Measurement of the optical transmission modes and losses of the poled guest–host polymer NAEC/PEK-c planar waveguides

The polyetherketone (PEK-c) guest–host polymer planar waveguides doped with (4′-nitro)-3-azo-9-ethyl-carbazole (NAEC) were prepared. The waveguide films were poled by corona-onset poling at elevated temperature (COPET), and the corona poling setup includes a grid voltage making the surface-charge distribution uniform. By using the prism-in coupling method, the dark-line spectrum given by the reflected intensity versus the angle of incidence have been obtained, and the optical transmission losses of mth modes have been measured for the poled polymer waveguides at λ=632.8 nm. The measurement result showed that the optical loss of the fundamental mode is less than 0.7 dB cm⁻¹ for the TE polarization.     

Photoinduced non-linear optical diagnostic of SiNxOy/Si111 interfaces

Anisotropic (elliptically polarized) photoinduced second harmonic generation (PISHG) in SiN_xO_y/Si1 1 1 films was proposed for contact-less monitoring of specimens with different nitrogen to oxygen (N/O) ratios. As a source for the photoinducing light, we used a nitrogen Q-switched pulse laser at wavelengths of 315, 337 and 354 nm as well as doubled frequency YAG–Nd laser wavelength (λ=530 nm). The YAG : Nd pulse laser (λ=1.06 μm; W=30 MW; τ=10–50 ps) was used to measure the PISHG. All measurements were done in a reflected light regime. We found that the output PISHG signal was sensitive to the N/O ratio and the film thickness. Measurements of the PISHG versus pumping wavelengths, powers, incident angles as well as independent measurements of the DC-electric field induced second harmonic generation indicate the major role played in this process by axially symmetric photoexcited electron–phonon states. The SiN_xO_y films were synthesized using a technique of chemical evaporation at low pressures. Films with thickness varying between 10 and 30 nm and with an N/O ratio between 0 and 1 were obtained. Electrostatic potential distribution at the Si1 1 1–SiN_xO_y interfaces was calculated. Comparison of the experimentally obtained and quantum chemically calculated PISHG data are presented. High sensitivity of anisotropic PISHG to the N/O ratio and film thickness is revealed. The role of the electron–phonon interactions in the dependencies observed is discussed. We have shown that the PISHG method has higher sensitivity than the traditional extended X-ray absorption fine structure spectroscopic and linear optical method for films with the N/O ratio higher than 0.50.     

Optical Properties of Films of Cu x Ag1−x InSe2 Solid Solutions Obtained by Laser Evaporation

The structure and optical properties of the films of ternary compounds AgInSe₂, CuInSe₂ and Cu _x Ag_1–x InSe₂ solid solutions obtained by pulsed laser evaporation are investigated. It has been established that the films like bulk crystals have the structure of chalcopyrite. By the transmission and reflection spectra near the edge of natural absorption the refractive index and coefficient of optical absorption are calculated and the energies of interband transitions and the crystalline and spinorbit splitting are determined.     

Optical properties of AsSe1.5−xTex glassy system

Thin AsSe_1.5−xTe_x films with 0x<1.5 have been prepared by a thermal vacuum evaporation technique onto quartz and glass substrates kept at room temperature (300 K). The optical constants, the refractive index, n, and the absorption index, k, of the films were determined for the investigated compositions of different thickness values (100–300 nm) using spectrophotometric measurements of the transmittance, T, and the reflectance, R, at normal incidence in the spectral range 400–2500 nm. The obtained values of both n and k were found to be independent of the film thickness within the above mentioned thickness range. The estimated indirect and direct optical energy gap decreased as tellurium content increased in the parent sample AsSe_1.5. The values of dispersion energy, E_d, and lattice dielectric constant, _L, of the system have been determined and correlated with the type and amount of chemical bonds and the relative proportion of the constituent elements in the examined compositions.     

Dispersive optical constants of glassy AsSe1−xTex system

The compositional dependence of the optical constants, the refractive index n, and the absorption index k, of the AsSe_1−xTe_x thin films with 0<x<1.0 were determined in the spectral range of 400–2500 nm. The maximum value of the refractive index n, is shifted toward the long wavelength by increasing the Te content in the examined system. The values of the forbidden energy gap of the system have been determined and were correlated with the type and the amount of chemical bonds formed by the increasing Te content in the AsSe_1−xTe_x glassy system. The value of the dispersion energy E_d exhibits low value at the composition containing the same atomic percent of Se and Te.     

