Linear birefringence parameters determination of a multi-order wave plate via phase detection at large oblique incidence angles

In order to characterize the linear birefringence parameters (LBPs) of a multi-order wave plate (MWP) including ordinary refractive index n_o, extraordinary refractive index n_e and the order number precisely, phase retardation measurement by means of large oblique incidence angle on the MWP has been proposed and demonstrated. However, the effects of spatial shifting and multiple reflections by the MWP depress the accuracy of the measurements significantly. Thus, we propose a retro-reflected geometry in a polarized heterodyne interferometer that can determine the LBPs of a MWP precisely. This method is not only able to reduce the spatial shifting effect but also avoids multiple reflections of the emerging beams. Experimentally, the oblique incidence angle in a range from 30° to 44° was scanned and the highest sensitivity ever for measurements of n_o and n_e for an uncoated MWP was obtained. The detection sensitivity for the refractive indices (n_o,n_e, n_o−n_e) of an uncoated MWP can be up to 10⁻⁶.     

Orientational order and distribution function in nematic 1-(4-trans hexylcyclohexyl)-4-[(2-4-isothiocyanato phenyl)ethyl] benzene

The refractive indices (n _e,?n _o) and density have been measured as a function of temperature in the liquid-crystalline and liquid phases of nematic 1-(4-trans hexylcyclohexyl)-4-[(2-4-isothiocyanato phenyl)ethyl] benzene. The molecular polarizability and orientational order parameter have been computed using the Neugebauer anisotropic local field model. The distribution function f(β), and hence the higher order parameter ?P ₄?, and nematic pair-potential have been computed at different temperatures in the nematic phase.     

High spin states in75Se populated by the72Ge(α,n) and73Ge(α, 2n) reaction

The⁷²Ge(α, n)⁷⁵Se and⁷³Ge(α, 2n)⁷⁵Se reactions have been studied at bombarding energies of 15 MeV and 22.5 MeV respectively using Ge(Li)-detectors.γ-singles spectra,γ-γ-coincidences,γ-angular distributions and excitation functions have been taken. A level scheme has been constructed, which contains a stretched spin and a normal rotational band. Nuclear reactions⁷²Ge(α, n)⁷⁵Se,⁷³Ge(α, 2n)⁷⁵Se; measuredE _γ ,I _γ ,γ-γ-coincidences,γ-angular distribution,γ-excitation function.⁷⁵Se deduced levels,J, π, γ-multipolarity. Enriched target, Ge(Li).     

DSC,density and refractive index studies on two nematogenic p-alkylphenyl-2-chloro-4-(p-alkylbenzoyloxy)-benzoates and their mixtures

The compounds p-pentylphenyl-2-chloro-4-(p-pentylbenzoyloxy)-benzoate [PCPB] and p-octylphenyl-2-chloro-4-(p-heptylbenzoyloxy)-benzoate [OCHB], and mixtures of different mole fractions of them, show a nematic phase with a supercooling effect. From DSC studies both ΔH and ΔS at T _NI are found to have minimum values for the equimolar mixture, which happens to be an eutectic mixture (Mix-II). However the density of this mixture is found to be less than that of the pure compounds. Refractive indices (n _o, n_e) are measured by thin prism method at different temperatures for pure components and the eutectic mixture. The birefringence values of the eutectic mixture are less than those of the individual components at higher temperature region, and are in-between at lower temperatures. The principal polarizibilities (α _o, α _e) of all the compounds have been calculated using both Vuks’ and Neugebauer's methods. These values have been compared with those calculated from additivity rules of bond polarizability. The average polarizability α increases with chain length. The orientational order parameter (P ₂) at different temperatures has been calculated using Haller's extrapolation procedure. (P ₂) values of OCHB are found to be greater than those of PCPB and Mix-II at higher temperatures, and are consistent with those determined from our X-ray studies. The temperature dependence of (P ₂) of all the compounds has been compared with Maier-Saupe theoretical values.     

In beam gamma spectroscopy of62Zn

The decay scheme of⁶²Zn has been investigated by studying the yield functions, angular distributions and coincidence relation-ships of theγ-rays emitted in the⁶³Cu(p, 2nγ) and⁶⁰Ni(α, 2nγ) reactions. Spins up to7? were assigned to the observed states. Nuclear Reactions ⁶⁰Ni(α, 2nγ)⁶²Zn,E _α=28–35 MeV and⁶³Cu(p, 2nγ)⁶²Zn,E _p = 22–31 MeV; measuredE _γ,I _γ(θ),I _γ(E _p , andI _γ,E _α-γ coincidences,⁶²Zn deduced decay scheme. Enriched target, Ge(Li) detectors.     

