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2 May 2005

Volume 86, Issue 18, Articles (18xxxx)

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Appl. Phys. Lett. 86, 181101 (2005); http://dx.doi.org/10.1063/1.1920407 (3 pages)

Giacomo Scalari, Nicolas Hoyler, Marcella Giovannini, and Jérôme Faist
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Microfluidic detection and analysis by integration of thermocapillary actuation with a thin-film optical waveguide

Joseph P. Valentino, Sandra M. Troian, and Sigurd Wagner

Appl. Phys. Lett. 86, 184101 (2005); http://dx.doi.org/10.1063/1.1922075 (3 pages) | Cited 11 times

Online Publication Date: 25 April 2005

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We demonstrate a nonintrusive optical method for microfluidic detection and analysis based on evanescent wave sensing. The device consists of a planar thin-film waveguide integrated with a microfluidic chip for directed surface flow. Microliter droplets are electronically transported and positioned over the waveguide surface by thermocapillary actuation. The attenuated intensity of propagating modes is used to detect droplet location, to monitor dye concentration in aqueous solutions, and to measure reaction rates with increasing surface temperature for a chromogenic biochemical assay. This study illustrates a few of the capabilities possible by direct integration of optical sensing with surface-directed fluidic devices.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
47.85.Np Fluidics

Temporal correlation scheme for spectroscopic gas analysis using multimode diode lasers

G. Somesfalean, M. Sjöholm, L. Persson, H. Gao, T. Svensson, and S. Svanberg

Appl. Phys. Lett. 86, 184102 (2005); http://dx.doi.org/10.1063/1.1921351 (3 pages) | Cited 12 times

Online Publication Date: 26 April 2005

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The reliability of diode lasers used in spectroscopic applications is limited by their intrinsic multimode and mode-jump behavior when wavelength-tuned by current or temperature. We report on a scheme for gas analysis based on temporal correlation between absorption signals from an unknown external and a known reference gas concentration, simultaneously recorded when the diode laser wavelength is temperature-tuned across absorption features of the gas of interest. This procedure, which does not require any knowledge of the exact spectrum, also eliminates light intensity fluctuations due to mode competition. The method is illustrated for atmospheric oxygen absorption applied to diffusion measurements.
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42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
82.80.-d Chemical analysis and related physical methods of analysis
42.55.Px Semiconductor lasers; laser diodes
93.85.-q Instruments and techniques for geophysical research: Exploration geophysics

Low angular-dispersion microwave absorption of a metal dual-period nondiffracting hexagonal grating

Matthew J. Lockyear, Alastair P. Hibbins, J. Roy Sambles, and Christopher R. Lawrence

Appl. Phys. Lett. 86, 184103 (2005); http://dx.doi.org/10.1063/1.1921345 (3 pages) | Cited 5 times

Online Publication Date: 26 April 2005

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The microwave (11.3<λ0<16.7 mm) reflectivity response of a nondiffracting dual-period hexagonal grating is explored. In three directions at 60° to each other, the aluminum grating has a repeat period of 7.2 mm in which are three equally spaced grooves, one being slightly shallower than the other two. This dual-period (λg and λg/3) structure exhibits strong microwave absorption at several different frequencies. In addition, some of the absorptions are almost completely independent of the angle of incidence and polarization of the microwave radiation.
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78.70.Gq Microwave and radio-frequency interactions

Stationary scanning x-ray source based on carbon nanotube field emitters

J. Zhang, G. Yang, Y. Cheng, B. Gao, Q. Qiu, Y. Z. Lee, J. P. Lu, and O. Zhou

Appl. Phys. Lett. 86, 184104 (2005); http://dx.doi.org/10.1063/1.1923750 (3 pages) | Cited 49 times

Online Publication Date: 29 April 2005

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We report a field emission x-ray source that can generate a scanning x-ray beam to image an object from multiple projection angles without mechanical motion. The key component of the device is a gated carbon nanotube field emission cathode with an array of electron emitting pixels that are individually addressable via a metal–oxide–semiconductor field effect transistor-based electronic circuit. The characteristics of this x-ray source are measured and its imaging capability is demonstrated. The device can potentially lead to a fast data acquisition rate for laminography and tomosynthesis with a simplified experimental setup.
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07.85.-m X- and γ-ray instruments
85.35.Kt Nanotube devices
79.70.+q Field emission, ionization, evaporation, and desorption
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