Research On The Measurement Of Ultrashort Pulse Characteristics Based On Dispersion Scan

With the development of modern laser technology,laser pulse with shorter pulse width and higher peak energy has become a hotspot of frontier domains.The pulse width of laser pulse has much developed from the beginning magnitude of micrometer into the magnitude of femtosecond.Including the initial CW laser and pulse laser,femtosecond laser are used extensively and stably.In labs,pulse that reach the magnitude of attosecond(10-18s)has been found.Using the high-order harmonic effect,ultrashort pulse can achieve into optical cycle level,even divided into single attosecond pulse.Hens,scientists can use it in observing and controlling of the delegate physical progresses and chemical reactions in attosecond magnitude.This type of laser pulse possess extremely wide spectrum and high peak power reaching PW(1015W).The exact width of pulse and the phase distribution of this type of pulse are essential characteristics of laser,while an exact and fast measurement of pulse width and phase distribution is very significative for applications in various fields.At present,mature pulse width measurement methods include autocorrelation,frequency-resolved optical gate(FROG),and spectral phase interferometry for direct electric-field reconstruction(SPIDER).Recently,new paradigm in pulse characterization based on phase scanning,multiphoton intra pulse interference phase scan(MIIPS)and dispersion scan(d-scan)are introduced,which are able to obtain not only the pulse width but also the phase distribution.The method of dispersion scan has multiple advantages including the clear theory in which we analysis the effect of chirp dispersion in second harmonic generation to retrieve the phase distribution characteristic of incident pulse,the simple experimental facility that contains no beam split and rebound,while the employment of off-axis parabola is used to compact the facility and the reusable iterative algorithm which is much familiar with algorithm used in FROG.Multiple possibilities in algorithm allows us to retrieve the spectral intensity and characteristics.Among this paper,a facility of dispersion scan is set up in lab for the specific requirements of our laboratory.Also,a software for semi-automatic continuous measurement is written and the iterative deduction algorithm is completed.This paper includes the following work contents:(1)Describing the correlation principles of dispersion scan method.Explaining the relation between SHG time domain character of ultrafast pulse and introduced dispersion.Comparing the advantages and disadvantages of different multi-dimensional optimization problem solutions in this algorithm.(2)Simulation of the continuous time domain based on Matlab.Program of discrete Fourier transform function towards frequency domain.Simulation of initial dispersion effect on d-scan figure.Coding the iterative algorithm based on downhill simplex method.Completing the error estimation.And studying the influence of the preset phase curve to iteration process.(3)Setting up the complete d-scan optical path,and realize the continuous change of step length of dispersion.Studying the effect of glass wedge mirror's parameters and chirp mirror's parameters on the light path.Allowing the use of thicker glass wedge mirrors through multiple reflections.Measure the laser pulses emitted by the femtosecond oscillator in laboratory.(4)Realizing the automatic control of the linkage between spectrometer and the electric displacement platform based on Labview.Export data that can be applied directly to the Matlab algorithm from the continuous measurement software...