Wakefield-based Few-Cycle Pulse Compression With High Energy

Few-cycle ultrashort pulses have a wide range of applications in physics and engineering.Obtaining few-cycle pulses with large-energy and high-intensity has been a research hotspot in recent years.Various methods to generate few-cycle pulses have emerged one after another,such as multi-pass cell compression,pulse compression in hollow-core fibers and so on.The pulse compression scheme using these nonlinear media can generate ultrashort pulses with a sub-10 fs pulse width,but the energy of the pulse is often limited by the damage threshold of the media and cannot reach more than 10m J.In contrast,there is currently another pulse compression scheme using plasma wakefield.The advantage of this method is that the damage threshold does not need to be considered,so high-energy and high-intensity pulses could be used in this method.Although the input pulse energy used in the pulse compression scheme based on the wakefield is on the order of Joules so far,people haven't generated 800nm few-cycle pulses above 10m J in the experiments.In this article,we propose a pulse compression scheme using quasi-nonlinear wakefield,which can generate 20m J few-cycle pulses of 800nm center wavelength in simulation.We use Particle in cell simulation experiments to verify the pulse compression scheme.The 3D particle simulation code used is Osiris,which is reliable and widely used.In the article,a33.5m J,30fs pulse is used as the input,and a underdense uniform plasma with an electron density on the order of 10¹⁹cm^3-when fully ionized is used as a non-linear medium.The pulse interacts with the plasma to excite the quasi-nonlinear wakefield,and the spectral gets broadened by self-phase modulation.Through the comprehensive use of self-compression and external dispersion management,we finally obtain a few-cycle pulse with large energy and unchanged center wavelength.The main innovations in this work are:the pulse spectrum achieves symmetrical broadening;the compressed pulse keeps the center wavelength of the input pulse unchanged,which is still 800nm;the input pulse near the critical power realizes stable transmission and compression;the wakefield used is a quasi-nonlinear wakefield instead of a highly non-linear one;a combination of pulse self-compression and external dispersion management is used for pulse compression.In addition,we analyze in detail the changes in the frequency spectrum during the laser-plasma interaction process to find the factors affecting the symmetry of the spectral;we comprehensively compare the effects of linear,quasi-nonlinear and nonlinear wakefield on the spectral broadening;we analyze the effects of self-focusing and wakefield constraints on pulse compression in the case of 3D.On this basis,we found a suitable parameter range,and finally obtained a relativistic pulse with a good spatial distribution and high beam quality on the axis.