Software Design And Implementation Of Photon Autocorrelator

The atmospheric boundary layer has obvious turbulence characteristics,and the temperature pulsation is the most important physical quantity in the turbulence parameter,which can be expressed by superimposing the small temperature change and the average atmospheric temperature in a short time.Due to the high degree of disorder and randomness in the generation and development of turbulence,whether using early slow response instruments or recent air balloons equipped with ultrasonic temperature difference anemometers and platinum wire temperature pulse fast response instruments,it is difficult to measure the data on the atmospheric boundary layer temperature pulsation profile with the detection period of Is and sensitivity of 0.1K.Therefore,the paper proposes a new method of dynamic light scattering lidar which combines the Photon Correlation Spectroscopy(PCS)with lidar working mechanism for temperature pulsation profile detection in atmospheric boundary layer:The spectral resolution of PCS with high spectral resolution can reach 10-14 and the response time of its main equipment-photon counter and autocorrelator can reach tens of picoseconds;the spectral resolution of the hyperspectral lidar with the Fabry-Perot etalon(FPE)and iodine molecular absorption cell as a spectroscopic device can be on the order of 100 MHz.The photon correlation instrument is the core device of PCS,and its function is to acquire the correlation function of the lidar echo signal.This paper analyzes and contrasts the existing implementation of photon correlation instrument in detail,and investigates the performance parameters of commercial photon correlation instrument on the market.Finally,it is proposed to use LSI Correlator to obtain the correlation spectrum of atmospheric molecular scattering light in the dynamic light scattering lidar system.LSI Correlator's advanced hardware design enables correlation calculations for multiple lag time and linear lag time,covering a lag time axis from 12'5 ns to 3436 s by 322 channels,which can span the largest lag time range available adjustable lag time based on its hardware logic,and uses a Field-Programmable Gate Array(referred to as FPGA)to verify the feasibility.The multi-channel photon autocorrelation software with adjustable lag time is designed with 16 lag time combined with 322 physical channels,and the dynamic range is up to 25.5ms to 2550ms,which avoids the shortcomings of linear correlator's small dynamic range and exponential multi-tau correlatior's low calculation accuracy due to the excessive growth rate of lag time.The overall design idea of the multi-channel photon autocorrelation software with adjustable lag time is top-down and modular layered.The specific modular design is divided into:lag time generation module,dual-counter module,autocorrelation operation module and communication module,etc.Each module can work independently,and the overall operation of the software is constrained by sequential logic.The software is simulated by Modelsim software to verify the correctness of its sequential logic.The accuracy of the autocorrelation operation results is verified by Matlab's autocorrelation function.The hardware verification of the photon autocorrelation software is Cyclone V's 5CSEBA6U2317 chip and uses the Tektronix AFG3252 signal generator to simulate the lidar echo signal(Rayleigh-Brillouin scatter signal0which is sent to the FPGA for overall testing.The final data can relatively accurately invert the spectral width of the input signal,which proves that the photon autocorrelation software is feasible,and the combination of PCS and the lidar working mechanism to obtain the atmospheric molecular characteristic parameters is practicable.