Critical Techniques For Spectral-interferometry-based Ultrafast Dynamic Measurement System And Application

Ultrafast phenomena refer to the physical or chemical processes that occur in the femtosecond and picosecond time scale,such as laser-driven shock wave process,ultrafast chemical reaction,etc.Since ultrafast phenomena are usually unrepeatable and occur in a very short time,it requires the measurement to be completed in one single pulse and the time resolution to reach picosecond or subpicosecond order of magnitude,which poses a great challenge to the measurement techniques and methods.According to the linear relationship between frequency and time of the chirped pulse,the measurement results in spectral domain of chirped pulse spectral interferometer(CPSI)can be directly mapped into time domain,thus CPSI can realize the single pulse metrology of ultrafast dynamic processes.This dissertation will focus on the critical techniques and application of the CPSIbased ultrafast dynamic measurement system,of which the main contents and innovations include:First,the CPSI-based single pulse measurement principle of ultrafast dynamic processes is investigated,and the theoretical CPSI model based on frequency-time mapping method is established.By analyzing the error sources and categorization in ultrafast measurement system,the theoretical model of the reference measurement error is built,and an error compensation algorithm is proposed to correct it.The actual measurement results of spectral interferogram verified the effectiveness of the proposed algorithm.Second,aiming at the large data processing error introduced by the factors,such as fringe truncation,fringe’s uneven distribution and window function’s profile,an improved data processing method is proposed.By adding a gaussian envelope on the fringe and extracting the alternating term with a self-designed flat-top cap window,the proposed method can dramatically reduce the data processing error.Numerical simulation results verified the effectiveness of the proposed method.At the meantime,through the simulation about noise and fringe density,the optimal fringe density of the spectral interferogram is predicted,which can help to improve the accuracy of ultrafast measurement system.Third,to realize the linear mapping relationship between frequency and time,a singlegrating-based chirped pulse stretcher system is designed and a precise calibration method based on the spatial chirp characteristics is proposed.With the stationary phase point method,the linear chirp coefficient of the stretched pulse is measured.Utilizing the above stretcher,a CPSI-based ultrafast measurement prototype system is designed and built,and some key techniques in the optical path adjustment and calibration are overcame.The performance evaluation of the ultrafast dynamic measurement system indicates that the spatial resolution is about 3.0 μm,the temporal resolution is about 3.6 ps,the phase measurement precision of the perturb signal is about 0.03 rad,and the amplitude measurement precision is about5%.At last,with the home-made measurement system,the basic research for application on shock wave loading experiment of transparent materials is carried out.Based on the pulse shaping method,a steady shock wave acquisition method is put forward.Then the dynamic optical model of transparent film samples under steady shock wave loading is established,and the theoretical formulas for extracting shocked dynamic parameters are derived.By breaking the limitation of the normal incident configuration in the traditional shock etalon method,an oblique measurement scheme that adopts the p-polarized light and the Brewster incident angle is proposed to extract shock dynamics parameters of transparent materials,which can avoid the measurement error introduced by the sample surface reflection.The shock compression experiment on transparent polycarbonate film samples demonstrated the effectiveness of the proposed method.The error analysis shows that the proposed method is robust to noise and the measurement configuration errors.In this dissertation,the theories,methods and techniques of single pulse metrology on ultrafast dynamic processes have been systematically investigated.With the home-made ultrafast measurement prototype system,a series of laser-driven shock wave loading experiments were carried out.Some innovative achievements have been made in error analysis and correction,data processing algorithm for spectral interferogram,design and calibration of the chirped pulse stretcher,construction of ultrafast measurement prototype system and performance evaluation,dynamic optical model of transparent material under shock wave loading and measurement method of shocked dynamic parameters.The work in this dissertation will promote the research progress in the field of ultrafast metrology,especially provide new methods for the measurement of shocked dynamic parameters of transparent materials,which can promote the progress and perfection in the field of laserdriven shock wave loading experiments in China.