We have developed a novel method of wavelength division multiplexed operation of thermally stabilized fiber Bragg grating (FBG) vibration sensors in that simultaneous multipoint vibration detection with a temperature-insensitive operation can be achieved. One of the sensing elements of the arrayed sensors consists of a pair of FBGs, one is used for providing a narrowspectrum light from a broad-spectrum incoherent optical source and the other is used for vibration sensing. The paired FBG configuration enables us to compensate the temperature effects that are commonly applied to the FBGs used. In the experiment, two sensing elements are arranged in tandem and the detection of simultaneous two-point multiple vibrations and the measurement of an elastic wave propagating in a metal bar are demonstrated.
The production of point X-ray sources for hard X-rays of approximately 8 keV is proposed and their application to Gabor holography is examined. Small X-ray sources less than 100 nm in diameter are obtained by total reflection from a limited surface area at grazing incidence. A microstrip plated with heavy metal on a glass plate is used for a one-dimensional small X-ray source and crossed glass rods for a two-dimensional X-ray source. A virtual source width smaller than approximately 80 nm is demonstrated. Young's X-ray interference fringes are obtained using beams reflected from two microstrips. Gabor X-ray holograms of a gold wire and a diatom are recorded with a virtual point source and their reconstructed images are numerically obtained.
A Zernike-type phase-contrast X-ray microscope with a zone plate and a phase plate was constructed at the Photon Factory BL3C2. Parallel monochromatic X-rays of 8.97 keV were incident on a specimen and a direct beam transmitted through the specimen was focused on the back focal plane of the zone plate, where an aluminium phase plate was placed. Tantalum line patterns as fine as 0.3 microm could be imaged. Phase-contrast images of polypropylene wires and polystyrene latex beads were obtained, which showed better contrast than that of their bright field images.
A wavelength-switchable and tunable fiber ring laser has been proposed to implement an optical source of a fiber Bragg grating (FBG) vibration sensor array based on intensity modulation technique. The laser consists of an erbium-doped fiber amplifier (EDFA) and an optical switch with tuning FBGs, in which the lasing output is coupled out from a selected tuning FBG and serves as an optical source of one of the multiplexed FBG vibration sensor elements. By changing the channel of the optical switch, the lasing wavelength can be chosen for the sensing FBG of the respective sensor element. In addition, the temperature effects on the sensor outputs due to environmental temperature can be eliminated when the temperature changes are applied commonly to both the tuning and sensing FBGs. In the experiment, multipoint vibration detection with a temperature-insensitive operation is successfully demonstrated by constructing two sensor elements arranged in parallel.
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