Texture and Optical Studies of the Mesophases of Cyanocyclohexyl Cyclohexanes

Optical studies have been conducted as a function of temperature on two (CCH₃ and CCH₇) of the three odd members of the homologous series of the mesogen trans, trans-4′-alkyl-bicyclohexyl-4-carbonitrite. From birefringence studies the variation of the orientational order parameter ? P₂ ? with temperature of the two members has been determined. Texture studies have been conducted to identify hitherto unidentified phases. A comparative study of the temperature dependence of the refractive indices n _e, n _o , and ? P₂ ? of all the three members CCH₃, CCH₅, CCH₇ have been presented with a view to study the effect of increasing chain length. Comparison of the experimentally obtained ? P₂ ? values has been made with theoretical values predicted by the Maier-Saupe theory.     

Theoretical derivation of a simplified form of the OTOR/GOT differential equation

A simplified form of the OTOR/GOT differential equation has been derived, which may be employed in the evaluation of TL curves for saturated (N = n_o) and non-saturated cases (N > n_o). The present eqn. is found to be theoretically correct and physically sound in comparison with empirical general order kinetics. It has been found that the TL curve evaluated using the present eqn. matches the TL curves evaluated using differential eqn. formalism, and spans the region from α = n_o/(100N) to α = 0.999 (where α is the ratio of the retrapping probability to the recombination probability). The simulated curve resembles a first order kinetics curve when α = n_o/(100N) and a second order kinetics curve when α = 0.999. However, comparison with general order kinetics for the intermediate range is not possible as a one- to-one correspondence between α and b cannot be made. Also, calculation in the saturated case is made simpler since only three unknown parameters (E, s and α) are required.     

On the dynamic conductivity for an electron-impurity system

The correlation function formula for the dynamic conductivity of a system of non-interacting electrons in the field of impurities is analyzed in terms of proper connected diagrams. By selecting those diagrams appropriate in the region of weak coupling and low impurity concentration, a set of coupled equations for the energy broadening γ (ω, ε, n_s) and the energy shift Δ(ω, ε, n_s) is derived, where both γ and Δ depend on the frequency ω of a probing field, the energy ε of the electron, and the concentration, n_g, of impurities. With the assumption of a finite range potential, these equations are solved. It is found that γ (ω, n_s) is smaller than that extrapolated value which the conventional expression γ₀ for the low-concentration collision frequency would predict, in the entire region studied, that the difference γ₀-γ becomes appreciable when the ratio of the average time between scatterings, τ_c, to the average duration of a scattering, τ_d, is 100 or less, that γ (ω, n_s) decreases monotonically from its static value γ (0, n_s), and becomes vanishingly small in the region ω≈1/τ_d, and that in the static limit (ω=0), γ=γ₀[1?(2/π) (γ₀τ_d)+…], that the energy shift Δ is positive, and increases from 0 and reach a peak of magnitude γ₀ as ω is raised from 0. By using the γ and Δ obtained, the dynamic conductivity σ(ω, n_s) for degenerated electrons is calculated. The deviation, σ-σ₀, from the conventional expression σ₀=(?i) (n_ee²/M) [ω-iΓ₀]^?1, (n_e]=number density of electrons), for 0°K, is appreciable when the ratio τ_c/τ_d is 100 or less. The field-term correction, which arises from the modification of the scattering due to the probing field, is found to be negligible in the entire region studied.     

The study of the (n, α) and (n, γ α) reactions on143Nd

Partial cross sections have been measured for the¹⁴³Nd(n _th,α)¹⁴⁰Ce reaction and also for the two-step process¹⁴³Nd(n _th,γα)¹⁴⁰Ce. The results of the present work confirm previous data, but due to lower background, better statistics and resolution improved precision has been obtained. The double-humped structure in the observed (n, γ α) spectrum can still be explained through the Porter-Thomas fluctuations of the reduced partialγ andα widths.     

Negative-parity bands in the 88-neutron nuclei153Tb and155Ho

Bands of negative-parity levels have been observed in in-beam studies of¹⁵³Tb and¹⁵⁵Ho. The data are qualitatively accounted for in the rotation-alignment model as decoupled bands based on the h_11/2 proton orbital. Nuclear Reactions:¹⁵³Eu(α, 4nγ)¹⁵³Tb,E=45–55 MeV;¹⁵⁰Sm(¹⁰B, 5nγ)¹⁵⁵Ho,E=60–70 MeV; measuredE _γ,I _γ (0), γ ? γ coinc.,E _e, I _e ^K ,¹⁵³Tb and¹⁵⁵Ho deduced levels,J, π. Ge(Li) and Si(Li) detectors. Enriched targets.     

