Focusing on the underwater exploration potential of lidar and the limitations of physical limit on its detection sensitivity and detection accuracy, this paper focuses on modeling and analyzing the ultra-sensitive detection performance of entangled Fock state under seawater attenuation environment. Based on the LCMMS state, the entanglement detection model under seawater attenuation environment is established. The minimum phase error accuracy of LCMMS under the uniform distribution of photon number and the interference fringe contrast formula are derived. The simulation results show that the ultra-sensitive detection distance of the entangled Fock state under clear seawater can reach a distance of more than ten meters under water. The high photon number entangled state can make the distance higher; because LCMMS contains more high In the M and M' state of the photon number, the ultra-sensitive detection range of the quantum interferometric target detection of LCMMS under seawater loss is nearly 1.3 times that of the M and M' state.
The precise target identification is significant for commanding decisions and enemy identification. The micro-Doppler effect (MDE) can reflect the subtle movement characteristics of the target, which provides a new way for the target detection and recognition. However, the current research is mainly on the micro-motion feature extraction and classification of the targets, which is not capable for identifying the targets of the same type. This also reduced the application of the MDE. In fact, by accurately estimating the micro-motion parameters and combining sufficient prior knowledge, the target can be accurately identified. Further, the MDE detected by laser in infrared band has higher sensitivity and resolution than microwave detection, especially for the MDE generated by weak vibrations. Thus, in this paper, the photocurrent model of the laser detected MDE echo signal is established. The all-fiber coherent laser detection system for target micro-motion is designed. The detection sensitivity of and resolution requirements of the multicomponent micro-Doppler features are analyzed. Based on the time varying auto-regression (TVAR) model, the precise parameter estimation method for micro-motions are proposed, which provides the basis for target identification. The validity of the theoretical analysis and estimation method is verified through simulation. This research is helpful for extending the application of MDE from classification to precise identification in the future.
Coherent Doppler lidars (CDL) and coherent differential absorption lidars are widely applied in the measurements of atmospheric wind and constituents respectively. To improve the detection range of heterodyne lidars, the demands for laser linewidth are studied based on the statistical theory and Monte Carlo simulations. The signal to noise ratio (SNR) and the spectrum of intermediate frequency (IF) signal are analyzed under different laser power and linewidth. When the detection range is beyond the coherent length, the IF signal can still be measured, and the power spectrum of IF signal will be broadened, which results in the peak value decrease in the power spectrum. In heterodyne Doppler lidars, the frequency extraction errors of IF signal fluctuate with SNR. To realize the velocity measurement performance for wind and other moving targets, detection performances with various laser linewidth are analyzed according to the 3σ criterion. The calculations indicate that better results can be obtained with larger powers when the laser linewidth is relatively wider and that the effective detection range of lidar can be longer than the coherent length for lasers with certain linewidth. To verify the analysis, heterodyne experiments are carried out based on the fiber delay lines and fiber lasers with different linewidths, and the SNR is controlled by a variable optical attenuator. The results show that measurements with large laser power can reduce the errors caused by the power spectrum broadening of IF signal. The analysis may aid the determination of laser power and linewidth in heterodyne lidars.
In order to grasp the information of wind field and disturbance in the airport in real time, and to ensure the safety of flight, a method of detecting wind field disturbance using coherent laser is presented. A model to solve the vector velocity of the wind field disturbance is established in this paper. Based on the radial velocity simulation of coherent laser echo signal, a reliable and effective radial velocity data is provided for inversing the vector velocity of the wind field disturbance. Actually, the radial wind velocity appears relatively large fluctuations due to the distribution inhomogeneity of aerosol particles and sensor noise in actual measurement. Therefore, the purpose of adding random noise into the above-mentioned inversion of the radial wind velocity is to simulate the measured radial wind velocity data. In the case of noise interference, the damping least square algorithm is proposed to solve the numerical optimal vector velocity of the wind field disturbance to verify the solving model. In addition, the vector velocity of the wind field disturbance is compared and analyzed under different scanning azimuth interval. Through the simulation results, it shows that the mean square error(MSE) of inversion result is smaller with the decrease of scanning azimuth interval. When the scanning azimuth interval is less than 60°, the mean squared error of the vector velocity of the wind field disturbance is less than 1.14m/s, horizontal direction disturbance quantity is less than 4°, which lays a good theoretical basis for the follow-up field tests.
Spore is an important part of bioaerosols. The optical characteristics of spore is a crucial parameter for study on bioaerosols. The reflection within the waveband of 2.5 to15μm were measured by squash method. Based on the measured data, Complex refractive index of Aspergillus oryzae spores within the waveband of 3 to 5μm and 8 to 14 μm were calculated by using Krames-Kronig (K-K) relationship. Then,the mass extinction coefficient of Aspergillus oryzae spores within the waveband of 3 to 5μm and 8 to 14μm were obtained by utilizing Mie scattering theory, and the results were analyzed and discussed. The average mass extinction coefficient of Aspergillus oryzae spores is 0.51 m<sup>2</sup>/g in the range of 3 to 5μm，and 0.48m<sup>2</sup>/g in the range of 8 to 14μm. Compared with common inorganic compounds, Aspergillus oryzae spores possesses a good extinction performance in infrared band.
Quantum Sensors like Quantum Radar and Lidar based on the interference of non-classical states can achieve super-sensitivity beyond the Standard Quantum Limit (SQL). But as the photons transporting in atmosphere, the environmental interaction causes quantum de-coherence and results in the reduction of super-sensitivity range of the quantum sensors. The most significant effect of atmospheric transmission is photon loss along with phase fluctuation. In this letter, we introduce both the photon loss and phase fluctuation by adding a fictitious beam splitter in the signal arm of Mach- Zehnder interferometer (MZI). The density matrix with N00N and M&M' entangled states being the input states under the condition of photon loss and phase fluctuation is given respectively. Then as the optimal detection schemes parity operator is used as the detector and the formula of the sensitivity is derived. The super-sensitivity range of M&M’ and N00N states with de-coherence are simulated. As a consequence, with high photon loss M&M’ states shows the better phase sensitivity than N00N states but the N00N state is better when the loss is smaller than 20%. And with pure phase fluctuations N00N states get the longer range. M&M’ states is sensitive to the transmittance difference between two arms of the interferometer.