Optical parameters measurement for diagnostic and photodynamic therapy of human cervical adenocarcinoma (HeLa) cell line

The purpose of this study was to investigate the optical properties, absorption coefficient (μ _a ) scattering coefficient (μ _s ) and refractive indices, (n) of HeLa cell line in a suspension of 2% minimum essential medium (MEM) at two different (632.8 and 532.0 nm) wave lengths of laser light. Optical properties were determined with Kubelka Munk Model (KMM) and refractive index measurement was made through minimum angle of deviation method (MAD). We reported μ _a = 8.643 ± 0.187 and 2.348 ± 0.249 cm⁻¹ and μ _s = 5.609 ± 0.287 and 88.166 ± 2.833 cm⁻¹ at 632.8 and 532.0 nm, respectively. Refractive index was found to be 1.332 and 1.312 at 632.8 nm and 532.0 nm, respectively. The discussed results provide a route of information for clinical diagnosis, therapeutic application and dosimetry studies in HeLa and other cell lines.     

Thermal tuning of surface plasmon resonance: Ag gratings on barium strontium titanate thin films

Surface plasmon tuning via thermally induced refractive index changes in ferroelectrics is investigated. Epitaxial (Ba_0.7Sr_0.3)TiO₃ (BST) thin films were deposited on MgO (001) substrates by pulsed laser deposition. The refractive index of BST thin films measured by the prism-coupling technique was found to increase from 2.3932 (TE)/1.9945 (TM) at room temperature to 2.3949 (TE)/1.9965 (TM) at 66°C. Then 30-nm-Ag gratings with periodicity 750 nm and width 300 nm were fabricated on BST by soft ultraviolet nanoimprint lithography and subsequent lift-off process. The reflection spectra from 500 to 1000 nm with incident angle from 5° to 60° were measured at room temperature and 66°C, with a collimated and p-polarized light incident perpendicularly to the grating direction. Several modes were observed from the spectra. At 66°C, a red shift of a dip at about 850 nm by 2 nm was obtained at an incident angle of 15°. Calculations confirmed that the observed modes belong to the (−1), (2), (−2) and (3) surface plasmon modes from the Ag and BST interfaces and localized mode; the red shift by thermal tuning is also confirmed. The results indicate the feasibility of active modulation in surface plasmon resonance in solid-state structures.     

Confrontation of nucleus deformation and multipole mixture parameters in (2+0 n ?2+01) transitions with rotational band structure for K π = 0 2+ and 0 3+

The difference of the energies of levels Δ _n = E _lev(2⁺0 _n ) − E _lev(0⁺0 _n ) at n = 1, 2, and 3 and the multipole-mixture parameter δ for (2⁺0₂−2⁺0₁) and (2⁺0₃−2⁺0₁) transitions are contrasted against the structure of the K ^π = 0₂⁺ and 0₃⁺ rotational bands that was calculated on the basis of the quasiparticle-phonon model. The values of (Δ₂ − Δ₁), (Δ₃ − Δ₁), and (Δ₂ − Δ₃) are found to correlate with the sign of the parameter δ and with the calculated structure of the K ^π = 0₂⁺ and 0₃⁺ bands. Original Russian Text ? A.M. Demidov, L.I. Govor, V.A. Kurkin, I.V. Mikhailov, 2009, published in Yadernaya Fizika, 2009, Vol. 72, No. 2, pp. 236–240.     

Mott-insulator-superfluid-liquid transition in a one-dimensional bosonic Hubbard model: Quantum Monte Carlo method

The values of the insulator gap Δ in one-dimensional systems of interacting bosons described by the Hubbard Hamiltonian are calculated at low temperatures by the quantum world-line Monte Carlo algorithm. The dependence of Δ on the size of the system, the temperature, and the parameters of the model is investigated. It is shown that a chain with N _a=50 sites is already sufficient to estimate the thermodynamic value of the critical quantity (t/U)_c for which a transition from the insulator into the superfluid state occurs in a commensurate system. To within the computational error, this value, (t/U)_c=0.300±0.005, agrees with the value (t/U)_c=0.304±0.002 obtained previously by the combined “exact diagonalization + renormalization-group analysis” method. The characteristic Kosterlitz-Thouless behavior of the insulator gap is demonstrated near the critical region: Δ∼exp[−b(1−t/t _c)^−1/2]. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 2, 92–96 (25 July 1996)     

z-Scan characterization of zwitterionic chromophores for optoelectronic switching

Single beam z-scan measurements have been made on films containing amorphous polycarbonate and the zwitterionic chromophore, PYR-3, that has a very high second order nonlinear optical (NLO) figure of merit. The third order NLO figure of merit is ≈1.6 at 1030 nm and is comparable to that found in organic compounds optimized for high n ₂ values. The two-photon absorption coefficient is 2.1×10⁻¹² m/W, which is very low and advantageous for NLO device applications. The third order NLO refractive index is −1.4×10⁻¹⁸ m²/W.     

