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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9201-9205 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We develop a method for measuring absolute two-photon absorption cross sections (σ2) and employ it to determine the σ2 of Rhodamine-6G in methanol (16.2±2.4 GM at 806 nm). Our measurement calibrates the relative excitation spectrum previously reported for this chromophore. The method is based on our derivation of an analytical expression describing the transmission of Gaussian laser pulses through a two-photon absorbing medium. The expression is valid for arbitrary absorber thickness, at all distances from the focus. This generalizes the prevalent "z-scan" (translation of the sample along the beam direction) technique for measuring two-photon absorbance, removing the requirements of a "thin" (thickness (very-much-less-than) Rayleigh range of the focused laser beam) sample and of placing the sample at the focus. This leads to an improvement of the sensitivity of the technique by over two orders of magnitude, enabling measurement of the two-photon absorption cross sections of even weakly absorbing specimens at moderate intensities. The results are significant for applications such as nonlinear microscopy, optical data storage and optical power limiting. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 4670-4673 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A vacuum gauge has been designed and fabricated using a new type of sensor element, the semiconducting barium titanate positive temperature coefficient (PTC) thermistor. It covers a much wider range and better resolution compared to conventional Pirani gauge and other thermistor vacuum gauges particularly in the low vacuum levels due to its extreme high temperature coefficient. The details of design criteria of the instrument and its performance characteristics have been discussed. Due to the unique autocurrent limiting and stabilizing capabilities of a PTC thermistor, the fabrication of the instrument appears to be much cheaper. © 2000 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 2792-2795 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Moisture sensors based on porous alumina were designed and fabricated to detect and measure the concentration of moisture in gases. In the thin alumina disks taken, the surface and penetration effect has been considered during the process of adsorption and absorption of water molecules through pores and grain boundaries. Three different fabrication techniques, the tape casting technique, pelletization, and porous thick film, have been tried to achieve the desired moisture-sensing property of the samples. Different types of electrode structures and designs were also investigated and optimized to obtain maximum sensitivity. Electrodes were formed by screen printing the samples with thick film conductive pastes. The planar porous alumina sensor so obtained is found to be sensitive in the range of the 100–1000 ppmv level of moisture. The response time of the sensor in the ppmv range is approximately 2 min, and at higher concentrations of moisture it shows quasilinear dependency on the moisture content. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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