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A tunable single frequency laser with ultralow-noise and high vibration resistance is developed,and its working principle and structure design are introduced.The laser worked at 1 550 nm is consisted of a single frequency laser resonant cavity,a polarization containing optical fiber amplifier and a monitoring feedback optical path.By using a closed-loop temperature control technology,the laser shows a higher precision and stability,and its extremely temperature control resolution is up to 0.001 ℃.Using frequency components and a matched closed-loop system,the locked output frequency and power of the laser are implemented.The closed loop system not only gives the stability of wavelength and power,but also greatly reduces the low frequency noise of the laser system and effectively improves the laser damage threshold.As a result,the fiber laser can provide the long-term power stability better than 1% and the relative intensity noise better than-130 dBc/Hz.By selecting different types of seed light source cavities,the laser line-width can be controlled in the 1-400 kHz.Furthermore,the output power of fiber laser is 1 W and tunable wavelength is 3 nm.At 1 Hz,the phase noise is less than 10 μrad·Hz-1 2/m OPD and the shock resistance ability is 0.1g(g for the acceleration of gravity).

The influence of reinforced bar corrosion on the bond degradation in lightweight concrete was studied. Accelerated constant current corrosion tests were performed on lightweight reinforced concrete samples, and the influential factors, such as protective layer thickness, reinforced bar diameter and corrosive level were investigated. The constant current step method was used to measure the electric resistance of the concrete protective cover, which was used to characterize the corrosion level of the rebar. Experimental results indicated that the corrosive resistance increased with increasing the cover dimension and decreasing the reinforced bar diameter, and the rate of decrease in the specimen impedance after cracking depended on the cover dimension. A new medium was offered for the further research on the performance degradation of corrosion lightweight concrete.