A spectroscopic prism coupler for measuring the refractive indices and thicknesses of dielectric films

A spectroscopic prism coupler is created for measuring refractive indices n_f and thicknesses H_f of dielectric films. The operating principle of the device is based on the simultaneous resonance excitation of several waveguide modes in a film by a focused TE or TM polarized light beam in the geometry of frustrated total internal reflection. Calculations of n_f and H_f are performed using measured angular positions θ_m of dark m-lines in the cross section of the specularly reflected beam. Using obtained angles θ_m, we can calculate effective refractive indices β_m of modes. By solving a set of nonlinear dispersion equations for the modes of a planar waveguide, we can calculate refractive index n_f and thickness H_f of a film. The proposed prism coupler has no moving parts and allows us to measure the optical parameters of films 0.5–10 μm thick in the 400–1100 nm range of wavelengths. The device can also be used as a spectroscopic refractometer for measuring the refractive indices of bulk media. The device is used to measure refractive index and thickness of a SiO film and the refractive index of TF4 glass.     

Synthesis and optical properties of basic fuchsin dye-doped PMMA polymeric films for laser applications: wide scale absorption band

Basic fuchsin dye-doped poly(methyl methacrylate) polymeric films were sensitized with various dye concentrations ranging from 0.0833 to 1.667 wt% of basic fuchsin. Their structure, linear absorption, and optical limiting properties were examined. The films were prepared using a simple and fast casting technique dissolved in chloroform for both the dye and the polymer. Structural characterizations were achieved by XRD, and the films showed an amorphous hump supporting the noncrystalline structure of studied polymeric composites. Spectrophotometer measurements were used to estimate the spectral absorption measurements of the films such as transmittance, absorbance with the calculations of absorption index (k), and optical energy band gap (E _g ) in the wavelength region from 190 to 2500 nm. Results show that the optical constants change with increasing the dye doping concentrations. It has been found that optical energy gap (E _g ) appearing that, both direct and indirect optical transitions are conceivable for these films. Optical limiting properties of the films with various dye concentrations were studied using a continuous wave He–Ne laser operating at 632.8 nm. The results appeared that the sample has an obvious optical limiting effect. The designed BF/PMMA composites can be applicable in wide-scale applications.     

Influence of the dimension of a polycrystalline film and the optical anisotropy of crystallites on the effective dielectric constant of the film

The dimension D of a polycrystalline film and the optical anisotropy m = ε_z/ε_x of uniaxial crystallites with the principal components ε_x = ε_y and ε_z of the tensor of the dielectric constant have been shown to produce a strong influence on the effective dielectric constant ε_D^* and the effective refractive index n_D^* = (ε_D^*)^1/2 of the film in the optical transparency region, as well as on the boundaries of the intervals B_Dl ≤ ε_D^* ≤ B_Du. The intervals Δ₂(m) = B_2l–B_2u and Δ₃(m) = B_3l–B_3u are separated by a gap for m in the range 1 < m < 2, whereas the theoretical dependence ε₂^*(m) is separated by a gap from the interval Δ₃(m) for m in the range 1 < m < 4. This is confirmed by a comparison of the experimental (n_oP) and theoretical (n_D^*) ordinary refractive indices for uniaxial polycrystalline films of the conjugated polymer poly(p-phenylene vinylene) (PPV) with uniaxial crystallites and appropriate values of m. In the visible transparency region of the PPV films with a change in m(λ) in the range 2 < m(λ) < 3 due to the dependence of the components ε_x,z(λ) on the light wavelength λ, the refractive indices n_oP²(λ) = ε_oP(λ) are consistent with the theoretical values of ε₂^*(λ) and lie outside the interval Δ₃(m). For m(λ) > 3 near the electronic absorption band of the crystallites, the values of ε_oP(λ) lie in the region of the overlap of the intervals Δ₂(m) and Δ₃(m). The boundaries mc of the range 1 < m < m_c are determined, for which the interval Δ₂(m) is separated by a gap from the dependences ε₃^*(m) corresponding to the effective medium theory with spherical crystallites and hierarchical models of a polycrystal, as well as from the proposed new dependence ε₃^*(m).     

Effective refractive index of a quasi-two-dimensional polydomain film of a conjugated polymer

The relation between the effective ordinary refractive index n* = (n _o n _e )^1/2 of a quasi-two-dimensional polydomain uniaxial film of a conjugated polymer F8BT in the visible transparency region and the refractive indices (n _o,e ) of uniaxial domains with the optical axes randomly oriented in the plane of the film has been confirmed experimentally. The permissible interval of variations in n* has been established and a strong spectral dispersion of this interval near the long-wavelength electronic absorption band of the film has been demonstrated.     

