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Yang L.,University of Alabama in Huntsville | Nie J.,University of Alabama in Huntsville | Nie J.,State Key Laboratory of Pulsed Power Laser | Duan L.,University of Alabama in Huntsville
CLEO: QELS_Fundamental Science, CLEO:QELS FS 2013 | Year: 2013

We report the demonstration of a lidar based on optical sampling by cavity tuning. Target vibration as fast as 50 Hz has been successfully detected at an equivalent free-space distance of over 2 km. © 2013 Optical Society of America. Source

Dang K.-Z.,State Key Laboratory of Pulsed Power Laser | Dang K.-Z.,Electrical Engineering Institute | Shi J.-M.,State Key Laboratory of Pulsed Power Laser | Shi J.-M.,Electrical Engineering Institute | And 5 more authors.
Wuli Xuebao/Acta Physica Sinica | Year: 2015

High impedance surface, due to its unique property of in-phase reflection at some frequency, could be used in designing multiband Salisbury screen by replacing the metallic ground plane in a traditional structure, which is proposed, in this paper, to enhance the microwave absorbing performance of the conventional Salisbury screen. First, electromagnetic wave field intensity of different frequency in space after being reflected by a high impedance surface is analyzed, which implies that new absorption bands can be introduced at about the frequencies of in-phase reflection by sharing Salisbury screen's resistive sheet, without adding extra lossy materials such as lumped elements or others. Then, by taking a single band high impedance surface at 6.25 GHz and a dual-band high impedance surface at 6.27 and 8.17 GHz, which are both composed of patches array with varying periodic size and a thickness of 0.6 mm, the multiband Salisbury screens can be constructed utilizing a conventional one with an absorbing peak at about 10.5 GHz. The reflectivity of these multiband absorbers are simulated by employing the commercial CST microwave studio and later measured using a reflectivity measurement system comprising two polarized horns and a vector network analyzer. Experimental results agree well with the simulations, and all results verify that the method presented at the beginning is effective. Results also show that new additional absorptions appear at the frequencies where microwaves are nearly reflected in phase from the high impedance surface, with the same number of the in-phase reflection bands. Meanwhile, the original microwave absorbing capability of the traditional Salisbury screen is reserved mostly. Compared to the single band high impedance surface, the dual-band high impedance surface performs better in the design as the absorbing bandwidth is wider and the absorbing frequency is lower. With an additional thickness of the high impedance surface (no more than 1 mm), the total absorption bandwidth of the multiband Salisbury screen with a reflection below -10 dB increases from 8.5 to 10.1 GHz, and the lowest frequency with 10 dB absorption falls from 7.5 to 5.98 GHz. So it could be concluded that the design of multiband Salisbury screen is helpful to widen the absorption, especially towards the lower frequency direction. ©, 2015, Chinese Physical Society. All right reserved. Source

Wang E.,State Key Laboratory of Pulsed Power Laser | Wang E.,Key Laboratory of Electronic Restriction | Hu Y.,State Key Laboratory of Pulsed Power Laser | Hu Y.,Key Laboratory of Electronic Restriction | And 4 more authors.
Hongwai yu Jiguang Gongcheng/Infrared and Laser Engineering | Year: 2011

The influence of atmospheric attenuation and atmospheric turbulence on the detection performance of optical heterodyne detection ladar system should be analyzed in order to attenuate the effect of atmospheric turbulence. SNR, which is the key performance index of heterodyne system, was derived from the complex amplitude of light field and airy disk model on the detector surface. The influence of atmospheric attenuation and atmospheric turbulence on the complex amplitude of signal light field was analyzed, and the heterodyne detection efficiency affected by attenuation and phase vibration in weak turbulence was also analyzed. Numeric simulations show that atmospheric attenuation can't reduce the heterodyne detection efficiency, the main reason leading to lower SNR is the attenuation of return wave energy. The turbulence can cause phase vibration, amplitude vibration and transmitting direction fluctuation, and then make heterodyne detection efficiency reduce. Source

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