Study On The Echo Characteristics Of Dual-wavelength Alternating Pulse Laser Transmission In The Atmosphere

Compared with single-wavelength laser,dual-wavelength laser has a wider application in the fields of laser ranging and laser communication.At present,the accuracy of dual-wavelength laser measuring and detecting devices can reach centimeter or even millimeter level.However,due to the existence of atmospheric turbulence,the atmospheric refractive index changes dramatically.Phase distortion and waveform distortion caused by laser in the process of spatial transmission can seriously damage the quality of the signal,which reduces the accuracy and reliability of laser ranging.Therefore,the influence of atmospheric turbulence on the process of dual-wavelength laser transmission cannot be ignored.Currently,the research on laser atmospheric transmission mainly focuses on the theoretical and experimental study of single-wavelength laser atmospheric transmission characteristics,including light intensity flicker,pulse broadening,spot drift,angle of arrival fluctuation,and so on.The propagation characteristics of dual-wavelength laser in atmospheric environment have not been reported yet.Therefore,there is no theoretical basis to improve the accuracy of dual-wavelength laser measurement and detection devices by studying the effect of turbulence on the dual-wavelength laser echo signal.In this paper,the echo characteristics of two-wavelength alternating pulse laser transmission in the atmosphere are studied and discussed through theoretical modeling and simulation.Theoretical modeling: Using angular spectrum propagation theory and fast Fourier transform(FFT)spectral transformation technology,a model of multi-phase screen in the atmospheric transmission of 1319&1064 nm dual-wavelength alternating pulse laser is established,and low-frequency harmonic compensation technology is used to improve the low-frequency characteristics of the phase screen,thus achieving more accurate transmission effect.By studying the phase screen of 1319&1064 nm double-wavelength alternating pulse laser propagation in atmospheric turbulence environment,a series of key parameters,such as grid number,phase screen spacing,grid size and number of phase screens,are given to improve the accuracy and reliability of phase screen simulation of1319&1064 nm double-wavelength alternating pulse laser transmission in atmospheric turbulence.The theoretical models of energy distribution,intensity flicker,light path fluctuation and pulse broadening are established to more accurately simulate the propagation of 1319&1064 nm dual-wavelength laser in the atmospheric environment.Simulation:The phase screens generated by inversion of harmonic compensated power spectrum are used to simulate atmospheric turbulence.The intensity and time difference of atmospheric echo of 1319&1064 nm double-wavelength alternating pulsed laser in different atmospheric environments are simulated.ΔT and the effect of pulse broadening,it is found that the echo intensity of 1319&1064 nm laser decreases significantly with the increase of turbulence intensity,and the energy loss of these two lasers increases with the increase of propagation distance.However,in the same atmospheric environment,the energy loss of1319 nm laser is lower than that of 1064 nm laser.Echo time difference of 1319&1064 nm double-wavelength alternating pulse laser with increasing transmission distance and particle reflectivity ΔT increases significantly because the 1064-nm laser pulse delay is greater than the 1319-nm laser pulse delay in the same atmospheric environment,and as atmospheric visibility increases,ΔT decreases gradually;When 1064 nm and 1319 nm dual-wavelength alternating pulsed laser are transmitted under the same conditions,their return pulse width ratio increases with distance.It decreases with increasing atmospheric visibility.