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It is undeniable that more and more simple and rapid techniques are necessary to satisfy the increasing need of the gas detection in unconventional natural gas industry. Terahertz (THz) technique, a recently developed spectral method, was used to realize the identification and determination of the principal gas components distilled from oil shale, including methane (CH 4 ), ethane (C 2 H 6 ), carbon monoxide (CO) and carbon dioxide (CO 2 ). An obvious variation can be observed between the components after the measurement of THz. C 2 H 6 represented the largest refraction property because of the highest time delay relative to the reference, followed by CO 2 , CH 4 and CO in turn. In addition, back propagation artificial neural network was employed to quantitatively characterize the components’ content and the total pressure of the four-component system. The correlation coefficient of the prediction set in the quantitative model equalled 0.9955. The results indicated that THz technique combined with mathematical method is an effective tool for gas detection and can be popularized in unconventional natural gas industry.

Optical assessment of oil shale using terahertz time-domain spectroscopy (THz-TDS) was carried out to study oil potential. Fischer assay testing was employed to obtain the oil yield of oil shale specimens to examine the difference of oil potential between oil shale samples from three regions: Beipiao, Barkol, and Huadian in China. Then, two types of specimens from each area were prepared for the optical tests and the results were compared. The refractive index (n) at 0.2–1.2 THz was derived; n decreased slowly with increasing frequency for all the specimens despite the oscillation pattern observed at lower frequencies. The specimen preparation method that mixed the powdered material led to minor differences between the specimens. The different response of kerogen to the terahertz pulse depending on the kerogen's evolutionary stage leads to a difference in the refractive index between the specimens from the various regions. This study indicates that using THz-TDS to evaluate the oil content in oil shale without inducing reaction within the specimen can be an effective method for resource exploration.

The application of terahertz (THz) technique in many fields like petroleum industry requires the high resolution and multifunction to realize the precise detection of different materials. In this study water vapor in atmosphere was scanned with shortand long-path THz spectrometers with different scan ranges. The full width at half maximum of the THz characteristic lines in long-path system reached less than 7 GHz and that in short achieved ∼5.5 GHz, indicating that the THz spectroscopy of water vapor can be used to calibrate THz devices. THz systems with right scan ranges could be a promising selection for the identification of solid, liquid and gaseous materials with very similar structures due to the high resolution. The research demonstrates that the multifunctional THz test can be realized through the balance of resolution and sampling space in many fields, such as oil-gas industry.

Interfacial microstructure tunable photovoltaic effects have been reported in heterojunctions of La(1-x)Ca(x)MnO(3) thin films and tilted or exact cut Nb-doped SrTiO(3) single crystal substrates under irradiation of UV pulsed laser. The photoresponse times of vicinal junctions and films were obviously faster than those of exact cut samples. The behaviors can be explained by the slope of the built-in electric field in the 10° tilted heterojunction and the interfacial terrace microstructure of La(1-x)Ca(x)MnO(3) films.

Heptafluoropropane (HFP), as the best alternative to halon fire-suppression agents, is now a widely used fire extinguishing agent. The current studies of HFP, concentrating on the extinguishing mechanisms of flames and decomposition products, in general deal with the destructive and high temperature cases. In this paper, terahertz time-domain spectra are used to characterize HFP at different pressures. Optical parameters of HFP, such as absorption coefficient, refractive index, and relative permittivity, and their relationship with concentration of samples, are discussed. The absorption peak of HFP at 0.3 THz depends strongly on the applied pressure, and the corresponding parameters increase almost linearly with increasing HFP concentration. The present study lays a foundation for future extensive applications.

Micrometer-thick perovskite-type multilayer heterostructures with ten thousands of unit cells, [SrNb(0.05)Ti(0.95)O(3)/La(0.9)Sr(0.1)MnO(3)](3), have been fabricated on Si substrates. The structure exhibited nonlinear and rectifying current-voltage characteristics. Stable and temporal photovoltaic effects in the multilayer have been experimentally studied by using different wavelength light sources from ultraviolet to infrared, respectively. The photovoltage and photocurrent responsivities as a function of wavelength displayed that two cutoff wavelengths occurred corresponding to the band gaps of SrNb(0.05)Ti(0.95)O(3) and Si and La(0.9)Sr(0.1)MnO(3). Under the pulsed laser illumination the nanosecond response characterization of the present multilayer structure was obtained. Based on the band structure of the multilayers, a possible mechanism of photovoltaic process was proposed. c 2008 American Institute of Physics. [DOI: 10.1063/1.3010373]

We have fabricated a three-component perovskite-type superlattice (SL) consisting of La(0.9)Sr(0.1)MnO(3), SrTiO(3) and LaAlO(3) with atomic scale control by laser molecular beam epitaxy on Si substrates. When a He-Ne laser irradiated the superlattice by side illumination, a stable photovoltage was produced and the responsivity reached 46.7 mV mW(-1) which is six times higher than that of a similarly grown La(0.9)Sr(0.1)MnO(3) single layer on Si substrates. This work demonstrates the potential of the present SL in photo-detectors operating at room temperature.