Trap-centers of self-interstitials in silicon

Deep-level profiles were measured radially acrossn-type FZ silicon wafers containing A-swirl defects by applying DLTS to an array of Schottky contacts. The trapparameters were obtained very accurately using a computer-fit procedure for the full DLTS peaks. Two acceptor levels atE _c −0.49 eV (σ _n =6.6×10⁻¹⁶cm²) andE _c −0.07 eV (σ _n =4.6×10⁻¹⁶cm²) were observed, which varied oppositely to the A-swirl defect density. At short ranges (1–2mm) the trap concentration-profile was smeared out and did not follow the strong fluctuations in the etch pattern. Both levels were measured together with the same concentration. The profiles indicate outdiffusion. A level atE _c −0.14 eV (σ _n =1.1×10⁻¹⁶cm²) was not related to A-swirl defects. A level atE _c −0.11 eV (σ _n =1.1×10⁻¹⁵cm²) was only detected in one ingot. The properties of the deep level atE _c −0.49 eV are discussed in the light of published DLTS results reported for γ-irradiation, laser annealing after self-implantation, annealing under pressure and oxidation of silicon samples. It is concluded, that this level is related to interstitial silicon rather than to an impurity.     

Nonlinearity of refractive index in glasses based on heavy metal oxides with different lead and tellurium contents

We have studied the nonlinearity of the refractive index at a wavelength of 1.08 μm for optical lead silicate and lead phosphate tellurite glasses of different compositions. We have shown that the nonlinear refractive index n₂ increases as the lead content increases in lead silicate glasses and as the tellurium content increases in lead phosphate tellurite glasses, where the latter are typically have higher values of n₂, as high as 24·10⁻¹³ cgs units (47·10⁻¹⁶ cm²/W), and lower Rayleigh losses. We have established a correlation between the nonlinear refractive index and the microstructure of the studied glasses. The highly nonlinear glasses are distinguished by extensive fluctuations in the heavy metal oxide concentration which are “frozen” during cooling of the glass melt. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 780–784, November–December, 2007.     

Laser induced memory bits in photorefractive LiNbO3 and LiTaO3

We study experimentally the formation of refractive index voxels (volume elements) in photorefractive LiNbO₃ and LiTaO₃ crystals illuminated with high irradiance femtosecond laser pulses. We used 150 fs pulses at 800 nm wavelength (energy 6–50 nJ) tightly focused inside the crystals in a single shot regime. This resulted in a formation of a micrometer size region of elevated refractive index, which may be used as memory bits in information storage/retrieval application. The maximum refractive index change of 5×10⁻⁴ was recorded in undoped LiNbO₃ at an average light intensity of ∼TW/cm² that is close to the breakdown threshold. A simple setup for photorefractive recording and in situ monitoring of the refractive index changes has been proposed. M. Sūdžius leaves from: the Institute of Materials Science and Applied Research of Vilnius University, Lithuania.     

Spectroscopy of quasiparticle excitations of superconducting bismuth cuprate at high pressures

We study the energy spectrum of Bi2223 (Bi_1.6Pb_0.4Sr_1.8Ca_2.2Cu₃O_x) at high hydrostatic pressures by Andreev-and tunneling-spectroscopy methods. We determine the gap anisotropy in the basal ab plane and find the following values for the parameters Δ(ϕ): Δ_max=42 mV, and Δ_min=19.5 mV (T _c =110 K and dT _c /dP=0.16 K/kbar). We detect an increase in the ratio R=2Δ_max/kT _c with pressure P; for Bi2223 cuprate, dR/dP≈0.017 kbar⁻¹. In the phonon-frequency region we detect a “softening,” due to pressure, of the high-frequency part of the phonon spectrum corresponding to “breathing” modes of oxygen, as well as other optical modes of Cu-O. The characteristic frequencies of the spectrum for ℏΩ>60 mV are found to decrease, with increasing pressure, at a rate d ln(ℏΩ)/dP≈−6.5±0.5×10⁻³ kbar⁻¹. This result explains the observed increase in the ratio 2Δ/kT _c (P) in the model of strong electron-phonon interaction. Zh. éksp. Teor. Fiz. 113, 1397–1410 (April 1998)     

Spontaneous photorefractive effect in Sr1−x CaxTiO3 (x=0.014)

The temperature dependence of the principal values of the refractive index in Sr_1−x Ca_xTiO₃ (x=0.014) has been measured in the 17–275 K range under various conditions of sample illumination with 1.96 eV photons. The spontaneous photorefractive contribution δn ^ph to the temperature-induced variation of the refractive index of Sr_1−x Ca_xTiO₃, which appears after illumination of the sample in the ferrophase (transition temperature T _c=32 K) and persists in the paraphase under heating up to 150 K, has been separated. The photoinduced polarization has been estimated. Fiz. Tverd. Tela (St. Petersburg) 39, 711–713 (April 1997)     