Dispersive optical constants of a-Se100−xSbx films

Thin films of amorphous Se_100−xSb_x (x=5,10 and 20 at%) system are deposited on a silicon substrate at room temperature (300 K) by thermal evaporation technique. The optical constant such as refractive index (n) has been determined by a method based on the envelope curves of the optical transmission spectrum at normal incidence by a Swanpoel method. The oscillator energy (E_o), dispersion energy (E_d) and other parameters have been determined by the Wemple–DiDomenico method. The absorption coefficient (α) has been determined from the reflectivity and transmitivity spectrum in the range 300–2500 nm. The optical-absorption data indicate that the absorption mechanism is a non-direct transition. We found that the optical band gap, E_g^opt, decreases from 1.66±0.01 to 1.35±0.01 eV with increase Sb content.     

Structural and optical studies of thermally evaporated CoPc thin films

The structure of the thermally evaporated cobalt phthalocyanine (CoPc) thin film in the β-form is investigated, and shows a single strong peak indicating preferential orientation in the (1 0 0) direction. Some structural parameters such as crystallite grain size, dislocation density and the number of crystallites per unit surface area are determined.The spectral parameters are determined by applying the electronic orbital transitions.But the optical parameters are deduced using band-model consideration for thin films of Pc.The spectral and optical parameters have also been investigated by using the spectrophotometric measurements of transmittance and reflectance in the wavelength range 200–2500 nm.The absorption spectra recorded in the UV–VIS region show two absorption bands of phthalocyanine (Pc) molecule, namely the Soret band (B) and the Q-band. The Q-band shows its characteristic splitting (Davydov splitting) with ΔQ=0.23 eV.Some of the important spectral parameters, namely optical absorption coefficient (α), molar extinction coefficient (_molar), oscillator strength (f), electric dipole strength (q²) and absorption half bandwidth (Δλ) of the principle optical transitions have been evaluated.The fundamental and the onset indirect energy gaps could be estimated as 2.90 + or − 0.05 and 1.51 eV, respectively.The refractive index showed an anomalous dispersion in the absorption region as well as normal dispersion in the transparent region. From analysis of dispersion curves, the dielectric constants, the dispersion parameters and the molar polarizability were obtained.All the above parameters were obtained for films as deposited and as annealed. No remarkable annealing effect on many parameters was observed.     

Far-infrared dielectric functions and phonon spectra of alloys determined by spectroscopic ellipsometry

We have used spectroscopic ellipsometry to determine the complex dielectric function of a series of ternary Be_xZn_1−xTe thin films grown by molecular beam epitaxy. The II–VI semiconductor alloys were grown on InP substrates that had an InGaAs buffer layer. After the growth, X-ray diffraction experiments were performed in order to determine the alloy concentration. A standard inversion technique was used to obtain the dielectric functions from the measured ellipsometric spectra, obtained between 2000 nm (5000 cm⁻¹) and 40,000 nm (250 cm⁻¹). By modelling the dielectric function as a collection of oscillators, representing longitudinal and transverse optical phonons of the Be_xZn_1−xTe lattice, we were able to recover the phonon spectra for this alloy system. It is argued that the additional phonon modes that are obtained from ellipsometry are best understood from the recently-proposed percolation model.     

Investigation of the linear electro-optic effect for the guest–host polymer DR13/PEK-c thin films

The polyetherketone (PEK-c) guest–host polymer thin films doped with disperse red 13 were prepared by spin-coating method. The corona poling condition was optimized by the poling profiles. The polymer films were poled by corona-onset poling at elevated temperature, and the corona poling setup includes a grid voltage making the surface-charge distribution uniform. The linear electro-optic coefficients of the poled polymer films have been determined at λ=632.8 nm by using a new simple interferometric technique, which is based on compensating the change of the optical length due to the electro-optic effect of the poled polymer film by the anti-piezoelectric effect of a quartz crystal.     

The experimental and theoretical investigation of vibration spectra in ferroelectric semiconductor SbSBrxI1−x crystals

The vapor grown SbSBr_xI_1−x (x=0.1; 0.5; 0.9) crystals with clear mirror surfaces have been used for infrared reflection measurements with Fourier spectrometer. The vibration frequencies along c(z)-axis have been derived from Kramers–Kroning and optical parameters fitting analysis of the experimental reflectivity spectra at T=300 K. The theoretical vibration spectra of SbSBr_xS_1−x (x=0.1; 0.5; 0.9) crystals in paraelectric phase (T=300 K) along c(z)-axis have been determined in quasiharmonic approximation by diagonalization of dynamical matrix. The theoretical vibration spectra of these crystals in a–b(x−y) plane have been determined in harmonic approximation. In this work we discuss the nature of anharmonism in SbSBr_xI_1−x crystals along the c(z)-axis.     

