Flow Velocity Measurement Method Based On Femtosecond Laser

With the coming of the maritime era,many countries in the world have attached more and more importance to the oceans,and also have already begun to exploit and utilize the marine resources.They have added more and more ocean-related researches and achieved fruitful results.However,those have made a tremendous impact on the marine environment.It is important to utilize the ocean reasonably,which is related to our human beings' sustainable development.In the study of marine environmental science,the velocity of the current is one of the most crucial elements.In order to realize the purpose of contributing to the marine environmental science,we applied the femtosecond laser technology,which is a super star in the field of metrology for its outstanding performance,in the measurement of the speed of the current.We used the advantage of its repetition frequency can be traced to the microwave frequency reference to study a high-accuracy method of current measurement.This method can provide a technical reserve for the research of marine environmental science.First of all,combined with the mature optical frequency comb phase detection absolute distance measurement technology,we did some experiments to verify the feasibility and high accuracy of using the femtosecond laser in the field of velocity measurement.Then Doppler shift of every frequency component leading to the Doppler shift of repetition frequency is deduced by theoretical analysis and MATLAB simulation.Through measuring the velocity of a moving mirror,the accuracy of this method can reach submillimeter per second when applied in low speed measurement was verified.Finally,the flow velocity measurement experiment was conducted to verify the feasibility and accuracy of this method.The research content of this thesis can provide theoretical basis and technical support for acquiring accurate ocean current data,and provide a technical reserve for marine environmental science research.