In-line Intensity Research Articles

Accurate Reference Gas Mixtures Containing Tritiated Molecules: Their Production and Raman-Based Analysis.

Highly accurate, quantitative analyses of mixtures of hydrogen isotopologues—both the stable species, H2, D2, and HD, and the radioactive species, T2, HT, and DT—are of great importance in fields as diverse as deuterium–tritium fusion, neutrino mass measurements using tritium β-decay, or for photonuclear experiments in which hydrogen–deuterium targets are used. In this publication we describe a production, handling, and analysis facility capable of fabricating well-defined gas samples, which may contain any of the stable and radioactive hydrogen isotopologues, with sub-percent accuracy for the relative species concentrations. The production is based on precise manometric gas mixing of H2, D2, and T2. The heteronuclear isotopologues HD, HT, and DT are generated via controlled, in-line catalytic reaction or by β-induced self-equilibration, respectively. The analysis was carried out using an in-line intensity- and wavelength-calibrated Raman spectroscopy system. This allows for continuous monitoring of the composition of the circulating gas during the self-equilibration or catalytic evolution phases. During all procedures, effects, such as exchange reactions with wall materials, were considered with care. Together with measurement statistics, these and other systematic effects were included in the determination of composition uncertainties of the generated reference gas samples. Measurement and calibration accuracy at the level of 1% was achieved.

Development of ionization chamber for in-line intensity monitoring of large profile parametric X-ray beam

An in-line ionization chamber has been developed for the real-time measurement of the absolute intensity of the pulsed parametric X-ray (PXR) beam during irradiation experiments. The quasi-monochromatic PXR generating system was developed at the Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University. In contrast to typical narrow X-ray beams in synchrotron radiation facilities, the PXR beam profile is as large as approximately 100 mm in diameter with rather uniform flux distribution at the X-ray output port in the experimental hall. The energy of the PXR beam ranges from 5 to 34 keV, which is specified by the PXR target crystal plane and its geometrical condition. The ionization chamber is of a plane parallel type employing 6-μm thick double-sided aluminum vapor-deposited polyester films for the plane electrodes through which the X-ray beam passes. The plane bias electrode has been placed at an equal distance of 25 mm from the two plane earth electrodes that act as the beam windows with an aperture diameter of 120 mm. Due to the pulsed property of the PXR beam and the geometrical configuration of the ionization chamber, the charge-sensitive preamplifier output pulse height represents an integral of the fast electron current, corresponding to a half of the total ionization charge produced by the beam. The intensity of the PXR beam has been measured for various X-ray energies by using nitrogen and argon, respectively, as the filling gas.

Plasmonic Variable Optical Attenuator Based on Liquid-Crystal Tunable Stripe Waveguides

A long-range surface plasmon polariton variable optical attenuator based on available nematic liquid crystals and polymers is proposed and theoretically investigated. It is demonstrated that the electro-optic control of the nematic molecular orientation is capable of tuning the level of index asymmetry of an Au stripe waveguide and the key properties of the fundamental long-range plasmonic mode, such as modal profile and propagation losses. By proper structural design and material selection, plasmonic in-line intensity modulators are designed, which exhibit very low power consumption, extinction ratios in excess of 30 dB, and insertion losses as low as 1 dB for a device length in the millimeter range. Such active plasmonic elements are envisaged to be used in interchip photonics bus interconnects.

Strain Engineering of Plasma Dispersion Effect for SiGe Optical Modulators

The plasma dispersion effect and free-carrier absorption in strained SiGe are analyzed using the six-band k· <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</i> method and the Drude model. Since the hole conductivity mass of SiGe is decreased by applying compressive strain, enhancement of the plasma dispersion effect, and free-carrier absorption in strained SiGe is expected. We predict that Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> coherently grown on Si will exhibit three times higher plasma dispersion and four times higher free-carrier absorption than Si. The modulation characteristics of SiGe quantum well metal-oxide-semiconductor (MOS) optical modulators are also analyzed by technology computer-aided design simulation and finite-difference optical mode analysis. An extremely small V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> L of 0.033 V-cm is predicted in the case of a compressively strained Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> quantum well in conjunction with a high-k gate dielectric MOS structure. The enhancement of free-carrier absorption in the SiGe high-k MOS modulator also makes in-line intensity modulation feasible and an intensity modulation efficiency of 9 dB/mm/V is predicted.

Statistically principled use of in-line measurements in intensity diffraction tomography

Intensity diffraction tomography (I-DT) reconstruction theory provides a mathematical mapping between two in-line intensity measurements acquired at a given tomographic view angle and Fourier components of the object function. Poles in this mapping will cause certain Fourier components to contain greatly amplified noise levels when applied to noisy measurement data, which can result in noisy and distorted images in practice. We investigate the statistically principled use of multiple in-line intensity measurements in I-DT. Reconstruction methods are developed that exploit the statistical structure of the in-line measurements to minimize the variance of the estimated Fourier components of the object function.

Waveguide fabrication and high-speed in-line intensity modulation in 4-N,N-4′-dimethylamino-4′-N′-methyl-stilbazolium tosylate

We report the formation of thin-film waveguides of organic crystals by precision optical polishing and the fabrication of an electro-optic intensity modulation device based on a thin-film waveguide of N,N-4′-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST®) as an overlay on a side-polished fiber (SPF). Successful fabrication of single-crystal DAST® waveguides with thicknesses in the 20–25 μm range have been produced. The waveguides were investigated via an evanescent coupling technique using side-polished fibers rather than traditional end-firing methods. Surface quality is believed to have been sufficient for low-loss propagation. Electrodes were added to the SPF/DAST® overlay architecture and intensity modulation observed out to 18 GHz. The device frequency response is believed to extend beyond 100 GHz under optimum conditions.

Fibre optic modulators using active multimode waveguide overlays

The evanescent field coupling between a singlemode optical fibre, side polished dose to the core and a high index, multimode, planar waveguide overlay has been investigated as a means of realising inline modulators without interruption of the fibre. Oils of known refractive index and thin layers of polished lithium niobate have been used in the role of the overlay and an electron-optic inline intensity modulator based on the latter has been realised and tested. The results demonstrate the technical feasbility of fabricating rugged, low loss solid state devices offering performances which are realistic in terms of applications.