Investigation of the optical constants of arsenic chalcogenide films in the wavelength range 0.5–2.5 μm

Thin films of chalcogenide glasses deposited on quartz glass substrates by thermal evaporation in vacuum have been investigated. The dependences n(λ) and k(λ) for films of different composition have been determined from the transmission spectra. Expressions of the n = A + BL + CL ² + Dλ ² + Eλ ⁴ type (L = (λ ² ? 0.028)^?1 and A, B, C, D, and E are constants) for calculating the refractive indices of As₂Se₃, AsSe₄, AsS₄, and AsS_16.2Se_16.2 films in the wavelength range from 0.5 to 2.5 μm are reported.     

Low-temperature spray-pyrolysis of FeS2 films and their electrical and optical properties

Iron disulfide (FeS₂) films with a wide range of electrical resistivities 100 Ω cm ? ρ ? 800 kΩ cm, a high adhesion to the substrate, and a resistance to aggressive media have been prepared by the spray pyrolysis of aqueous solutions of the salts FeCl₃ · 6H₂O and (NH₂)₂CS at low temperatures in the range 250°C ? T _S ? 400°C. It has been found that the FeS₂ films have a high transmittance T ≈ 60–70% and are characterized by a sharp transmission edge. It has been shown that the optical band gap for direct (E _g ^op = 2.19–2.78 eV) and indirect (E _g ^′op = 1.26–1.36 eV) optical transitions depends on the conditions of film preparation.     

Changes in the electronic,optical, and magnetic properties of LaSrMnO films upon transition from the rhombohedral phase to the orthorhombic phase

The properties of LaSrMnO films are investigated in the temperature range of the transition from the rhombohedral phase to the orthorhombic phase (600–650° C). It is shown that, with a variation in the growth temperature T_s, the change in the film properties is governed by the interaction of Mn-O metallic (ferromagnetic) clusters in the dielectric (antiferromagnetic) matrix. At T_s≤600°C, the low density of e _g states and the dielectric gap (E _g =0.3–0.5 eV) are responsible for the following features: (i) the optical transparency in the range ?ω=0.5–2 eV, (ii) the difference between the FC and ZFC magnetizations M(T), (iii) the high resistance, and (iv) the appearance of the portions R(T) ≈ const in the dependence R(T) due to the transformation of clusters into a system of tunnel-coupled quantum dots. At T_s≥650°C, the local increase in the atomic and electronic densities leads to a decrease in the optical transmission and the resistance by three to nine orders of magnitude, the appearance of a maximum and a minimum in the dependences R(T) of the LaSrMnO films, and an increase in the magnetization M(10 K) by one order of magnitude. The inference is drawn that magnetic ordering of the system of tunnel-coupled clusters encourages an increase in the cluster size and in the content of the metallic (ferromagnetic) phase.     

Spin-selective low temperature spectroscopy on single molecules with a triplet-triplet optical transition: Application to the NV defect center in diamond

The spin-selective photokinetics of a single matrix-isolated impurity molecule with a triplet-triplet optical transition, T ₀–T ₁, is considered and the manifestations of the photokinetics in the fluorescence excitation spectra and intensity autocorrelation functions g ⁽²⁾(τ) of the molecule undergoing narrow-band optical excitation is studied to resolve the fine structure of the transition. The rates of intersystem crossings (ISCs) T ₁→S→T ₀ to and from a nonradiating singlet state S of the molecule and the rate of population relaxation among the ground (T ₀) state sublevels can be obtained from the spectra and g ⁽²⁾(τ) using the analytical expressions obtained. New experiments on an individual NV defect center in nanocrystals of diamond, where, for the first time, the fine structure of its triplet-triplet ³ A-³ E zero-phonon optical transition (~637 nm) at 1.4 K was resolved, are interpreted. It is concluded that the rate of the ISC transition from the m _S =0 sublevel of the excited ³ E state to the singlet ¹ A state (~1 kHz) is much slower than the rates from the m _S =±1 substates, while the rates of ISC transitions to different m _S substates of the ground ³ A state are close to each other (~1 Hz). As a result, only the optical transition between m _S =0 sublevels in the ³ A-³ E manifold contributes strongly to the fluorescence. The experimentally observed double-exponential decay of the g ⁽²⁾(τ) function is explained by the two pathways available to the center for it to leave the S state: (i) the S→ T ₀(m _S )=0) transition and (ii) the S→T ⁰(m _S =±1) transitions followed by the slow spin-lattice relaxation T ₀(m _S =±1)→T ₀(m _S =0) (rate ~0.1 Hz). The work is important for studies where the NV center is used as a single photon source or for quantum information processing.     

