilon _1 \left( 0 \right)$ . A simple scissor operator is applied to adjust the band gap from the local-density calculations to match the experimental value. Calculations are reported for the frequency-dependent complex second-order non-linear optical susceptibilities $\chi ^2\left( \omega \right)$ up to 6 eV and it zero-frequency limit $\chi ^2\left( 0 \right)$ . Comparison with available experimental data shows good agreement. Our calculations show excellent agreement between the two methods. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005

Reduction of the pulse duration of the ultrafast laser pulses of the Two-Photon Laser Scanning Microscopy (2PLSM)

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background: We provide an update of our two-photon laser scanning microscope by compressing or reducing the broadening of the pulse width of ultrafast laser pulses for dispersion precompensation, to enable the pulses to penetrate deeply inside the sample. Findings: The broadening comes as the pulses pass through the optical elements. We enhanced and modified the quality and the sharpness of images by enhancing the resolution using special polarizer namely Glan Laser polarizer GL10. This polarizer consists of two prisms separated by air space. This air separation between the two prisms uses to delay the red wavelength when the light leaves the first prism to the air then to second prism. We note a considerable enhancing with using the GL polarizer, and we can see the details of the leaf structure in early stages when we trying to get focus through z-stacks of images in comparison to exactly the same measurements without using GL polarizer. Hence, with this modification we able to reduce the time of exposure the sample to the laser radiation thereby we will reduce the probability of photobleaching and phototoxicity. When the pulse width reduced, the average power of the laser pulses maintained a

Electronic structure and magneto-optic Kerr effect in ferromagnetic titanium oxyphosphates Li0.50Co0.25TiO(PO4): An ab-initio study

The X-ray diffraction for Li0.50Co0.25TiO(PO4), was used as a starting point to perform structural optimization by minimizing the forces acting on the atoms. We have performed a comprehensive theoretical study of electronic properties, including magneto-optic Kerr effect, of titanium oxyphosphates Li0.50Co0.25TiO(PO4) in the ferromagnetic phase. The generalized gradient approximation (GGA) exchange-correlation potential was applied within the full potential linear augmented plane wave (FP-LAPW) method. The total energy of the ferromagnetic state is 0.72 eV less than that of the paramagnetic state. The total moment is found to be 2.99 mu(B) with a major contribution of 2.47 mu(B) coming from the Co atoms. In addition, we have calculated the total and partial densities of states. The electron charge densities and the bonding properties are analyzed and discussed. As a remarkable finding we note that the ferromagnetic Li0.50Co0.25TiO(PO4), is semiconducting with energy gap of about 1.2 eV for the minority spin and as semi-metallic for the majority spin, in contrast to the paramagnetic Li0.50Co0.25TiO(PO4) which shows metallic behavior. From the calculated results of band structure and density of states, the half-metallic character and stability of ferromagnetic state for Li0.50Co0.25TiO(PO4) is determined. The bonding properties of the ferromagnatic Li0.50Co0.25TiO(PO4) have been analyzed through the electronic spin charge density contours in the (1 0 0) and (1 1 0) planes. The Kerr rotation spectrum is controlled by sigma(xy)(2) (omega) at low energies (1.5-3.0 eV) because sigma(xx)(1) (omega) is almost constant. The value of the Kerr rotation is close to 0.1 degree at low energies

Bismuth-containing semiconductors: Linear and nonlinear optical susceptibilities of GaAs1−x Bix alloys

Using all electron full potential – linearized augmented plane wave (FP-LAPW) method the linear and nonlinear optical susceptibilities of cubic GaAs1−xBix alloys with x varying between 0.25 and 0.75 with increment of 0.25 are investigated. We have applied the generalized gradient approximation (GGA) for the exchange and correlation potential. In addition the Engel–Vosko generalized gradient approximation (EVGGA) was used. The reflectivity, refractivity, absorption coefficient and the loss function of these ternary alloys were investigated. The absorption coefficient shows that GaAs0.25Bi0.75 possess the highest coefficient among the investigated alloys which supports our previous observation that the band gap decreases substantially with increasing Bi content and the materials with very small energy band gap possess the highest absorption coefficient. The investigation of the linear and nonlinear optical susceptibilities of GaAs1−xBix shows a strong band gap reduction as commonly found experimentally