High-spin states in112Cd from the110Pd(α, 2n γ)-reaction

The decay scheme of¹¹²Cd has been studied by γ-ray spectroscopy with the¹¹⁰Pd(α, 2nγ) reaction. Spin and parity assignments were made on the basis of coincidence measurements, angular distributions and excitation functions. Twelve new energy levels were established. A vibrational-like positive-parity band up to spin 8⁺ and a negativeparity side band 5^?, (7^?), (9^?) were found. For the negative-parity states a (v_j, vh_11/2) configuration is suggested. Nuclear Reactions:¹¹⁰Pd(α,2nγ),E _α =15–22.5 MeV; measuredE _γ ,E _γ , (E,E _γ ),E _γ (θ),γ-γ- coincidence;¹¹²Cd deduced levels,J; enriched target.     

Reinvestigation of the decay scheme of the short-lived isomeric states in112In

The two short-lived isomeric states in¹¹²In have been reinvestigated by means of the¹¹²Cd(d, 2n) and¹⁰⁹Ag (α, n) reactions. Measurements of delayed X- andγ-ray, lifetime and TDPAD spectra have been performed. A 6.32(3) keVγ-ray has been identified in the isomeric decay and anM1 multipolarity has been assigned to it on the basis of the measured internal conversion coefficients:α _L =196(39) andα _tot=231(35). TheE1+M2(δ =+0.24(4)) andE2 multipolarities have been determined for the 263 and 188 keV transitions deexciting the 8^?(T _1/2=2.82(2) μs) and 7⁺ (T _1/2=0.93(2) μs) isomeric states, respectively. A revised isomeric decay scheme is presented.     

The Stückelberg holographic superconductors with Weyl corrections

In this Letter we construct the Stückelberg holographic superconductor with Weyl corrections. Under such corrections, the Weyl coupling parameter γ plays an important role in the order of phase transitions and the critical exponents of second order phase transitions. So do the model parameters cα, α and c₄. Moreover, we show that the Weyl coupling parameter γ and the model parameters cα, α, c₄ which together control the size and strength of the conductivity coherence peak and the ratio of gap frequency over critical temperature ωg/Tc.     

Threshold and spin factors in the yield of bremsstrahlung-induced reactions

Relative yields of photon-induced reactions are systematized in a function of the threshold parameter for moderately heavy targets at the bremsstrahlung end-point energy lower than 30 MeV. Regular dependence is established for the group of (γ, n), (γ, p), and (γ, d) reactions, while the yields of (γ, 2n) and (γ,α) reactions deviate from the regularity. Physical conclusions are discussed and possible application of this systematic for data processing is proposed. In particular, the constituent threshold and spin factors in the isomer-to-ground-state ratio could be isolated separately. For spin dependence of the yields, a new regularization parameter is introduced and previously hidden peculiarities are concluded.     

Thermo-optical properties of uniaxial NaT(XO4)2 laser host crystals (where T = Y, La, Gd or Bi, and X = W or Mo)

Thermo-optic coefficients dn _o/dT and dn _e/dT were measured in tetragonal double tungstate and double molybdate crystals NaT(XO₄)₂ (where T = Y, La, Gd or Bi and X = W or Mo) by a laser beam deviation method in the spectral range 0.4–1.1 μm. Thermal expansion coefficients in the directions of a and c crystallographic axes were also measured. Analytical expressions for thermo-optic dispersion formulas were derived as series in 1/λ ². All dn/dT values for NaT(XO₄)₂ crystals were found to be negative. Their absolute values satisfy the relation |dn _e/dT| > |dn _o/dT| for crystals without Bi and |dn _o/dT| > |dn _e/dT| for crystals with Bi. A clear tendency for dn/dT values to decrease with the increase of the volumetric thermal expansion coefficient α _vol of the crystal was observed. This is related with dominant contribution of volumetric thermal expansion effect to the temperature dependence of the refractive index. Thermal coefficients of the optical path W = dn/dT + (n ? 1)α _T governing thermal lensing effect were calculated for different light propagation directions and polarizations as well as crystal athermal directions.     

Crystallization kinetics of a-Ga5Se95−xSbx

The kinetics studies of a-Ga₅Se_95−xSb_x (x=0, 1, 5, 10) is analyzed by an isothermal and non-isothermal technique. By isothermal technique the analysis of crystallization kinetics is taken at temperatures between the glass transition and crystallization. The activation energy of crystallization (ΔE_c) and order parameter (n) are calculated by fitting the values of extent of crystallization (α) in the Avrami's equation. By non-isothermal technique crystallization kinetics of a-Ga₅Se_95−xSb_x (x=0, 1, 5, 10) with different heating rates of 5, 10, 15 and 20 K/min have been studied by using the Differential Scanning Calorimeter (D.S.C.). The glass transition temperature, crystallization temperature at different heating rates and structural change during glass transition has been determined from an empirical relation. From the heating rate, the dependence of the glass transition and crystallization temperatures, the activation energy for structural relation (Δe_t), the activation energy of crystallization (ΔE_c), and the order parameter (n) are calculated.     