Effect of gamma irradiation on the optical properties of nano-crystalline InP thin films

Thin films of InP were prepared onto glass and quartz substrates using laser ablation technique. Some of the prepared films were irradiated using a ⁶⁰Co γ -ray source irradiation with a total dose of 100 kGy at room temperature. The as deposited and irradiated films were identified by scanning electron microscopy, SEM and X-ray diffraction, XRD. The SEM images have shown a nano-flower like structure for the as deposited films and influenced by the irradiation dose. The Optical characterizations of the as deposited and irradiated InP films were studied using spectrophotometric measurements of transmittance T(λ) and reflectance, R(λ) at normal incidence of light in the spectral range from 200 nm to 2500 nm. The refractive index, n, and the absorption index, k values were calculated using a modified computer program based on minimizing (ΔT)² and (ΔR)² simultaneously, within the desired accuracy. Analysis of the dispersion of the refractive index in the range 900 ≤ λ ≤ 2500 was discussed in terms of the single oscillator model. The optical parameters, such as the dispersion energy, E_d, the oscillator energy, E_o, the high frequency dielectric constant, _∞ and the lattice dielectric constant, _L were evaluated for the as deposited and irradiated films. The allowed optical transitions were found to be direct for the as deposited and irradiated films with energy gaps of 1.35 eV and 1.54 eV, respectively.     

Macroscopic and microscopic parameters of laser dye solvents: m-xylene and dioxane

For the laser designer and other users the optical, electrical and refractive parameters have been obtained for pure nonpolar laser dye solvents m-xylene and dioxane. The refractive index (n) and its thermo-optic constant (dn/dT) at argon laser wavelength 514.5 nm and He–Ne laser wavelength 632.8 nm, are measured. The values of n and dn/dT are used to calculate the optical permittivity ε=n² and its variation with temperature dε/dT. Applying Cauchy's equation the optical and dielectric dispersion (dn/dλ and dε/dλ) are determined. The variation of −dn/dT, −dε/dT, molar refractivity and thermal volume expansion coefficient as a function of wavelength are calculated and represented. Furthermore Cauchy's constants A and B as a function of temperature are plotted. The specific and molar refractivities, specific and molar dispersivity total polarizability, distortion polarizability, ratio of atomic to electronic polarizability, molecular radius, relaxation time, electric susceptibility characteristic impedance, and other physical parameters were calculated. Additionally, density, thermal linear expansion coefficient and molar polarization as a function of temperature were calculated at the laser wavelengths 514.5 nm.     

Structural and optical properties of thermally evaporated thin films

Chalcogenide glass Se₅₅Ge₃₀As₁₅ have amorphous structure in both as-deposited and annealed conditions. The optical properties of the as-deposited and annealed films were studied using spectrophotometric measurements of transmittance, T(λ), and reflectance, R(λ), at normal incidence of light in the wavelength range 200–2500 nm. Neither annealing temperature nor film thickness can influence spectral response on refractive index and absorption index of films. The type of electronic transition responsible for optical properties is indirectly allowed transition with energy gap of 1.94 eV and phonon energy of 40 meV. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple–Didomenico (WD) model. The width of band tails of localized states into the gap (ΔE), the single oscillator energy (E_o), the dispersion energy (E_d), the optical dielectric constant (ε_∞), the lattice dielectric constant (ε_L), the plasma frequency (ω_p) and the free charge carrier concentration (N) were estimated.     

Holographic cure monitoring of the DuPont Somos 7100 stereolithography resin

The optical characteristics of a commercial UV curable resin are investigated using non-degenerate four-wave mixing. The material assessed is an epoxy resin, DuPont Somos^TM 7100. The holographic gratings were written at a wavelength of λ=351.1 nm for an irradiance range 0.5–3.0 W/cm² and read at λ=632.8 nm in order to assess the reactivity, curing speed, shrinkage and resolution of the resin.     

Laser-induced changes on optical band gap of amorphous and crystallized thin films of Se75S25−xAGx

Optical band gap of amorphous, crystallized, laser induced amorphous and laser induced crystallized films of Se₇₅S_25−xAg_x (x=4, 6 and 8) glassy alloys was studied from absorption spectra. The amorphous and crystallized films were induced by pulse laser for 10 min. After laser irradiation on amorphous and crystalline films, optical band gap was measured. It has been found that the mechanism of the optical absorption follows the rule of indirect transition. The amorphous thin films show an increase in the optical band gap, while the crystallized (thermally annealed) thin films show a decrease in the optical band gap by inducing laser irradiation. Crystallization and amorphization of chalcogenide films were accompanied with the change in the optical band gap. The change in optical energy gap could be determined by identification of the transformed phase. These results are interpreted in terms of concentration of localized states due to shift in Fermi level.     

Growth, structural and optical properties of CdxZn1−xS thin films deposited using spray pyrolysis technique

Cd_xZn_(1−x)S (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) thin films were deposited by the chemical spray pyrolysis technique using a less used combination of chemicals. Depositions were done at 573 K on cleaned glass substrates. The composition, surface morphology and structural properties of deposited films were studied using EDAX, SEM and X-ray diffraction technique. XRD studies reveal that all the films are crystalline with hexagonal (wurtzite) structure and inclusion of Cd into the structure of ZnS improved the crystallinity of the films. The value of lattice constant ‘a’ and ‘c’ have been observed to vary with composition from 0.382 to 0.415 nm and 0.625 to 0.675 nm, respectively. The band gap of the thin films varied from 3.32 to 2.41 eV as composition varied from x = 0.0–1.0. It was observed that presence of small amount of cadmium results in marked changes in the optical band gap of ZnS.     