Phase transition in BaThO3 from Pbnm to Ibmm turn the fundamental energy band gap from indirect to direct

The influence of phase transition on the electronic structure and the optical properties of BaThO3 is investigated by means of density functional theory. At room temperature BaThO3 is stable in the Pbnm phase, whereas it is stable in the Ibmm phase at high temperature. The transition from the Pbnm to the Ibmm phase cause a change in the band gap (Eg) nature from indirect to direct and a reduction by around 0.3 eV. The calculated Eg is about 4.9 eV (Pbnm) and 4.6 eV (Ibmm). The phase transition influences the k-dispersion of bands around the Fermi level and, hence, the effective masses resulting in increasing the mobility of the charge carrier and enhancing the charge transfer mechanism. The obtained optical properties clearly show the influence of phase transition on the electronic structure. It was noticed that moving from Pbnm →Ibmm phase leads to shift the whole spectral structure towards lower energies by around 0.3 eV and increase the magnitudes of the optical components. It is found that the Pbnm and Ibmm phases exhibit negative uniaxial anisotropy and negative birefringence

Density Functional Calculations, Electronic Structure, and Optical Properties of Molybdenum Bimetallic Nitrides Pt2Mo3N and Pd2Mo3N

The electronic band structure, origin of chemical bonds, and dispersion of linear optical susceptibilities for Pt2Mo3N and Pd2Mo3N have been investigated within the framework of density functional theory (DFT). The atomic positions of Pt2Mo3N and Pd2Mo3N crystalline compounds taken from the X-ray diffraction data (El-Himri, A.; Marrero-Lopez, D.; Nunez, P. J. Solid State Chem.2004, 177, 3219) were optimized by minimization of the forces acting on the atoms using a full potential linear augmented plane wave (FLAPW) method. We employed the generalized gradient approximation (GGA) of Perdew, Burke, and Ernzerhof (PBE). The DFT calculations show that these compounds have metallic origin with strong orbital hybridization near the Fermi energy level (EF). The calculated density of states (DOS) at the Fermi energy (EF) is about 1.83 and 1.02 states/Ry cell, and the bare linear low-temperature electronic specific heat coefficient (γ) is found to be 0.32 and 0.18 mJ/mol-K2 for Pt2Mo3N and Pd2Mo3N, respectively. The Fermi surface of Pt2Mo3N (Pd2Mo3N) is composed of three (five) sheets. The bonding features of the compounds are analyzed using the electronic charge density contour in the (110) crystallographic plane. The linear optical properties are calculated with and without the Drude term

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

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 |χijk(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

Linear and nonlinear optical susceptibilities and hyperpolarizability of borate LiNaB4O7 single crystals: Theory and experiment

LiNaB4O7 was synthesized by employing high-temperature reaction methods. The purity of the sample was checked by x-ray powder diffraction. The optical properties were measured by analyzing the diffuse reflectance data which showed a band gap of about 3.88 eV. Linear and nonlinear optical susceptibility calculations have been performed using the all-electron full potential linearized augmented plane wave method using four different exchange correlation potentials. It was found that the title compound possesses an optical gap of about 2.80 eV using the local density approximation, 2.91 eV by generalized gradient approximation, 3.21 eV for the Engel-Vosko generalized gradient approximation (EVGGA), and 3.81 eV using modified Becke-Johnson potential (mBJ). This compares well with our experimentally measured energy band gap of 3.88 eV. Our calculations show that EVGGA and mBJ cause a blue spectral shift with significant changes in the whole spectra. The observed spectral shifts are in agreement with the calculated band structure and corresponding electron density of states. The tensor chi((2))(ijk) describes the second-order nonlinear optical effect and the symmetry allows only five nonzero components, namely, the 113, 232, 311, 322, and 333 components with 322 being the dominant one with a value 0.15 pm/V (d(32) = 0.0733 pm/V) at static limit and 0.16 pm/V (d(32) = 0.0795 pm/V) at lambda = 1064 nm. For the dominant component, the microscopic second order hyperpolarizability, beta(322), was found to be 0.306 x 10(-30) esu at static limit and 0.332 x 10(- 30) esu at lambda = 1064 nm. (C) 2012 American Institute of Physics