Research On Measurement Of Femtosecond Laser Pulse Based On Autocorrelation And Frequency-resolved Optical Gating Technology

In the half century since Maiman invented the laser in 1960,laser technology has maintained a high-speed development.During this process,the laser pulse width has also developed from the initial microsecond order to the current femtosecond order,and even the attosecond order.Ultrafast lasers have epoch-making significance in helping humans expand their understanding of physical processes at extreme time scales due to their extremely short pulse duration.Emerging technology means that people can observe the transition state of atoms and molecules in the process of material reaction through "slow motion".Bringing a new revolution to the fields of chemistry,materials,energy,optoelectronics and related sciences.On the other hand,the shortening of the pulse width and the increase of the energy of the single pulse have further pushed the peak power of the laser to several watts,providing new research tools for accelerator physics,high energy physics,nuclear physics and other disciplines.The emergence of such lasers with extreme time scales and powers not only provides us with powerful tools for exploring unknown parameter spaces,but also puts forward higher requirements for the corresponding laser measurement technology.The technology of laser pulse width measurement has also experienced the development of direct measurement of nanosecond lasers using fast photodiodes and measurement of picosecond lasers using fringe cameras.However,none of the above methods can measure the width of the femtosecond pulse,so people have developed a method of measuring the optical pulse itself using femtosecond light pulses.Among them,the representative ones include autocorrelation,frequency-resolved optical gating method,and spectral phase coherence.Electric field reconstruction method,etc.In this paper,the research work of two laser pulse measurement methods of autocorrelation and frequency-resolved optical gating method is selected.The main contents of the paper are as follows:(1)The dependence of the second-harmonic bandwidth and center wavelength of the ultra-short laser pulse to be measured with a broadband spectrum in a nonlinear crystal on the crystal parameters is studied,and the ultra-short laser pulse width based on the second harmonic signal is clarified Measurement technology requirements for nonlinear crystal parameters.(2)Design and build a single-shot autocorrelation instrument that can accurately measure the ultra-short laser pulse width,and has the characteristics of compact structure,convenient portability,and flexible measurement.And the corresponding visual measurement and control software was developed based on Labview environment.The effect of dispersion on the pulse width measurement of broadband ultrashort laser pulses is studied.The experimental device was built and the experiment of measuring laser pulse width was carried out.(3)Design and build a frequency-resolved optical gating apparatus that can simultaneously measure the ultra-short laser pulse width and spectral phase.The performance characteristics of chirp and self-phase modulation effects on the trace graph are analyzed,and the effects of these effects on pulse width and phase measurement are studied,thereby optimizing and improving the accuracy of the measurement results.