We present a landslide monitoring approach using a high-resolution distributed fiber stress sensor based on polarizationsensitive
optical frequency reflectometry (P-OFDR) technology. The sensing system consists of a polarizationmaintaining
(PM) fiber and an OFDR with a high spatial resolution. The PM fiber is used as a distributed sensing
element. The OFDR is used to measure the polarization mode coupling loss in PM fiber causing by the external pressure
along the PM fiber. With the advantages of frequency domain technique and coherent detection, the sensing system can
achieve high spatial resolution, high sensitivity and large dynamic range. By monitoring the mechanical property
distribution and variations in the landslide body, the occurrence of the landslides can be predicted accurately. We
demonstrate an early landslide warning system based on polarization-sensitive distributed fiber stress sensor, which has a
spatial resolution of 5cm, dynamic range of about 70dB and theoretical measuring range of 10km. The warning system is
also investigated experimentally in the field trial.
A robot scanning system consisting of a portable laser 3-D scanner and an industrial robot is demonstrated. In this system, the scanner is precalibrated by the traditional nonlinear two-step approach. In addition, by using a criterion sphere as the calibration object, a new robot tool center point (TCP) calibration approach is proposed for calibrating the relation between the precalibrated laser 3-D scanner and the robot. In this approach, two different translational motions of the robot are first made to determine the rotation part, and then at least three different rotational motions are made to determine the translation part. During the process, the extrinsic camera parameters are not recalibrated for each robot motion, so the calibration errors brought by camera calibration can be decreased. Moreover, the calibration error due to robot positioning error can be decreased by making use of the differences of different robot positions in calculations. An experiment was performed on a portable laser 3-D scanner and an ABB IRB-4400 industrial robot to test the validity of the proposed calibration approach. The experimental results show that this approach is simple and accurate compared to the conventional robot TCP calibration approach.
A red-sensitive acrylamide-based photopolymer based on multiple polymerizable monomers is developed in this paper for holographic applications. In order to improve the spatial resolution of this photopolymer system, a new strategy of employing low molecular-weight polyvinyl alcohol as binder is proposed. The comparative experiments of different photosensitive system with various molecular weights (72000,15000, 9000) are conducted to study their effects on the diffraction efficiency and spatial resolution. The experimental results show that the photosensitive system with low molecular weight of 9000 has much higher resolution and diffraction efficiency, and bright volume transmission grating with spatial frequency of 3000 lines/mm and diffraction efficiency higher than 85% can be recorded successfully on the optimum photopolymer material at the exposure level of 40 mJ/cm2. Some preliminary applications of spatial and angular multiplexing holographic storage for storing multiple binary and grey-tone optical images, are successfully demonstrated.
By employing new types of multi-color photosensitizers and photochemical promoters to photo-crosslinking gelatin system, a high-quality single-layer panchromatic dichromated gelatin material is achieved for color holography. Some preliminary results of spectral response, photosensitivity, and spectral selectivity are reported in this paper. Using red, green and blue lasers, namely three primary colors, the bright volume transmission and reflection holograms can be recorded successfully on the panchromatic material at the exposure level of 30 mJ/cm2. It can be expected to have practical applications in the fields of true-color display holography, wavelength multiplexing holographic storage, and holographic optical elements.
In this paper, a red-sensitive photopolymer based on multiple polymerizable monomers is developed for holographic applications. The detailed quantitative experiments on the reagent concentrations, the exposure, the thickness of the photosensitive layer, are conducted to determine an optimum recipe, and bright volume phase holograms with high diffraction efficiency are obtained in our experiments at the exposure level of 4mJ/cm2. This photopolymer also has higher resolution and self-development capacity. This makes it very convenient and useful for the applications of both real-time and double exposure holographic interferometry, some preliminary experiments of holographic interferometry are demonstrated in this paper for the nondestructive testing and measurement of minor distortion and displacement.
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