Properties of exchange interaction in Yb3Fe5O12 under extreme conditions

In Yb₃Fe₅O₁₂, the exchange effective field can be expressed as H_eff=−λ·M_Fe=−λχ_eff·H_e=−γ·H_e where γ is named as the exchange field parameter and H_e is the external magnetic field. Then, in this paper, by the discussions on the characteristics of the exchange field parameter γ, the properties of exchange interaction in ytterbium iron garnet (Yb₃Fe₅O₁₂) are analyzed under extreme conditions (high magnetic fields and low temperatures). Our theory suggests that the exchange field parameter γ is the function of the temperatures under different external magnetic fields, and γ=a+b·T+c·T², where the coefficients a, b, c are associated with the external magnetic fields and the magnetized directions. Thus, the temperature-dependence, field-dependence and anisotropic characteristics of the exchange interaction in Yb₃Fe₅O₁₂ are revealed. Also, excellent fits to the available experiments are obtained.     

Optical characterization of nano-structured Cu2ZnSnS4 thin films deposited by GLAD technique

In this paper, Cu₂ZnSnS₄ (CZTS) thin films were elaborated at room temperature by thermal evaporation method using Glancing Angle Deposition (GLAD) technique at different incident angles γ = 00°, 20°, 40°, 60°, 75° and 85°. XRD, Raman scattering analysis, (SEM) and UV-Visible-NIR spectroscopy were used to characterize the crystalline structure, morphology and optical properties of CZTS samples. The results have showed that the ellipsometric analysis leaded to an optical anisotropy due to the structural anisotropy for CZTS samples deposited at γ = 85°. All Cu₂ZnSnS₄ samples exhibited a high absorption coefficient (α > 10⁴ cm⁻¹) and a direct optical transition varied between 1.48 eV and 2.05 eV for CZTS thin films deposited at γ = 00° and 85°, respectively. The value of the Urbach energy increased with incident angle, indeed, its value increased from 58 meV (γ = 00°) to 604 meV (γ = 75°) and decrease to be 368 meV for γ = 85°. This result is correlated with the Raman analysis. From transmittance data of CZTS thin films deposited at γ = 00°, 20° and 40° Swanepoel's method was used, to estimate the refractive index n. It allows us, using the Wemple-DiDomenico and Spitzer-Fan models, to calculate other optical parameters such as the oscillator energy E₀, dispersion energy E_d, zero frequency refractive index n₀, high frequency dielectric constant ε_∞ and the electric susceptibility χ_e. On the other hand, to have an idea about the evolution of the nonlinear optical character, the nonlinear susceptibility χ⁽³⁾ and the nonlinear refractive index n₂ of CZTS thin films deposited at γ = 00°, 20° and 40° were investigated. Ellipsometric measurements of CZTS thin films has leaded to an optical anisotropy for γ = 85°. In addition, the generalized ellipsometry in Jones formalism have proved this property, which can be related to the nano-columnar slanted structure as revealed by (SEM) analysis.     

High spin states in73Se observed by the reaction70Ge(α,nγ)

⁷³Se has been investigated by the reaction⁷⁰Ge(α, nγ). Gamma excitation functions (E _α=10–16 MeV), gamma angular distributions (E _α=18 MeV) and gamma-gamma coincidences (E _α=15 MeV)) have been taken. A level scheme has been established, spins and partities have been assigned. States of a rotational band on the 151.2 keV (5/2^?) state and an anomalous band have been identified. Nuclear Reaction⁷⁰Ge(α,nγ)E _α=15 and 18 MeV; measuredE _γ,I _γ,γ-γ-coin.,γ-angular distribution,γ-excitation function.⁷³Se deduced levels,J, π. Enriched target, Ge(Li).     

Explicit solution for the optical properties of a uniaxial crystal in generalized ellipsometry

The complex ordinary (N_o) and extraordinary (N_e) refractive indices of an absorbing uniaxial crystal can be explicitly derived from the normalized diagonal (α) and off-diago-nal (β) elements of one oblique-incidence (at angle φ) reflection matrix measured by generalized ellipsometry on a crystal face that contains the optic axis at an oblique orientation (ω ≠ O or $\text{π}\text{2}$) with respect to the plane of incidence. At most four solution sets (N_o, N_e) are mathematically and physically consistent with one measurement set (α,β,φ,ω). In many cases, identification of the correct solution is feasible without additional measurements. If necessary repeated measurements at a different value of φ or ω will resolve the ambiguity; only one solution set remains invariant upon a change of φ or ω, the correct set. A single measurement of reflectance (e.g., for p-polarized light) may also be adequate. The analytic inversion method is used in an error analysis to determine optimum choices of angle of incidence (φ ? 50–70°) and crystal orientation (ω ? 45°) that lead to minimum percentage errors of N_o and N_e for several uniaxial crystals.