Determination of the refractive index over a wide wavelength range through time-delay measurements of femtosecond pulses

We present a simple method to measure the refractive index dispersion over a broad wavelength range (0.6-1.6 μm). In a first step, the optical group indices are obtained by measuring the time-retardation of tunable 150 fs laser pulses within a sample relative to air. The refractive index dispersion is then calculated using a Sellmeier equation that describes the measured group index dispersion. We show that our experimental data agree with previously published results to within 2 × 10⁻⁴ for a 3 mm thick sample of fused silica and to within 3 × 10⁻³ for the index n₁ of a 2 mm thick crystal of the highly dispersive and anisotropic organic crystal 4-N,N-dimethylamino-4′-N′-methyl stilbazolium tosylate (DAST).     

Estimation of glucose absorption spectrum at its optimum pathlength for every wavelength over a wide range

ABSTRACT

A method to estimate the absorbance spectrum caused by the variation in the concentration of a substance in a medium at the optimum pathlength for every wavelength on a wide waveband without adjusting the cell’s size precisely was presented in the paper. This spectrum could be used to evaluate the absorption of certain substance at the optimum pathlength at each wavelength, instead of using a uniform pathlength like absorption coefficient. And the absorbance spectra of glucose in aqueous solution at optimum pathlength for every wavelength at 900–2500?nm were estimated by using this method. Moreover, the glucose absorbance spectra show an unexpected result that the absorption peaks at different overtones of the oxygen–hydrogen and carbon–hydrogen bonds are of similar amplitudes.     

Dynamics of sorbitol and maltitol over a wide time-temperature range

The relaxation behaviour of two molecular glass-forming systems, namely sorbitol and maltitol, are investigated in the large temperature range relevant to the glass-transition. These data are obtained by combining three techniques, i.e. low-frequency mechanical spectroscopy, medium and high frequency dielectric spectroscopy, and viscosity measurements. This procedure allows to determine the relaxation map of these polyols on a wide time range [10^-9-10⁷ s]. Two different relaxation processes can be observed. The principal α-relaxation process exhibits a complex behaviour, comprising a non-Arrhenius temperature dependence above T _g (supercooled liquid state), and an Arrhenius behaviour below T _g (glassy state). A secondary β-relaxation is observed at higher frequencies with an Arrhenius temperature dependence. The secondary process appears in the same time-temperature range in both polyols. Consequently the molecular root of this relaxation is most likely the same in these complementary chemical systems. On the other hand, the time scale on which the α and β processes cross is very different for these two polyols. We relate this feature to the differences in the relative contributions of intra and inter-molecular interactions due to the different chemical architecture of these polyols.     

Study on optical electron polarimeter and measurement of the relative Stokes parameters of weak light

In this paper, we present the research on an optical electron polarimeter, which is used to determine the polarization of an incident electron beam by measuring the relative Stokes parameters of the fluorescence emitted from the He gas following the impact excitation with the electron beam. The fundamental theory of the optical electron polarimeter is discussed with the 3³P→2³S transition of He. The structure and performance of the instrument are described, which are different in some aspects from previous works. The arrangement of the experiment for measuring the relative Stokes parameters of linearly polarized weak light is also investigated, which actually involves the same processes as the polarization measurement with the incident electron beam. The results obtained are in agreement with the theoretical prediction.     

Accurate measurement of the cutoff wavelength in a microstructured optical fiber by means of an azimuthal filtering technique

A simple self-referenced nondestructive method is proposed for measuring the cutoff wavelength of microstructured optical fibers (MOFs). It is based on the analysis of the time-dependent optical power transmitted through a bow-tie slit rotating in the far-field pattern of the fiber under test. As a first demonstration, the cutoff wavelength of a 2 m MOF sample is found to be close to that provided by numerical predictions (approximately 25 nm higher). Because of the high dynamics of the measurement, the uncertainty is limited to Dlambda= +/-10 nm.     

