面向激光等离子体尾波加速的毛细管放电实验研究

Experimental study on capillary discharge for laser plasma wake acceleration

具有合适径向密度分布的等离子体通道可以用于超短超强激光导引,这使得等离子体通道在激光尾波加速中有着重要的应用.本文介绍了在上海交通大学激光等离子体实验室开展的毛细管放电和光导引实验.通过光谱展宽法测量了充氦气的放电毛细管中的等离子体密度分布,在长度为3 cm、内径为300μm的毛细管中实现了轴向均匀,径向呈抛物线型的等离子体密度分布.通过改变放电延时和喷气时长,确定和优化了产生等离子体通道的参数区间,得到的最大通道深度为28μm,与实验中使用的激光焦斑半径匹配.在此基础之上,开展了不同能量的激光脉冲在放电等离子体通道中的导引研究,结果发现当通道深度与焦斑半径匹配时,激光可以不散焦地在通道中传输,实现激光导引.这项研究为未来的激光尾波级联加速和锁相加速等研究奠定了基础.

Preformed plasma channels play important roles in many applications,such as laser wakefield acceleration,plasma lens,and so on.Laser pulses can be well guided when the radial density distribution of the plasma channel has a parabolic profile and it is matched with the laser focus.Discharging a gas-filled capillary is a possible way to form such plasma channels.In this work,we report the capillary discharging and laser guiding experiments performed in the Laboratory for Laser Plasmas at Shanghai Jiao Tong University.The plasma density distributions in the Helium-filled discharged capillary are measured by using the spectral broadening method.In a capillary with a length of 3 cm and a diameter of 300μm,the plasma density profile is observed to be uniformly distributed along the axial direction and have a parabolic profile along the radial direction.Parameters for plasma channel generation are scanned.The deepest channel depth obtained is 28μm,which is close to the focal spot radius of the laser used in the experiment.Laser guidance in the plasma channel is also studied.The results show that the laser can maintain its focus and continuously propagate when the channel depth matches the focal spot,indicating that the well guiding of the laser pulse by the preformed plasma channel is obtained.These studies may serve as the ground work for the future studies,such as staged laser wakefield acceleration and phase-locked wakefield acceleration.