共查询到20条相似文献,搜索用时 15 毫秒
1.
A bi-directional laser Doppler velocimeter utilizing optical frequency shifting has been developed. Optical frequency shifting is achieved by using a rotating radial grating. A high diffraction efficiency permits the system to be used in the fringe mode. The zero velocity frequency shift can be varied from 0.1 to 2.5 MHz with a stability better than 0.2%. Important applications are velocity measurements in reversing flows, highly turbulent flows, two-phase flows, and boundary layers. The system described may also be used for vibration analysis. Experimental results are presented. 相似文献
2.
A mobile molecular Doppler wind lidar at an eye-safe wavelength of 355 nm based on double-edge technique is being built in Hefei (China) for wind measurement from 10-to 40-km altitude. The structure of this lidar system is described. A triple Fabry-Perot etalon is employed as a frequency discriminator whose parameters are optimized. The receiver system is designed to achieve compactness and stability by putting in a standard 19-inch socket bench. Simulation results show that within the wind speed dynamic range of ±100 m/s, the horizontal wind errors due to noise are less than 1 m/s bdow 20-km altitude for 100-m vertical resolution, and less than 5.5 m/s from 20 km up to 40 km for 500-m vertical resolution with 400-mJ laser energy, 30-min temporal resolution, and a 45-cm aperture telescooe. 相似文献
3.
In order to improve the resolution of seismic acquisition, a new seismic acquisition system based on tangential laser Doppler effect with an optimized differential optical configuration is proposed. The relative movement of the inertia object and the immobile frame is measured by laser Doppler effect, which can avoid the electromagnetic and thermometric interference, and the adoption of frequency-modulated (FM)transmission can improve the ability of anti-jamming. The frequency bandwidth is properly determined by analyzing the frequency of the Doppler signal. The velocity, displacement, acceleration, and frequency to be measured can be real-time acquired by frequency/velocity (F/V) converting the FM Doppler signal.A 100-dB dynamic range and the linear frequency range of 1.0 to 1000 Hz are realized. 相似文献
4.
The master laser of an injection-seeded laser for Doppler wind lidar is frequency stabilized to a FabryPerot (FP) cavity using Pound-Drever-Hall technique. The FP cavity is specially designed to gain high temperature stability with Zerodur cavity and spacer. A computer based controller is used to sample and process the error signal. After the master laser is locked, the relative frequency drift is±25 kHz in 1 s,and ±55 kHz in 1 h, which can satisfy the need of Doppler wind lidar. 相似文献
5.
An idea of using laser Doppler velocimeter (LDV) to measure the velocity for the vehicle inertial navigation system was put forward. The principle of measuring its own velocity with laser Doppler technique was elaborated and reference-beam LDV was designed. Then Doppler signal was processed by tracking filter, frequency spectrum refinement and frequency spectrum correction algorithm. The result of theory and experiment showed that the reference-beam LDV solved the problem that dual-beam LDV cannot be used for measuring when the system was out of focus. Doppler signal was tracked so that signal-to-noise ratio was improved, and the accuracy of the system was enhanced by the technology of frequency spectrum refinement and correction. The measurement mean error was less than 1.5% in velocity range of 0-30 m/s. 相似文献
6.
研究了利用运动光栅的多普勒效应进行切向位移的遥测技术。提出了测量光路,采用声光调制器作为分光和频移器件并用于鉴向,实现了50m的远距离光栅位移遥测。达到测量分辨率0.8μm,光栅位移40mm,最大累积误差优于34μm。并用理论分析和实验,证明了远距离目标的焦深及其计算方法,导出了计算公式。 相似文献
7.
