Simulation study of the self-compression of a sub-TW laser pulse in a dense gas target

Dang Khoa Tran^1*, Yao-Li Liu², Shao-Wei Chou², Shih-Hung Chen², Ming-Wei Lin^1,2

¹Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu,300044, Taiwan
²Department of Physics, National Central University, Jhongli,32001, Taiwan

* Presenter:Dang Khoa Tran, email:trandangkhoavietnam@gmail.com

Self-compression of a sub-terawatt(TW) laser pulse can be achieved when the pulse is propagating in a thin, dense gas target; in this way, the interplay of ionization of gas atoms, defocusing, and diffraction of laser fields cause the phase modulations and the spectral broadening needed to realize a short duration for the output pulse. Through three-dimensional particle-in-cell simulations, selected focal spot sizes and focal positions of the incident pulse are assigned in conjunction with the variation of peak density and gas specie of the target to investigate the performance of pulse compression. When a 0.25-TW, 40-fs, 810-nm pulse is incident into a nitrogen target having a 120-μm wide Gaussian density profile and a peak plasma density of 8×10¹⁹ cm^-3 , a shortest output duration ~23 fs is acquired with the focal spot size of 4 μm and the focal position at 50 μm before the density peak. Under the same rest of parameters, a reduced pulse duration of 19 fs is resulted when a hydrogen target is applied to inhibit the undesired ionization-induced defocusing. Moreover, using a greater peak density of 1.2×10²⁰ cm^-3 for the hydrogen target allows the 0.25-TW pulse to be self-focused to an intensity capable of exciting a nonlinear plasma waves, which in turn modulates the pulse envelop and compresses the pulse to ~ 7 fs. Consequently, a significantly increased peak power ~ 1.3 TW is accomplished for the output pulse with an overall energy transmission ~ 90.5 %.

Keywords: self-compression, plasma nonlinear optics, particle-in-cell simulation