Total light absorption in a wide range of incidence by nanostructured metals without plasmons

Metals structured by nanocavities have recently been demonstrated to efficiently absorb light in a wide range of angles of incidence. It has been assumed that nanovoid plasmons are at the origin of the strong absorption. It is shown that it is possible to totally absorb incident light without plasmons. To avoid their excitation, a diffraction grating consisting of cylindrical cavities in a metallic substrate is illuminated in transverse electric polarization. It is found that cylindrical cavities can sustain cavity resonances with a high enhancement of the light intensity, provoking a total absorption of light in a wide range of incidence.     

Deformation resistance and fracture of iron over a wide strain rate range

The results of measurements of the decay of an elastic precursor in iron at the distances from 0.13 to 10 mm and the spall strength of the samples with such thicknesses have been compared with similar data for the nanometer-scale samples. The decay has been described by a unique dependence whose differentiation gives the relationship between the initial plastic strain rate in the range from 10³ to 10⁹ s^?1 and the compression stress in the elastic shock wave from 1.5 to 27.5 GPa. The dynamic breaking strength (spall strength) varies in this range of shock-wave load time from 1.5 to 20 GPa.     

Highly nonlinear optical fibre loop mirror for reshaping femtosecond pulses from a soliton-compressed electro-absorption modulator source over a wide repetition rate and wavelength range

Highly nonlinear fibre (HNF) applied to a nonlinear optical fibre-loop mirror (NOLM) proves very effective for high quality femtosecond pulses shaping. The HNF exhibiting about four times larger nonlinearity than either dispersion flattened fibre or dispersion-shifted fibre excites higher-order soliton propagation enabling significant pulse compression, while shortening the loop length required for efficient switching, which advantageously reduces both the detrimental higher-order chromatic dispersion effects and sensitivity to environmental perturbations. A short NOLM consisting of a 60 m HNF demonstrates effective reshaping and compression of 254–394 fs pulses from a fibre-soliton compressed electro-absorption modulator source to produce pedestal-free and transform-limited 186–243 fs pulses over a wide wavelength (1550–1570 nm) and repetition-rate (6.8–18 GHz) range.     

Thermal and physical properties of sodium niobate ceramics over a wide temperature range

The temperature dependences of the heat capacity C _p (T) and thermal expansion coefficient α(T) of NaNbO₃ ceramic samples have been investigated in the temperature range from 2 to 800 K. In addition to the anomalies associated with the known phase transitions at temperatures T ₆ ≈ 265 K, T ₅ ≈ 638 K, T ₄ ≈ 760 K, and T ₃ ≈ 793 K, anomalies in the behavior of C _p (T) and α(T) have been observed near T _5″ ≈ 500 K and T _5′ ≈ 600 K. It has been found that all the observed structural transformations, according to the values of the entropy change, are not related to the ordering of structural elements. It has been shown that, with an increase in the temperature, the unit cell volume during the phase transitions near 265, 515, 604, and 638 K decreases. The specific features of the transition to the phase R3c have been examined. Two possible scenarios of the sequence of phase transformations in the temperature range between T ₅ and T ₆ have been analyzed.     

Simultaneous measurement of surface shape and absolute optical thickness of a glass plate by wavelength tuning phase-shifting interferometry

The absolute optical thickness and the surface shape of a glass plate of 7-in. square and 3.1mm thick was simultaneously measured by three-surface interferometry using a wavelength tuning Fizeau interferometer. The wavelength of a tunable diode laser is scanned linearly from 632 to 642 nm, at which the initial and the final phases of the interference fringes for the surface shape and for the optical thickness were separated and measured by a tunable phase-shifting technique. The number of phase variations in the interference fringes during the scanning is counted by discrete Fourier analysis, in which systematic errors caused by a nonlinearity in the wavelength scanning is corrected by a correlation analysis between the observed and theoretical interference fringes. Experimental results demonstrate that the systematic errors in the measured value were 15 nm for the surface shape and 0.6 μm for the absolute optical thickness.     