A direct detection Doppler wind lidar with the dual Fabry–Perot technique has been built in Hefei, China, and the system is
described in this paper. A dual, air-spaced Fabry–Perot etalon is designed as the frequency discriminator and the transmission
characteristics are measured with a stabilized cw laser and a pulse laser. The experimental data are found to be in agreement
with the designed parameters. The Doppler shift is measured by taking the ratio of the transmitted intensities from the dual
etalon. Analysis of the accuracy of Doppler measurement is made by considering the factors of the number of iterations in
converting the measured ratio to the Doppler shift, the laser intensity fluctuation and the signal-to-noise ratio. In the
sufficient signal-to-noise ratio the velocity accuracy of the Doppler lidar system is estimated to be better than 0.5 m/s. 相似文献
8.
A. V. Kozlovskii 《Journal of Experimental and Theoretical Physics》2001,93(3):462-470
The interaction of a two-level atom uniformly moving along a classical trajectory with a high-Q cavity quantum mode is analyzed. The dressed-state method is used to derive a recurrence formula for the transition probability of the atom with photon emission; the temporal dynamics of this probability qualitatively depends on the Doppler shift of the atomic transition frequency, on the Rabi frequency of the atom-field system, and on the detuning of the atomic transition frequency from the field mode frequency. The emission dynamics of a moving atom is very sensitive to the detuning. Rabi-type oscillations with a frequency equal to the Doppler shift can arise under certain conditions. At resonance, the emission probability of a moving atom can considerably exceed the emission probability of an atom at rest. A plane-parallel-mirror cavity and a confocal spherical-mirror cavity are considered. It is shown that the peculiarities of Doppler-Rabi oscillations must be taken into account in micromaser theory. 相似文献
9.
We here developed and evaluated a laser frequency control system which synchronizes the laser frequency to the resonance of target Ca + isotope ion whose having more than 8 GHz of isotope shift based on the Fringe Offset Lock method for simple operation of ICPMS-ILECS (Inductively Coupled Plasma Mass Spectrometry - Ion trap Laser Cooling Spectroscopy) The system fulfilled the minimum requirements of four slave lasers stability for Doppler cooling of Ca + ions. A performance of the system was evaluated by cooling 40Ca + ions with the stabilized slave lasers. All the stable even Ca + isotope ions were trapped and their fluorescence was observed by switching laser frequencies using the system. An odd calcium isotope 43Ca +cooling was also succeeded by the control system. 相似文献
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11.
The single longitudinal mode operation and frequency stability are essential for the laser transmitter used in the Doppler lidar. We devise a seed injection, frequency tunable and locked Q-switched Nd:YAG laser for the direct detection Doppler lidar. By implementation of the dual-wavelength seed laser and iodine-based PID frequency-locking technique, the frequency-stabilized seed laser is robust to interference and can be locked within 200 kHz for 3 h. The stable output of single longitudinal mode of the frequency-doubled pulsed laser makes it possible to achieve operational wind measurement. 相似文献
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14.
使用单个传感器实现水下航行器纵向分布噪声源位置的估计。应用传感器接收的多普勒信号瞬时频率变化率具有极值性的特点,通过推导并定义一种时间-频率变化率分布(L-相位分布),给出其有效离散迭代算法,能够提取出多普勒信号的瞬时频率变化率曲线,得到该曲线极值点位置的估计值,并结合水下航行器的航速,可以估计出线谱噪声源在航行器上纵向的分布位置。海试数据给出了105 Hz,220 Hz和500 Hz等三种线谱噪声源的位置估计误差,其定位误差均不超过2.5 m,表明该方法对于中低频率噪声源具有较高的位置估计精度。 相似文献
15.
Previous dual-frequency lasers mainly made use of artificial birefringence for frequency splitting, which were of a limited-frequency difference stability and complex construction. In this paper, we invented a novel Zeeman-birefringence He-Ne dual-frequency laser without any artificial devices, but by hole drilling in the cavity mirror. The laser-frequency difference (LFD) ranging from kilohertz to tens of megahertz was realized and the relationship between the LFD and the hole geometric sizes was investigated. Theoretical analyses were carried out. Characteristics of the LFD were explored for both the indium-sealed and hard-sealed lasers with a frequency stabilization system. The results showed the LFD with hole-drilling, indium-sealed lasers is maintained at 30 kHz within 2 h, which is better than the hard-sealed ones with a stability of 200 kHz within 2 h. The hole-drilling Zeeman-birefringence He-Ne lasers may make significant progress for the light source of the interferometers and Doppler velocimeters. 相似文献
16.
