Research On Femtosecond Pulses Shaping

Ultra-short pulse has been developing rapidly since its appearance.The femtosecond pulse has the advantages of short pulse duration,wide spectral range,high peak power and small focusing range,so that it can realize ultra-high spatial resolution as well as temporal resolution,which results in extensive and profound technological revolution.Ultra-short pulse has been widely used in physics,chemistry,spectroscopy,biomedicine,micro-processing,three-dimensional storage and other fields.When the femtosecond pulse is transmitted in the optical system,characteristics of the optical devices,such as the dispersion,aberration,surface-shape error and adjusting error,will have a serious impact on the pulse,resulting in pulse'broadening and even deformation and degradation of beam' quality,which brings about the poor performance of the whole optical system.Therefore,it is necessary to improve the pulse' quality by pulse shaping technology.So far,the research scope about ultrashort pulse is very wide,and the research methods are varied,but most of the research is confined to ideal lens or simple optical system,lacking the study about transmission of femtosecond pulse in practical complicated optical system.In this paper,based on the transmission characteristics of ultrashort pulses,the propagation of femtosecond pulses in optical systems is simulated by the combination of wave optics and geometrical ray tracing,especially in complex optical systems.In this way,the effect of spherical aberration and chromatic aberration on the femtosecond pulse is fully considered,and the broadening and deformation of the pulse can be analyzed.Generally,the positive dispersion of the optical material makes the propagation speed of the different spectral components different,i.e.the red light is faster than the blue one,so the red component and the blue component will gradually separate.As a result,the pulse width will increase,and the pulse peak power is reduced.The prism as well as the grating is a device with negative dispersion,through which blue light' transmission speed is faster than the red light'.The pulse light beam can be compressed and correction for the dispersion of ordinary optical materials,so that all the frequency components of the pulse propagates at the same time,and pulse width and peak power could be maintained.This method is used to simulate the propagation of femtosecond pulse in parallel plate.And then the extension of ultrashort pulse in three-piece lens is simulated,whose dispersion is compensated by prism.Finally,the simulation of ultrashort pulse in a large computational imaging instrument is made.Due to the complexity of the objective lens,the outgoing pulse experiences a serious extension and deformation.The grism(a combination of the grating and the prism)is proposed as a pre-correction scheme to compensate the dispersion of the complex optical system.When the suitable parameters are selected,the correction effect is much better,and the characteristics of the ultrashort pulse can be maintained to meet the actual demand.