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, Taiwan
²Department of Physics, National Central University, Jhongli, Taiwan

* Presenter:Dang Khoa Tran, email:s109013891@m109.nthu.edu.tw

Self-compression of a sub-terawatt(TW) laser pulse can be achieved when the pulse propagates in a thin, dense gas target; as a result, 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 [1,2]. 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 of the target to investigate the performance of pulse compression. When a 0.25-TW, 40-fs, 810-nm pulse is incident into a hydrogen target having a 120-μm wide Gaussian density profile and a peak plasma density of 8×10¹⁹ cm^-3, a shortest output duration ~20.2 fs is acquired with the focal spot size of 4 μm and the focal position at ∆x = -50 μm respective to the density peak. Moving the focal position away from this optimal one reduces the effect of pulse compression, because the region of high pulse intensity mismatches with the region of density peak, resulting in a weaker plasma response for driving pulse compression. 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 wave, which in turn modulates the pulse envelope and compresses the pulse to ~ 7 fs. Consequently, an enhanced peak power of 0.7 TW is accomplished for the output pulse with an overall energy transmission ~ 77.6 %.

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