Development and study of a radiance measurement system based on a CCD array in the vacuum and near ultraviolet region

We describe methods and instrumentation that we have developed for measuring the radiance distribution over the emitting region of plasma emitters in the extreme vacuum ultraviolet region. The radiance comparator for vacuum and near ultraviolet radiation includes a reflecting telescope based on highly reflective nanostructures, a set of filters to eliminate the effect of scattered light and higher orders of diffraction, and a cooled CCD array.     

Three-photon absorption and nonlinear refraction of BaMgF₄ in the ultraviolet region

The nonlinear refraction and nonlinear absorption phenomena are investigated in BaMgF₄ single crystal using the Z-scan technique in the ultraviolet region with a pulsed laser at 400?nm with 1?ps pulse duration. The remarkable nonlinear absorption behavior is identified to be three-photon absorption under the experimental conditions. In addition, both nonlinear refraction and nonlinear absorption have relatively large values and possess small anisotropy along three different crystallographic axes. The large values of nonlinear refractive index are demonstrated through the self-phase modulation effect.     

Optical absorption near the fundamental absorption edge in some vanadate glasses

The fundamental absorption edges of some samples of V₂O₅-P₂O₅ and V₂O₅-P₂O₅-TeO₂ glasses were measured in the short wavelength part of the visible region, and it was found that the fundamental absorption of these glasses is dependent on composition and arises from direct forbidden transitions and occurs at a photon energy in the range 1.9 to 2.6 eV, depending on composition.     

Resonant scattering and mode coupling in two-dimensional textured planar waveguides

A heuristic formalism is developed for efficiently determining the specular reflectivity spectrum of two-dimensionally textured planar waveguides. The formalism is based on a Green's function approach wherein the electric fields are assumed to vary little over the thickness of the textured part of the waveguide. Its accuracy, when the thickness of the textured region is much smaller than the wavelength of relevant radiation, is verified by comparison with a much less efficient, exact finite difference solution of Maxwell's equations. In addition to its numerical efficiency, the formalism provides an intuitive explanation of Fano-like features evident in the specular reflectivity spectrum when the incident radiation is phase matched to excite leaky electromagnetic modes attached to the waveguide. By associating various Fourier components of the scattered field with bare slab modes, the dispersion, unique polarization properties, and lifetimes of these Fano-like features are explained in terms of photonic eigenmodes that reveal the renormalization of the slab modes due to interaction with the two-dimensional grating. An application of the formalism, in the analysis of polarization-insensitive notch filters, is also discussed.     

Interpolation of the spectral responsivity of silicon photodetectors in the near ultraviolet

We improve the methods used to interpolate the responsivity of unbiased silicon photodetectors in the near-ultraviolet region. This improvement is achieved by the derivation of an interpolation function for the quantum yield of silicon and by consideration of this function in the interpolation of the internal quantum efficiency of photodiodes. The calculated quantum-yield and spectral-responsivity values are compared with measurement results obtained by the study of a silicon trap detector and with values reported by other research groups. The comparisons show agreement with a standard deviation of 0.4% between our measured and modeled values for both the quantum yield and the spectral responsivity within the wavelength region from 260 to 400 nm. The proposed methods thus extend the predictability of the spectral responsivity of silicon photodetectors to the wavelength region from 260 to 950 nm. Furthermore, an explanation is proposed for the change in the spectral responsivity of silicon photodiodes that is due to UV radiation. In our improved quantum efficiency model the spectral change can be accounted for completely by the adjustment of just one parameter, i.e., the collection efficiency near the SiO(2)/Si interface.     

Thin-film photodetectors for the vacuum ultraviolet spectral region

We report on thin-film photodetectors optimized for detecting the vacuum UV and rejection of the visible spectrum of electromagnetic radiation. The devices are made of hydrogenated amorphous silicon and silicon carbide on a glass substrate. At room temperature the photodetectors exhibit quantum efficiencies of 52% at lambda = 58.4 nm, 1% at lambda = 400 nm, and 0.1% at lambda = 650 nm. The response time for UV pulses from an N(2) laser gives signals of 6-mus full width at half-maximum and 500-ns rise time.     

Confocal light absorption and scattering spectroscopic microscopy

We have developed a novel optical method for observing submicrometer intracellular structures in living cells, which is called confocal light absorption and scattering spectroscopic (CLASS) microscopy. It combines confocal microscopy, a well-established high-resolution microscopic technique, with light-scattering spectroscopy. CLASS microscopy requires no exogenous labels and is capable of imaging and continuously monitoring individual viable cells, enabling the observation of cell and organelle functioning at scales of the order of 100 nm.     