Effect of In-content on the optical properties of a-Se films

The optical transmission spectra of amorphous (a-) Se_1−xIn_x films, with x = 0.0, 0.05, 0.18 and 0.35, that prepared by thermal evaporation from their corresponding bulk ingots, are recorded over the spectral region of 500–2500 nm. A simple straight forward procedure proposed by Swanepeol has been applied to determine the two components of the complex refractive index (). The dispersion of is examined in terms of the Wemple and DiDomenico model and is discussed in terms of In-content. An estimation of various optical parameters such as, the optical energy gap (E_g = 1.96–1.33 eV), single oscillator energy (E_o = 3.95–3.16 eV), oscillator dispersion energy (E_d = 22.6–31.6 eV), lattice oscillator strength (E_l = 0.38–0.61 eV) and wavelength at zero material dispersion (λ_c = 2.0569–2.0879 μm) have been given and discussed in relation to the coordination number, hydrostatic density and formed chemical bonds that are introduced in the network of a-Se with the introduction of up to 35 at.% In.     

Physical,optical and electrical properties of calcium bismuth borate glasses

The variation in physical, optical and electrical properties has been investigated as a function of Bi₂O₃ content in 20CaO?·?xBi₂O₃?·?(80???x)B₂O₃ (0?≤?x?≤?60, in mol%) glasses. The samples were prepared by normal melt-quenching process, and the optical absorption and reflection spectra were recorded in the wavelength range of 400–950 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The optical band gap, E _g, for indirect allowed and indirect forbidden transitions has been determined from the available theories and its value lies between 1.80–2.37 eV and 1.08–2.19 eV, respectively. The theoretical fitting of the optical absorption indicates that the present glass system behaves as an indirect gap semiconductor. The origin of the Urbach energy, ΔE, has been associated with the phonon-assisted indirect transitions. The refractive index and optical dielectric constant have been evaluated from the reflection spectra. The density and molar volume are found to depend on the molar concentration of Bi₂O₃. The values of DC electrical conductivity have been measured from 373 to 623 K and the activation energy has been calculated. Theoretical optical basicity has been reported as a function of the Bi₂O₃ content. The variations have been discussed in terms of structural changes.     

Optical constants for Ge30− x Se70Ag x (0 ≤ x ≤ 30 at%) thin films based only on their reflectance spectra

In this paper, different homogenous compositions of Ge_{30? x} Se₇₀Ag _x (0?≤?x?≤?30 at%) thin films were prepared by thermal evaporation. Reflection spectra, R(λ), for the films were measured in the wavelength range 400–2500?nm. A straightforward analysis proposed by Minkov [J. Phys. D: Appl. Phys. 22 (1989) p.1157], based on the maxima and minima of the reflection spectra, allows us to derive the real and imaginary parts of the complex index of refraction and the film thickness of the studied films. Increasing Ag content at the expense of Ge atoms is found to affect the refractive index and the extinction coefficient of the films. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model. Optical absorption measurements were used to obtain the fundamental absorption edge as a function of composition. With increasing Ag content, the refractive index increases while the optical band gap decreases. The compositional dependence of the optical band gap for the Ge_{30? x} Se₇₀Ag _x (0?≤?x?≤?30) thin films is discussed in terms of the chemical bond approach.     

Optical parameters of nanostructured thin films of?electromagnetite Pb1? x Sr x (Fe0.012Ti0.988)O3

Polycrystalline Pb_1−x Sr _x (Fe_0.012Ti_0.988)O₃ (0.2≤x≤0.4) (PSFT) thin films have been grown on fused quartz substrates by metallo-organic decomposition technique. The grown films were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), source meter and UV–Vis–NIR spectrophotometer to determine the structural, microstructural, dc resistivity and optical properties. The XRD pattern confirmed that the PSFT films has distorted tetragonal single phase, which close to cubic at higher Sr concentration. AFM analysis revealed that the grains size reduces with increasing Sr concentration and their average values lies in the range of 26–9 nm. The higher values of dc resistivity of PSFT nano grains indicate that the transmission of light occurs within these grains up to short wavelength. The refractive index and the extinction coefficient were determined from the optical transmission spectrum in the wavelength range of 200–1100 nm and compared with that theoretically calculated, when fitted to a single oscillator model. The values of optical band gap were determined from Tauc’s extrapolation fitting and suggests that the transformation of electrons during transmission of light through local states within Fermi gap.