Precision measurements of optical excitation functions for the mercury atom

We describe a computer-based facility for studying the excitation of atoms by ultramonochromatic electrons and give optical excitation functions for the 12 mercury spectral lines that originate from the n ¹ S ₀, n ¹ P ₁, n ¹ D ₂, n ³ S ₁, n ³ P _j , and n ³ D _j levels. We detected about 100 features in the energy dependences measured from the excitation threshold to 15.5 eV. The previously found positions of the features on the energy scale are in good agreement with our results. Most of the resonant features are shown to be mainly attributable to the decay of short-lived states of the negative mercury ion. We detected a postcollision interaction effect in the optical excitation functions of the lines that originate from the n ¹ S ₀ levels at energies of about 11 eV.     

CeAlO<Subscript>3</Subscript> crystals: Preparation and study of their electrical and optical characteristics

Crystals of cerium aluminate with perovskite structure were obtained using the cold-crucible technique. The electrical and optical properties of cerium aluminate were studied in air in the range 300–1300 K. The main characteristics of CeAlO₃ at T=300 K are a follows: electrical conductivity σ=10^?7 S/cm, dielectric permittivity ?=3000–10000 (both measured at a frequency of 1000 Hz), thermal band-gap width ΔE=2.3±0.5 eV, and optical width δE=2.65±0.25 eV, which decreases at a rate of ?0.62×10^?3 eV/K with increasing temperature in the 300-to 1500-K interval.     

Spectra and mean energies of prompt neutrons from <Superscript>238</Superscript>U fission induced by primary neutrons of energy in the region <Emphasis Type="Italic">E</Emphasis><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript><20 MeV

The time-of-flight technique is used to measure the ratios R(E, E _n )=N(E, E _n )/N_Cf(E) of the normalized (to unity) spectra N(E, E _n ) of neutrons accompanying the neutron-induced fission of ²³⁸U at primary-neutron energies of E _n =6.0 and 7.0 MeV to the spectrum N_Cf(E) neutrons from the spontaneous fission of ²⁵²Cf. These experimental data and the results of their analysis are discussed together with data that were previously obtained for the neutron-induced fission of ²³⁸U at the primary energies of E _n =2.9, 5.0, 13.2, 14.7, 16.0, and 17.7 MeV.     

The Effect of Specular Reflectances on the Interaction of an Electromagnetic <Emphasis Type="Italic">E</Emphasis> Wave with a Thin Metal Film Placed between Two Dielectric Media

The interaction of an electromagnetic E wave with a thin metal film placed between two dielectric media is calculated in the case of different specular reflectances q₁ and q₂ for the reflection of electrons from the surface of the thin metal layer, in the case of variations in the values of dielectric permittivities ε₁ and ε₂ of the media, and in the case of different values of angle of incidence θ of the electromagnetic wave. The behavior of reflection coefficient R, transmission coefficient T, and absorption coefficient A in relation to the frequency of the external field is analyzed.     

An optical study of vacuum evaporated amorphous Ge<Subscript>20</Subscript>Te<Subscript>80−<Emphasis Type="Italic">x</Emphasis></Subscript>Bi<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films using transmission and reflection spectra

The present paper reports the effect of Bi addition on the optical behavior (optical band gap and refractive index) of Ge₂₀Te_80?x Bi _x (where x=0, 1.5, 2.5, 5.0) glassy alloys by analyzing the transmission and reflection spectra of their thin films in the 900–2400 nm range. Films are deposited on glass substrate using a thermal evaporation technique under vacuum. Various optical parameters viz. refractive index, extinction coefficient, absorption coefficient, optical band gap, etc. are determined and the effect of Bi incorporation on these parameters is studied. The refractive index has been found to increase with increasing Bi content over the entire spectral range and this behavior is due to the increased polarizability of the larger Bi atomic radius (1.46 Å) compared to Te atomic radius (1.36 Å). Dispersion energy, E _d , average energy gap, E ₀ and static refractive index, n ₀ is calculated using Wemple–DiDomenico model. Optical band gap is estimated using Tauc’s extrapolation and is found to decrease from 0.86 to 0.73 eV with the Bi addition. This behavior of the optical band gap is interpreted in terms of the electronegativity difference of the atoms involved and the cohesive energy of the system.     