Suppression of Polarization Dependence in the Design of a 11×11 Polymer/Si Arrayed Waveguide Grating

In this paper we report an effective work of polarization independence in the design of a 11×,11 polymer arrayed waveguide grating (AWG) multiplexer. Theoretical analysis of the polarization properties is given by using Marcatili method. Numerical simulations are performed for independent polarization and single-mode propagation of a rectangular waveguide and bent waveguide with various geometries. The polarization dependence of the AWG device is successfully suppressed by controlling the relative index difference (Δn) between the core and the cladding, ratio between the core width and thickness (a/b), and bent radius of arrayed waveguides, considering practical technical error. The transmission characteristics of two AWGs for two parameter groups of Δn = 1%,a/b = 2 and Δn = 0.8%, a/b = 1.5, show the wavelength shift of 3.5 and 0.02 nm, respectively. The later group of data, which is used in our work, strongly supports the optimum design that we have identified for the birefringence suppression.     

Aggregation of 1,3,7-trimethylxanthine with methylene blue in aqueous solution

We have studied self-association of aromatic molecules of the thiazine dye methylene blue in aqueous solution, using a dimer model. We have determined the dimerization equilibrium constant for the dye molecules K_D = 3900 ± 800 M⁻¹ at T = 293 K. We have decomposed the experimental spectrum into dimer and monomer components. Using the ratio of the molar absorption coefficients for two absorption bands of the dimer spectrum, we obtained the “average” value of the angle between the electronic transition moments of the molecules in the dimers, α = 48°. We have studied heteroassociation of methylene blue (MB) and 1,3,7-trimethylxanthine (caffeine) molecules in aqueous solution. We have calculated the heteroassociation constant as 200 ± 34 M⁻¹. We conclude that heteroassociation of methylene blue and caffeine molecules leads to a lower effective dye concentration in solution, which hypothetically may affect its biological activity. We have determined the values of the Gibbs free energy, the enthalpy, and the entropy for dimerization of methylene blue molecules: ΔG₂₉₃ = −(20 ± 3) kJ/mol, ΔH = −(25 ± 9) kJ/mol, Δ S₂₉₃ = −(17 ± 6) J/mol·K; and for methylene blue-caffeine heteroassociation: ΔG₂₉₃ = −(13 ± 3) kJ/mol, ΔH = −(14 ± 10) kJ/mol, ΔS₂₉₃ = −(2.4 ± 0.2) J/mol·K, respectively. We have shown that the methylene blue aggregates and the heteroassociates with caffeine are predominantly stabilized by dispersion interactions between the chromophore molecules in the associates. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 158–163, March–April, 2006.     

Nonlinear optical properties of nanometer-size silver composite azobenzene containing polydiacetylene film

Diacetylene monomer containing p-nitrophenyl azobenzene moiety (NADA) was synthesized. Silver nanoparticles with different concentrations were adulterated in the above polymerized NADA (PNADA) films and the third-order nonlinear optical properties were investigated in detail. UV–vis spectra and transmission electron microscopy were used to confirm the formation of PNADA/Ag nanocomposite films. The silver nanoparticles (average size of 10 nm) were well dispersed in the polymer films. The value of the nonlinear refractive index n ₂ for PNADA films (8.48×10⁻¹⁵ cm²/W) was much higher than that of pure polydiacetylene films. Further, the introduction of silver nanoparticles into the PNADA polymer films led to the further enhancement of nonlinear optical properties. The maximum value of n ₂ for PNADA/Ag nanocomposite films could be 11.6×10⁻¹⁵ cm²/W. This enhancement should be ascribed to the surface plasmon resonance of silver nanoparticles.     

Determination of the 1S0 neutron-neutron scattering length in the nd breakup reaction at energies in the range En = 40?60 MeV

The first results are obtained in a kinematically complete experiment devoted to measuring the n + d → p + n + n reaction yield at energies in the range E _n = 40−60 MeV and various angles of divergence of two neutrons (Δθ = 4°, 6°, and 8°) in the geometry of neutron-neutron final-state interaction. The ¹ S ₀ neutron-neutron scattering length a _nn is determined by comparing the experimental energy dependence of the reaction yield with the results of a simulation in the Watson-Migdal approximation, which depend on a _nn . For E _n = 40 MeV and Δθ = 6° (the best statistics in the experiment), the value a _nn = −17.9 ± 1.0 fm was obtained. A further improvement of the experimental accuracy will make it possible to remove the existing disagreement of the results from different experiments.     