Anisotropy in the absorption and scattering spectra of chicken breast tissue

Oblique incidence reflectometry is a simple and accurate method for measuring the absorption and the reduced-scattering coefficients of turbid media. We used this technique to deduce absorption and reduced-scattering spectra from wavelength-resolved measurements of the relative diffuse reflectance profile of white light as a function of source-detector distance. In this study, we measured the absorption and the reduced-scattering coefficients of chicken breast tissue in the visible range (400-800 nm) with the oblique incidence probe oriented at 0 degrees and 90 degrees relative to the muscle fibers. We found that the deduced optical properties varied with the probe orientation. Measurements on homogenized chicken breast tissue yielded an absorption spectrum comparable with the average of the absorption spectra for 0 degrees and 90 degrees probe orientations measured on the unhomogenized tissue. The reduced-scattering spectrum for homogeneous tissue was greater than that acquired for unhomogenized tissue taken at either probe orientation. This experiment demonstrated the application of oblique-incidence, fiber-optic reflectometry to measurements on biological tissues and the effect of tissue structural anisotropy on optical properties.     

Broadband near ultraviolet random lasing in ZnO 3-D nanowalls

Broadband near ultraviolet (NUV) random laser was achieved by Au nanoparticle loaded ZnO 3-D nanowalls. Au nanoparticle was loaded on ZnO 3-D nanowalls by photo-chemical deposition method using ionic liquid. The optical confinement by the 3-D nanowalls and enhancement of incident light scattering by Au nanoparticle increase the number of resonant modes, and thus leading to a broadband multiple spectrum random lasing. The results demonstrate an important step towards to expand the application scope of NUV laser on medical imaging of cells, solid-state lighting and optical sensor.     

Critical light scattering in4He near the gas-liquid critical point

Scattered intensities of light were measured near the gas-liquid critical point of ⁴ He at scattering angles of 30, 60, and 90° as functions of the reduced temperature =|T–T _c |/T _c along the critical isochore (T>T _c ) and the coexistence curve (T>T _c ). The temperature range was 3×10 ^–5 <<1.5×10 ^–2 . Critical exponents and coefficients describing divergence of the generalized susceptibility and the correlation length are obtained as (T>T _c )=1.31±0.02, v(T>T _c )=0.66±0.02, ₀ (T>T _c )=4.2±0.6 Å, (T>T _c )=1.32±0.02, v(T>T _c )=0.68±0.02, _± (T>T _c )=2.6±0.7 Å, =0.06±0.06(T>T _c ), 0.05±0.05(T>T _c ), and ₀(T>T _c )/x_± (T>T _c )=3.6±0.4. It is pointed out that the quantal nature of ⁴ He has remarkable influence on the critical behavior of ⁴ He in the above-mentioned temperature region.     

Wavelength dependence of angle-resolved scattering in the extreme-ultraviolet-visible region

The wavelength dependence of p-polarized, angle-resolved scattering has been thoroughly investigated on 12 aluminum films at wavelengths of 160, 325, and 633 nm. The isotropic samples were made by evaporating aluminum films in ultrahigh vacuum onto supersmooth silicon wafers at different temperatures. By further annealing in ultrahigh vacuum, surface roughnesses of ? 5-70 ? rms were obtained, as measured by total integrated scattering. The experimental measurements were carried out in a dedicated angle-resolved scattering system with provisions for operation in vacuum and for illuminationof the same spot on the sample at all three wavelengths. The theoretically expected 1/λ(4) dependence was in reasonable agreement with measured values for the average of all 12 samples, but large variations were found for the individual samples. In particular the wavelength dependence was far from a constant ratio when plotted versus the surface spatial frequency. Hillocks on some of the aluminum films produced additional scattering. It was not possible to explain this additional scattering with the Twersky model of conducting hemispheres on an infinitely conducting plane.     

Light scattering and absorption by soot in the presence of sulfate aerosols

The radiative properties of aerosol-soot mixtures, both internal and external, are determined in the visible and near-infrared bands by use of exact indirect mode-matching solutions to electromagnetic-wave scattering from a sphere with an eccentric spherical inclusion and from a cluster of spheres. Spherical sulfate droplets are assumed to represent aerosol particles. Soot particles are represented by volume-equivalent carbon spheres, the size distribution of which is obtained from the number distribution of the primary carbon particles that aggregate into soot grains. The mean gram-specific absorption cross section and the mean albedo of aerosol-soot mixtures are obtained by integration of the corresponding characteristics of composite sulfate-carbon particles over the size range of carbon spheres. Enhanced absorption of light by soot in aerosol-soot mixtures, a result of lensing by sulfate droplets, is highlighted by maps of the electromagnetic field in a sulfate-carbon particle.     

Lidar differential absorption and scattering technique: theory

The results of theoretical investigations of the differential absorption technique for sounding atmospheric water vapor are described in this paper. The sources of errors and their effect on the results of interpreting the sounding data are analyzed. The mathematical problems for inverting the lidar returns are considered.     