Thermal annealing effect on structural and optical properties of 2,9-Bis [2-(4-chlorophenyl)ethyl] anthrax [2,1,9-def:6,5,10-d′e′f′] diisoquinoline-1,3,8,10 (2H,9H) tetrone (Ch-diisoQ) thin films

Thin films of 2,9-Bis [2-(4-chlorophenyl)ethyl] anthrax [2,1,9-def:6,5,10-d′e′f′] diisoquinoline-1,3,8,10 (2H,9H) tetrone (Ch-diisoQ) were prepared by thermal evaporation technique. Structural properties of these (as-prepared and annealed at 373, 423, 473 and 523 K) films were determined by X-ray diffraction and scanning electron microscopy, which showed that the grain sizes increasing by the annealing effect. The transmittance and reflectance of all Ch-diisoQ thin films were measured in the range 200–2500 nm. Some optical constants such as optical band gap (E _g ), dispersion energy (E _d ), single oscillator energy (E _o ) and optical dielectric constant at a higher frequency (ε _∞ ) were calculated at different annealing temperatures. The optical band gap of the samples is decreased with the increase of annealing temperatures due to the increasing of the π-dislocation. Finally, the values of the optical susceptibility, χ⁽³⁾, were found to be annealing dependence.     

Photorefractive polymer composites for the IR region based on carbon nanotubes

The photorefractive properties of polymer composites based on aromatic polyimide and single-wall carbon nanotubes are studied using radiation at a wavelength of 1064 nm. It is found that the nanotubes possess photoelectric sensitivity in this spectral region and that the kinetic photorefractive characteristics of the polymer composites are entirely determined by the photogeneration and charge transport characteristics of the layers. The two-beam gain coefficient of the signal beam measured for a composite consisting of aromatic polyimide and 0.25 wt % of single-wall carbon nanotubes in a constant electric field E₀ = 79 V/μm is equal to 84 cm^?1 and exceeds the optical absorption coefficient by 59 cm^?1. The refractive index modulation is equal to Δn = 0.004 at E₀ = 54 V/μm.     

Magnon satellite bands in the optical spectrum of antiferromagnetic Rb<Subscript>2</Subscript>MnCl<Subscript>4</Subscript>

The evolution of optical absorption in a two-dimensional antiferromagnet is investigated in the range of the transition ⁶A_1g → ⁴A_1g, ⁴E _g (⁴G) observed in manganese ions in an external magnetic field inducing noncollinearity of the magnetic structure. It is revealed that hot and cold satellites of the exciton-magnon bands appear in the optical absorption spectrum and then increase in intensity. The shapes of the magnon satellite bands corresponding to a two-dimensional magnetic structure are calculated. It is demonstrated that magnons at the inner points of the Brillouin zone appreciably contribute to the absorption. The zero-point magnetic oscillations play a decisive role in the absorption associated with the magnon decay at low temperatures.     

Behavior of the Elastic-Scattering Cross Section <Emphasis Type="Italic">σ</Emphasis>(<Emphasis Type="Italic">E</Emphasis>) in the Vicinity of Two Overlapping Levels with Equal Resonance Energies

The elastic-scattering process proceeding through two resonance levels that have the same spin j and equal resonance energies, (E₁ = E₂), but different widths (Γ₁ ≠ Γ₂) is considered. It is shown that the energy dependence of the total scattering cross section has two equal maxima at the points E₁ ± (1/2) \(\sqrt {{\Gamma _1}{\Gamma _2}} \), the cross-section value at the maxima being 4π (2j + 1)?², where ? is the wavelength of the incident particle in the c.m. frame, and that, at the energy E₁, the cross section vanishes, σ (E₁) = 0. The cross section is symmetric with respect to the point E₁.     

Influence of pressure on electronic and optical properties of phosphorus-doped ZnO

In this work, the geometrical, electronic structure and optical properties of P-doped ZnO under high pressures have been investigated using first-principles methods. The pressure effects on the lattice parameters, electronic band structures, and partial density of states of crystalline P-doped ZnO are calculated up to 8 GPa. Moreover, the evolution of the dielectric function, absorption coefficient (αω)), reflectivity (R(ω)), and the real part of the refractive index (n(ω)) at high pressure are also presented.     

Electronic and optical properties of Fe<Subscript>2</Subscript>SiO<Subscript>4</Subscript> under pressure effect: ab initio study

We report first-principles studies the structural, electronic, and optical properties of the Fe₂SiO₄ fayalite in orthorhombic structure, including pressure dependence of structural parameters, band structures, density of states, and optical constants up to 30 GPa. The calculated results indicate that the linear compressibility along b axis is significantly higher than a and c axes, which is in agreement with earlier work. Meanwhile, the pressure dependence of the electronic band structure, density of states and partial density of states of Fe₂SiO₄ fayalite up to 30 GPa were presented. Moreover, the evolution of the dielectric function, absorption coefficient (α(ω)), reflectivity (R(ω)), and the real part of the refractive index (n(ω)) at high pressure are also presented.