Field dependence of spin-lattice relaxation of Nd3+ ions in Y3Al5O12 crystals

Our studies involve measuring spin-lattice relaxation times for Nd³⁺ ions in yttrium-aluminum garnets over the temperature range 4–50 K at 9.25 and 36.4 GHz for different orientations of the external magnetic field in relation to the crystallographic axes. The temperature dependence of the relaxation rate is described by T ₁ ⁻¹ =AT ⁿ+b exp(−Δ/kT), where n varies from sample to sample, with n=1 for “perfect” samples (i.e., with the longest relaxation times). Here Δ is approximately 130 cm⁻¹, which is the energy of the excited Kramers doublet of the neodymium ion closest to the ground state, and this makes it possible to interpret the second term in T ₁ ⁻¹ as the contribution of two-stage relaxation proceeding through the intermediate level Δ. A strong field dependence of these processes has been discovered: when the frequency was increased fourfold, the relaxation rate increased by a factor of 10. The effect is a specific manifestation of the degeneracy of the excited level, breaking of the symmetry of the crystalline field due to lattice defects, and the prevalence of deformations of a certain type in the spin-lattice interaction. Zh. éksp. Teor. Fiz. 111, 332–343 (January 1997)     

Dispersion of the Voigt effect in the magnetic semiconductors Cd1−x MnxTe

Spectral measurements of the Voigt birefringence Δn were performed for the cubic magnetic semiconductor Cd_1−x Mn _x Te (0≤x≤0.52) in order to investigate how the exchange interaction of Mn²⁺ ions with itinerant electrons depends on the electron wave vector. It was determined that Δn/x ² is independent of x and the magnetic field direction, i.e., the effect is due to the Mn²⁺ ions and is isotropic. Below the band gap edge the dispersion of the birefringence Δn can be described well in all samples by the unusual dependence Δn∼(E _g −ℏω) ^−3.5. This can be explained by a decrease of the exchange interaction of Mn²⁺ ions with itinerant electrons with increasing distance from the center of the Brillouin zone. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 569–573 (25 April 1998)     

The temperature and light intensity dependence of photorefraction in LiNbO3

In the paper the dependence of the photorefraction (PhR) in LiNbO₃ and LiNbO₃−Fe (0.1 wt%, 0.3wt%) crystals on light intensity (within 10¹⁶–10²³ quanta·cm⁻²·s⁻¹ at wavelengths 496.5 nm and 600 nm) and temperature (in the region 100–500 K) is studied. For all the crystals the limiting values of PhR are similar and atT=293 K Δn _sat ^lim ≈3·10⁻³. In LiNbO₃ the temperature dependence of PhR in the range 100–500 K requires to take into account at least two trapping centres.     

Thin TiO2 grown by metal–organic chemical vapor deposition on (NH4)2S x -treated InP

The electrical characteristics of thin TiO₂ films prepared by metal–organic chemical vapor deposition grown on a p-type InP substrate were studied. For a TiO₂ film of 4.7 nm on InP without and with ammonium sulfide treatment, the leakage currents are 8.8×10⁻² and 1.1×10⁻⁴ A/cm² at +2 V bias and 1.6×10⁻¹ and 8.3×10⁻⁴ A/cm² at −2 V bias. The lower leakage currents of TiO₂ with ammonium sulfide treatment arise from the improvement of interface quality. The dielectric constant and effective oxide charge number density are 33 and 2.5×10¹³ cm², respectively. The lowest mid-gap interface state density is around 7.6×10¹¹ cm⁻² eV⁻¹. The equivalent oxide thickness is 0.52 nm. The breakdown electric field increases with decreasing thickness in the range of 2.5 to 7.6 nm and reaches 9.3 MV/cm at 2.5 nm.     

The estimates of periodic potentials in terms of effective masses

LetG _n=(A _n ⁻ , A _n ⁺ ),n≧1, denote the gaps,M _n ^± be the effective masses and Σn=[A _n−1 ⁺ ,A _n ^- ],A ₀ ⁺ =0, be the spectral bands of the Hill operatorT=−d ²/dx ²+V(x) inL ² (R), whereV is a 1-periodic real potential fromL ²(0,1). Let the length gapL _n=|G_n|, h_n be the height of the corresponding slit on the quasimomentum domain and Δ_n=π²(2n−1)−∣Σ_n∣>0 be the band reduction. Let ,n≧1, denote the gap length for the operator . Introduce the sequencesL={L_n}, h={h_n}, l={l_n}, Δ={Δ_n},M ^±={M _n ^± } and the norms ,m≧0. The following results are obtained: i) The estimates of‖V‖, ‖L‖, ‖h‖ ₁, ‖l‖₁, ‖δ‖ in terms of ‖M^±‖₂, ii) identities for the Dirichlet integral of quasimomentum and integral of potentials and so on, iii) the generation of i), ii) for more general potentials. The research described in this publication was made possible in part by grant from the Russian Fund of Fundamental Research and INTAS.