Y. D. Peng Z. J. Zhang X. Q. Wang S. D. Liu A. H. Yang X. S. Wang 《Optical and Quantum Electronics》2018,50(8):311
A scheme of electric-field measurement of micro-waves is proposed in Rydberg atoms with Doppler effects. A cascade-type electromagnetically-induced-transparency (EIT) system is disturbed by a perturbative field coupling a metastable transition. The original dark state splits and two EIT window appear with a central absorption peak. When a micro-wave (MW) field couples the Rydberg transition, the central absorption peak is divided into two. The frequency splitting of two central peaks is proportional to the MW field intensity, which can be used to probe MW electric field strength. This frequency-readout method based on a double-dark state system increases the probe sensitivity nearly by a factor of 7, compared with that of the single-dark state case. At room temperature, Doppler effects can enhance the absorption spectrum, moreover, its peak value varies linearly with the MW field strength. This can also serve to measure MW electric field strength. Numerical results show that the latter intensity-readout method after Doppler averaging improves the probe sensitivity by a factor of 10 with respect to the case without Doppler effects. 相似文献
17.
This is a brief discourse on the history of the uses of acoustic Doppler frequency shifts in modern medicine. The Doppler effect and the Doppler equation are discussed. The technological developments over the last half century are covered, as well as their applications in diagnostic medical sonography. A limited discussion of the pathologies that may be diagnosed using the Doppler effect is also presented. 相似文献
18.
Comparison between effects of Doppler broadening on pure and non-pure inversionless gains with frequency up-conversion
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A study is made of the effects of Doppler broadening on
pure gain without inversion, which means that neither one-photon
nor two-photon inversions are allowed, and non-pure gain without
inversion, which means that one-photon inversion does not occur
but two-photon inversion is present, in a closed Λ-type
three-level system with incoherent pumping. It is shown that when
the driving field is resonant but the probe field is not, in a
certain range of Doppler width, for the case of the lower degree of
frequency up-conversion, generally, pure gain without inversion
increases monotonically and non-pure gain without inversion does
not monotonically increase or decrease with increasing Doppler width;
for the case of the higher degree of frequency
up-conversion, pure gain without inversion decreases
monotonically but non-pure gain without inversion cannot be
produced. In the case of two-photon resonance, in some range of
Doppler width, pure gain without inversion does not
monotonically increase or decrease while non-pure gain without
inversion decreases monotonically with Doppler width increasing.
Finally, an experimental scheme for examining our theoretical result
is given. 相似文献
19.
Experimental study of the effects of pulsed Doppler sample volume size and position on the Doppler spectrum 总被引:1,自引:0,他引:1
With a pulsed Doppler system, the recorded Doppler spectrum is expected to vary depending upon the sample volume size relative to the diameter of the vessel, the position of the sample volume in the vessel and the velocity profile. In the in vitro experiments described in this paper, the velocity profile was kept constant by using steady parabolic flow in a flow model. As the Doppler sample volume size and position were changed, the maximum variations of quantitative measurements from the Doppler spectrum were determined. The maximum, mean and mode frequencies and spectral broadening index (SBI) were affected by the position of the sample volume but to a lesser degree by its length (1.5-5.0 mm) relative to the 9.5 mm beam path length across the tube. When the centre of the Doppler sample volume was moved within the central 25% of the tube, the maximum variations were as follows: maximum frequency 3-5%, mean frequency 8-9%, mode frequency 8-9% and SBI 16-18%, where the range indicates the effect of increasing the sample volume size. Based on these results obtained under steady flow conditions in vitro, it is concluded that quantification of pulsed Doppler spectra may be feasible if the sample volume is positioned within the central 25% of the vessel. 相似文献