Self-Compression Of Ultrashort Laser Pulses In Plasma

With the development of laser technology, especially ultrashort pulse ChirpedPulse Amplification technique,the width of laser pulse have been clearly at a range offemtosecond,output power of the laser has been increased for five-six orders ofmagnitude. The foci intensity(laser intensity)of the ultrashort pulse laser have been upto 1021w/cm2, even higher. The superstrength electric field of such intensive laser couldbrought far away greater than atom internal electric field,meanwhile it brings about asupervoltage greater than 1011bar and a very high magnetic field up to 104T's, and aBlack-Radiation with a temperature as high as 109K. In such strong electric fieldelectronic vibrating speed approaches the velocity of light. All above can bring hugeimpact and accident on many application subjects and broaden the physical researcharea greatly, propel the development of the high field physics.As an important part of high field physics, the research of laser plasma interactionat plasma self-focusing, particle acceleration technology, plasma filming technology aswell as realizing "rapidly ignition"laser fusion and other aspects are still in-depthresearching. And the self-focusing of the strong laser pulse transmiting in atmospherebody, loose solid material and other mediums cause some phenomena just like the laserpulse's self compression,filamentation and solitons. While the transmission of laserpulse in plasma forms pulse compression, soliton and paired solions, and densitycavitation of electron and ion and so on.Self Phase Modulation effect and Group Velocity Dispersion effect act intransmission of laser pulse in nonlinear media. With the increment of transmissiondistance, the frequency shifting resulted in SPM effect will increase, that is to say, freshfrequency component will be generated in the transmission of laser pulse in plasma.These generated photons enlarge the spectral band width of the laser pulse, and evengenerate shorter impulse. While chirp effect created by dispersion didn't generate freshfrequency, only reorder the different kinds of frequency involved in impulse.In this article, the nonlinear Schr?dinger equation of laser-plasma interaction isanalyzed, and the self–compression of femtosecond intense laser pulse in plasma atdifferent plasma density,the pulse width and intensity of laser pulse and otherparameters is studied. The results indicate that in a given range which plasma densityapproach critical density,laser light intensity approach relativistic light intensity, withthe increase of the width and the intensity of laser pulses, the self-compresssion effectduring the propagation of femtosecond intense laser pulse in plasma is strengthened.The higher the plasma density is, the more obvious the GVD effect is,and then the selfcompression in transmission of femto-second intense laser pulse in plasma is weakened.Distinct compression always appears in the propagation of laser pulse in plasmabecause the SPM effect is predominant.Moreover,change the plasma density,the pulse width and intensity of laser pulse,laser pulse is broaden. While the laser intensity a0=0.175, the initial pulse width T0 =5τand the plasma density N=0.3nc, we find that the soliton could approximately stabilizedpropagation in plasma by waken the self-compression effect properly.