Determination of the concentration of single-walled carbon nanotubes in aqueous dispersions using UV-visible absorption spectroscopy

Stable, homogeneous, aqueous dispersions of single-walled carbon nanotubes (SWNTs) are prepared by nonspecific physical adsorption of surfactants enhanced by sonication. Upon centrifugation, supernatant and precipitate phases are obtained. The initial weights of the SWNTs and the surfactant are divided between these two phases, and the respective SWNT concentration in each phase is unknown. The focus of this work is on the determination of the true concentration of raw, exfoliated HiPCO SWNTs in the supernatant phase. A UV-visible absorption-based approach is suggested for a direct measurement of the SWNT and the surfactant concentration in the supernatant. UV-visible absorbance spectra of SWNTs-surfactant dispersions and surfactants alone reveal that the intensity of a certain peak, attributed to the pi-plasmon resonance absorption, is unaffected by the presence of most surfactants. A calibration plot is then made by monitoring the intensity of the peak as a function of the true concentration of the exfoliated SWNTs. Thus, we are able to determine the unknown concentration of surfactant-dispersed HiPCO SWNTs in the supernatant solution, simply by measuring its optical absorbance. Moreover, we can now calculate the surfactant efficiency in dispersing SWNTs. Cryogenic-transmission electron microscopy and thermogravimetric analysis techniques are used for the characterization of these dispersions and to complement the UV-visible measurements.     

Optical properties of metal-dielectric multilayers in the near UV region

Metal-dielectric multilayers have versatile optical properties that can be used in many applications. The special properties of metal films in the near UV region are analyzed in terms of the d-band contribution to the plasma oscillation. The important parameters that determine the multilayer optical properties such as skin depth dependence on the wavelength and the thickness of silver films have been calculated. The morphology of silver films on titanium dioxide has been observed by TEM. The results indicate that an optimal thickness exists for near UV transparency, and that may be related to the resonance of voids and interface enhanced resonance-tunneling transmission of semi-continuous silver films. A special heat mirror with high transparency in the near UV region was designed and fabricated according to the optimal thickness of silver; it has been found to exhibit sound optical properties.     

Light scattering and absorption caused by bacterial activity in water

There is a growing class of elementary particle detectors, large-water ?erenkov detectors, that have a body of water (thousands of tons) as a sensitive medium. Particles are detected when they interact with the water and produce ?erenkov light, so detection efficiency relies on the transparency of the water. These detectors are active typically for many years, so biological activity (primarily bacterial growth) is one of the means by which the transparency of the water may be reduced. We present the results of a measurement of light scattering and absorption from a population of Escherichia coli in water, which is used as a model for bacteria in general. One can separate the scattering and absorption by varying the refractive index of the medium by using a solute of high molecular weight. We show that the results can be understood simply in terms of light scattering from small spheres (radius ≈ wavelength) with an effective refractive index, n(b), plus a small amount of absorption in the ultraviolet. We compare his scattering with Rayleigh scattering in pure water.     

Thermal diffusivity of carbon dioxide in the near critical region

An interference method for measurement of thermal diffusivity of transparent media is described. Values of the thermal diffusivity coefficient for carbon dioxide in the near critical region are obtained.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.27, No.3, pp.476–481, September, 1974.     

Nonequilibrium radiation of the shock wave in air in the vacuum ultraviolet region

A numerical model of generation of the nonequilibrium molecular radiation in a vacuum ultraviolet spectral region (VUV radiation with a wavelength shorter than 200 nm) behind a shock wave in air in a range of varying its velocity of 4.5–9.5 km/s is developed. This numerical model is verified using the results of experiments in a shock tube for studying the photoionization effect before the shock-wave front in a wave-length range of 85–105 nm. Some features of nonequilibrium VUV radiation, particularly its generation a very thin high-temperature layer behind the shock-wave front, are established.     

Measurement of the refractive index of distilled water from the near-infrared region to the ultraviolet region

By the minimum deviation method using a prism shaped cell, the absolute refractive indices of high-performance liquid chromatography distilled water were measured at the wavelengths from 1129 to 182 nm, at the temperature of 19 degrees C, 21.5 degrees C, and 24 degrees C, and then dn/dt at 21.5 degrees C was calculated. The coefficients of the four-term Sellmeier dispersion formula were determined by using the refractive indices at each temperature. As a result of the comparison of our refractive index data in the visible wavelength region with the formula by Tilton et al. at the National Bureau of Standards in 1938, both the refractive index data corresponded within 6 x 10(-6). In the UV region, the absolute refractive index at 193.39 nm calculated by the data measured nearby the wavelengths from 200 to 190 nm was 1.436517 (21.5 degrees C). The value was lower by 9 x 10(-5) or 10 x 10(-5) than the data measured by Burnett et al. at the National Institute of Standards and Technology.     

Resonant Raman and micro-Raman scattering from Si matrix with unburied beta-FeSi2 nanolayers

Samples, representing Si matrix with nanolayers of the semiconducting beta-FeSi2 silicide are studied by Raman scattering. The unpolarized Raman spectra of the samples are measured in two different configurations. It is found that the characteristic beta-FeSi2 Raman modes are seen in the spectra, taken at incident angle of about 45 degrees , while only comparatively intensive broad feature is detected in a back-scattering geometry. The difference in the spectra is interpreted with the appearance of surface polariton modes of the optical phonons in the nanosized layers in near back-scattering geometry. The resonant Raman scattering is investigated at incident light angle of about 45 degrees and the energies of the interband transitions in the investigated energy range are determined. It is known that the resonant Raman scattering appears to be even more precise method for the determination of the interband transitions energies than the modulation spectroscopy. Thus we claim that the energies determined here are firstly determined with such a precision.