Production and investigation of a stationary thermal air plasma over a wide pressure and temperature range

An arrangement is described for generating at various pressures a filamentary, axially symmetric thermal arc of high stability. The arc's composition is wholly determined by the initial composition of the gas used. The radial temperature distribution of the arc in air was studied over the pressure range from 0.26 to 6 atm. At a current of 10 amps., the temperature in the axial region of the arc in air varies between 15 000 and 20 000° K, depending upon the pressure. At a distance of 0.4–0.5 mm from the axis of the discharge, the temperature drops to 5000° K.In conclusion, the authors wish to express their sincere gratitude to M. A. El'yashevich for his interest.     

Experimental and semi-detailed kinetic modeling study of decalin oxidation and pyrolysis over a wide range of conditions

Decalin is the simplest polycyclic alkane (polynaphtenic hydrocarbon) found in liquid fuels (jet fuels, Diesel). In order to better understand the combustion characteristics of decalin, this study provides new experimental data for its oxidation in a jet-stirred reactor. For the first time, stable species concentration profiles were measured in a jet-stirred reactor at a constant mean residence time of 0.1 s and 0.5 s at respectively 1 and 10 atm, over a range of equivalence ratios (? = 0.5–1.5) and temperatures (750–1350 K). The oxidation of decalin under these experimental conditions was modeled using a semi-detailed chemical kinetic reaction mechanism (11,000 reactions involving 360 species) derived from a previously proposed scheme for the ignition of the same fuel in a shock-tube. The proposed mechanism that includes both low- and high-temperature chemistry shows reasonably good agreement with the present experimental data set. It can also represent well decalin pyrolysis and oxidation data available in the literature. Reaction path analyses and sensitivity analyses were conducted to interpret the results.     

Optical-frequency dependent modal birefringence and polarization mode dispersion of birefringent single-mode optical fibers over a broadband optical wavelength range

Optical-frequency dependent polarization mode dispersion as well as modal birefringence of three kinds of specially designed hollow-induced birefringent single-mode fiber are measured over an optical frequency range between 345 and 410 THz by optical frequency-domain interferometry.     

Computer simulation of the structure of liquid cesium and determination of the pair potentials over a wide temperature range

Using diffraction data for liquid cesium structure over a wide temperature range, models of liquid cesium are constructed and the effective pair potentials are extracted using the theory of liquids. The iterative procedure proposed by L. Reatto is used. In the range 323-1923 K the pair potentials are weakly temperature-dependent. The potentials extracted from the diffraction data differ from the potentials calculated using the Animalu-Heine pseudopotential. The self-diffusion coefficients in liquid cesium are determined. Their temperature dependence is described satisfactorily by a power-law function. Zh. éksp. Teor. Fiz. 115, 50–60 (January 1999)     

Analytical approximation of the thermal and caloric equations of state for real gases over a wide density and temperature range

The thermal and caloric equations of state of the main components of gas mixtures normally used in calculations of gas dynamic processes, including combustion and detonation, as well as in problems of internal ballistics, are presented in an analytical form. The formulas obtained for the equations of state contain a relatively small number of parameters and provide an average error of approximation of less than 1% at temperatures from 500 to 2000–2500 K and densities up to the critical.     

Influences of supply voltage on single event upsets and multiple-cell upsets in nanometer SRAM across a wide linear energy transfer range

The influences of reducing the supply voltage on single event upset(SEU)and multiple-cell upset(MCU)in two kinds of 65-nm static random access memories(SRAMs)ar...     

Transformation and measurement of parameters of gaussian,laguerre-gaussian,and super-gaussian beams by using a light filter based on absorbing axicon

Properties of a new optical element — light filter based on the absorbing axicon are studied. The filter allows determining the parameters of radially-symmetric laser beams, producing precisely collimated beams, and smooth tuning of the beam power. Transformation of Gaussian, Laguerre-Gaussian, and super-Gaussian beams in the filter is considered. As a result of this transformation doughnut-like and M-like beam profiles are produced.