Piezoelectric ceramic transducers were made and embedded in concrete structures in this paper in order to monitor
cracks under static load. In the experiment, the component was made in concrete with rebars. The transducers were used
as sensors according to the direct piezoelectric effect and actuators according to the indirect piezoelectric effect. During
the experiment, sine pulse signals are applied on the transducer to generate elastic wave to scan the area between the
transducers. As being electronic device, signal of piezoelectric material will be disturbed by electromagnetic wave in
environment. Wavelet analysis with its good ability both in time and frequency domain was adopted in filtering the
interfering signal. Then damage index was established based on continuous wavelet analysis. From the change of the
damage index, the information of crack occurring and developing in the concrete component has been acquired. And the
trend of the damage index also has a good correlation with that of the strain gauges used in the experiment. The results
have shown that this method has the advantages that do not require sensors placed on the point of damage occurring and
can protect sensors from damage. Thus it can be used in the monitoring of civil structure.
Based on the multi-axial theory of stimulated Brillouin scattering (SBS), a group of coupled wave equations without limitation to the mode separation of a laser is deduced when the random initial phases of the axial modes are introduced for SBS pumped by a free operation laser. The coupling coefficient between two axial modes is obtained, and the dependences of the threshold and reflectivity of broadband SBS on the bandwidth, the mode number, the mode separation of the laser, are simulated numerically. The SBS threshold and reflectivity are dependent not only on the laser bandwidth, but also on the mode number and the mode separation of the laser.
Serial coherent laser beam combination is studied using one-dimensional transient model of stimulated Brillouin scattering (SBS). Beam combination is achieved by transferring the energy of several pump beams to one Stokes beam. The pulse-width of the Stokes beam, which is approximately equal to that of the pump, can be kept constant by adjusting the meeting position between Stokes beam and pump beams in the cell. Numerical simulation is made for the condition that power density of Stokes beam is larger than that of the pump beam. Simulation results show that the major factors that determine the energy extraction efficiency and the critical value of beam combination are the absorption of the medium and the length of SBS cell. The absorption loss is found to play a leading role, so that the overall energy extraction efficiency and the critical value of beam combination can be increased by using shorter SBS cells and/or medium with lower absorption rate. The simulation chooses CCl4 as target medium. The SBS cell length is 20cm; 20 beams (wavelength 1064nm, energy 1J, pulse-width 10ns, beam-area 1cm2) are combined in serial, one of which generates the Stokes seed, others are the pump beams. In order to keep the power density below 100MW/cm2 to avoid being more than threshold of SBS, the Stokes beams and pump beams must be expanded. The output beam of ~10J energy, ~10ns pulse-width, ~10cm2 beam area is obtained.
An experimental polarizing light source setup of high beam quality and variable-duration for KrF laser of the master- oscillator-power configuration, using stimulated Brillouin Scattering technique, is being built up. A design and experimental optimization for cavity type of the master oscillator utilizing an EMG101 KrF laser were made as a first step of the whole setup. The 1.23 m long oscillator cavity is formed by a 10 m rear concave full reflectivity mirror and flat quartz output coupler with selected reflectivity: 60%, 73%, 82% or 96%, and with choosing one of three intracavity aperture diameter: 1.1 mm, 1.5 mm and 2.0 mm, respectively. We have measured pulse energy and pulse width of the whole laser spot size output. The pulsewidth is 13.6 ns, 16.4 ns, 10.8 ns and 8.8 ns corresponding to reflectivity of front mirror 60%, 73%, 82% and 96%, respectively. We also measured seed beam outputs and seed beam divergences for the four kinds of reflectivity of front mirror and three kinds of iris diameter. As viewed from the sufficient polarizing output and sufficient high beam quality, the results for optimizing of oscillator cavity types is suitable reflectivity of front mirror of R <EQ 73% and suitable diameter of 1.5 mm with beam quality near 2.5X diffraction limited. The further steps of the building the whole above described experimental setup are undergoing.
A newly observed laser induced collision (LIC) and anti-stokes frequency up-conversion process in He/Ne mixture is reported. The fluorescence emission line of Ne at 486.7 nm can be enhanced 3 - 4 times by applying both discharge and optical excitation. The result shows that the LIC process can be a major competitive process in the two step excitation process. Both experimental description and theoretical analyses are given.
Radiation from two new kinds of rare-gas fluoride ionic excimers, Ar2+F- and Kr2+F- was observed near 125 nm and 148 nm in experiments. Detailed radiation processes and kinetics are analyzed theoretically and experimentally.
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