Research On Improving The Accuracy Of Dual Femtosecond Laser Ranging Based On Wavelet Transform Algorithm

In the development of human society,distance measurement has always played an extremely important role,and its measurement accuracy has also become an important indicator in the fields of aerospace technology,equipment processing and manufacturing,and precision measurement.With the development of science and technology and the deepening of scientific research,people have been pursuing higher absolute ranging accuracy.Traditional laser ranging has been difficult to meet the large-scale,high-precision,real-time measurement requirements in current industrial scenarios.The emergence of femtosecond laser frequency combs provides a technical method to solve this problem.The pulse width of the ultrashort pulse signal emitted by the femtosecond mode-locked laser is in the order of femtoseconds,and has a high time resolution.Using this method for distance measurement can obtain a high distance resolution.Because of its high measurement accuracy,long range and fast update rate,it has become a research hotspot at home and abroad in the past decade.With the continuous development of optical frequency comb technology,the miniaturization and integration of ranging systems are also expected to be widely used in future scientific research and processing and manufacturing fields.In order to integrat dual-comb ranging system,the dual optical comb technology better application to precision measurement in the field of industry,to overcome the complex work environment,at the same time,considering the cost problem,the future industrial application in as far as possible under the premise of meet the requirements of high precision,real-time,simplified experiment ranging system,The repetition frequency of two femtosecond lasers with a certain repetition frequency difference is locked,but the offset frequency is free operation,so the ranging accuracy will have a certain degree of loss.The main task of the thesis is to improve the ranging accuracy as much as possible through the algorithm under the existing experimental conditions to meet the needs of the current project.The method of double comb ranging is that the pulse light emitted by the signal laser is reflected by the reference target and the measurement target respectively,and the reflected light interferes separately with the pulse light of another local oscillator laser.By means of asynchronous optical equivalent sampling,the interference signal is presented in the rf domain.In order to measure the optical path difference between light and reference light accurately,it is usually necessary to effectively resolve the envelope information from the interference signal.At present,the two-comb ranging signal envelope extraction algorithms mainly include Hilbert transform algorithm and Fourier transform algorithm.However,in the actual application process,the noise will affect the carrier signal,causing the envelope peak extracted from the carrier to fluctuate greatly,which seriously affects the measurement adaptability and ranging accuracy.In this thesis,the wavelet transform algorithm is applied to the double-comb absolute distance measurement method.Due to the multi-resolution and multi-scale analysis characteristics of the wavelet algorithm,the interference of noise can be effectively suppressed,the extracted envelope is more accurate,and the interference of noise can be effectively improved.stability and measurement accuracy.During the experiment,the system noise was first filtered by the wavelet noise reduction algorithm to reduce the influence of noise on the data,then the envelope of the carrier was fitted by the envelope extraction algorithm of wavelet transform,and finally the envelope was fitted with Gaussian to further reduce the noise.System error,improve ranging accuracy.The research content of this thesis is mainly divided into the following parts:1)Review of femtosecond laser absolute distance measurement field of research present situation,study the optical frequency comb and double optical comb absolute distance measurement system of the theoretical basis,this paper optical asynchronous equivalent sampling principle,by using the threesome laser is analyzed on the reasons of absolute distance measurement can get high precision,and then introduces the data processing algorithm process2)Data processing includes noise processing and envelope extraction.Firstly,by introducing the advantages and disadvantages of Fourier transform algorithm principle,the advantages of wavelet transform algorithm in noise processing are introduced,and the reasons and process of wavelet denoising algorithm are introduced.Then the principle of extracting signal envelope by Hilbert transform algorithm and wavelet transform algorithm is introduced.The measurement accuracy can be improved by setting appropriate parameters through experiments.3)In the experimental aspect,the use of two heavy with a certain frequency difference of femtosecond laser absolute distance measurement,introduces the experimental device of parameter Settings,ranging accuracy by Allen variance evaluation system,through the comparison of multiple sets of experiments verify the wavelet transform algorithm in dealing with a range will get higher ranging accuracy,the accuracy of about 10?m.