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81.
Nonlinear optical properties of stimulated Brillouin scattering process in submerged object detection 总被引:2,自引:0,他引:2
Yuelan Lü 《中国光学快报(英文版)》2008,6(2)
Nonlinear optical properties of stimulated Brillouin scattering(SBS)to signal detection in water are analyzed.With the threshold characteristics,SBS only occnrs when the high power laser is focused in the SBS cell.When there is an object present in front of the focus,it leads to lower incident intensity and then SBS does not occur.The backward SBS signal depends on the focusing location.The nonlinear optical properties of SBS process in the focusing regime axe analyzed theoretically.With the object coming near to the focusing center,the backward Stokes signal rises up from zero to a maximum,and then grows to saturation.The delay time of the echo signal to pump signal can give the object location.In experiment,the peak position of varying rate of energy can give object location. 相似文献
82.
The paper presents construction and principle of operation of passive IR detectors (PIR detectors) of a large detection range.
Important virtue of these detectors is highly efficient detection of slowly moving or crawling people. The described here
PIR detector detects crawling people at the distance of 140 m. To ensure high probability of detection of slowly moving objects,
new method of signals analysis was applied. On the basis of the carried out real-time measurements, both probability of detection
and false alarms were determined. 相似文献
83.
The three-dimensional (3D) problem of the ground vibration isolation by an in-filled trench as a passive barrier is studied
theoretically. Integral equations governing Rayleigh wave scattering are derived based on the Green’s solution of Lamb problem.
The integral equations are solved accurately and efficiently with an iteration technique. They are used to evaluate the complicated
Rayleigh wave field generated by irregular scatterers embedded in an elastic half-space solid. The passive isolation effectiveness
of ground vibration by the in-filled trench for screening Rayleigh wave is further studied in detail. Effects of relevant
parameters on the effectiveness of vibration isolation are investigated and presented. The results show that a trench filled
with stiff backfill material gets a better isolation effect than a soft one, and increasing the depth or width of the in-filled
trench also improves its screening effectiveness. The effectiveness and the area of the screened zone are surging with the
increase in the length of the in-filled trench.
Supported by the National Natural Science Foundation of China (Grant Nos. 50678128 and 50538010) and the Research Fund for
PhD Student of Chinese College (Grant No. 20050247030) 相似文献
84.
Li Jingzhao Zhu Haiyong Zhenqiang Chen Zhang Ge Huang Chenghui Wei Yong Han Yongfei Chen Zhe Li Zhen 《Journal of Russian Laser Research》2008,29(3):288-295
We report a completely solid-state continuous-wave (CW) blue laser operating at 447 nm utilizing intracavity frequency tripling
of an LD-side-pumped Nd:YAlO3 (Nd:YAP) laser operating at 1341.4 nm. An LBO crystal with type-I critical phase matching and a KTP crystal with type-II
critical phase matching (CTM) were used for the second harmonic generation (SHG) and the third harmonic generation (THG),
respectively. In view of the analysis of the cavity stability, a four-mirror folded cavity was designed and the output characteristics
were theoretically analyzed. Experimental characteristics obtained were shown to be in agreement with the theoretical analysis.
The maximum output power of the 447 nm CW blue laser reached 114 mW, which corresponds to a red-to-blue conversion efficiency
of 9%. 相似文献
85.
86.
The continuous-wave laser properties of an efficient diode-pumped Nd:GdVO4 crystal operating at formed with a simple plane-concave cavity have been studied. With the incident pump power of 21 W, an output power of 6.9 W was obtained, giving an optical conversion efficiency of 32.8% and a slope efficiency of 35.3%. The laser characterization of two different Nd3+-doped concentration of Nd:GdVO4 crystals were studied. 相似文献
87.
LI Xinliang FU Dexun & MA Yanwen State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences Beijing China Correspondence should be addressed to Li Xinliang 《中国科学G辑(英文版)》2004,47(1):52-63
1IntroductionDirectnumericalsimulation(DNS)becomesanimportanttoolinrecentresearchofturbulence[1].DNSofcompressibleturbulenceismoredifficultthanthatoftheincompressibleturbulence.WhentheturbulentMachnumberisgreaterthan0.3theshockletsmayappearinthecompressibleturbulentflowfields.Thereasonandmechanismofshockletsexistencearenotclearyet.TheturbulentMachnumberinDNScannotbeveryhighwiththepresentexistingnumericalmethodsandcomputerresource.Fortheproblemofcompressibleisotropicturbulencewiththeinitia… 相似文献
88.
In beam injection flame furnace AAS (BIFF-AAS) the sample is introduced as a free-flying high-speed liquid beam into an AAS flame-heated nickel tube, resulting in a considerable improvement in the power of detection. For optimization of beam generation different nozzle types (smooth jet nozzles, turbulent working nozzles) have been compared at different pressures. It was found that the type of the nozzle hardly influences the analytical signal. However, the flow rates resulting from the different inner diameters of the nozzles and the applied pressures led to drastic changes in the analytical signal. For these investigations a recently developed 0.6 MPa (84 psig) diaphragm pump system was used. Furthermore, for the first time ever sub-critical liquid carbon dioxide has been used simultaneously as a liquid gas-pressure pump, as carrier in a flow-injection system (FIA), and for the beam generation. Transport of the carrier takes place as a result of the head pressure (6 MPa) of the liquid CO2 in the gas cylinder. For volatile elements (e.g. Cd, Hg, Pb, and Tl) detection limits between 0.2 µg L–1 (Cd) and 28 µg L–1 (Hg) were found, the standard deviation was from 0.6% to 3.2% depending on the element, concentration, and sample volume used. The use of liquid CO2 as a carrier in FIA systems opens up new possibilities for online sample pretreatment and trace preconcentration. 相似文献
89.
We consider two stochastic equations that describe the turbulent transfer of a passive scalar field (x)(t,x) and generalize the known Obukhov–Kraichnan model to the case of a possible compressibility and large-scale anisotropy. The pair correlation function of the field (x) is characterized by an infinite collection of anomalous indices, which have previously been found exactly using the zero-mode method. In the quantum field formulation, these indices are identified with the critical dimensions of an infinite family of tensor composite operators that are quadratic in the field (x), which allows obtaining exact values for the latter (the values not restricted to the -expansion) and then using them to find the corresponding renormalization constants. The identification of the correlation function indices with the composite-operator dimensions itself is supported by a direct calculation of the critical dimensions in the one-loop approximation. 相似文献
90.