Pulse shape of ultrashort intense laser reflected from a plasma mirror
Wigner distribution (left axis) and temporal profiles (right axis) of laser pulse after reflection from PM with Fpm. (a) 140.0 J/cm2, (b) 50.0 J/cm2, (c) 23.8 J/cm2，(d) 14.0 J/cm2，(e) 9.2 J/cm2, (f) 6.5 J/cm2.
The interaction of ultrashort intense laser with plasma could produce energetic particles (electrons, positrons, neutrons and ions) and ultrafast radiation sources from microwave to γ-ray. These novel secondary sources have promising applications in the material science, medical biology and future energy. With the increase of achievable intensity of high-power lasers, the requirement of higher temporal contrast, has been a growing issue for efficiently producing these sources.
Plasma mirror (PM) is a robust technique in improving the laser temporal-intensity contrast which is widely used in almost all the high-power laser laboratories. The contrasts of PM-reflected laser pulses are generally characterized in nanosecond and picosecond time scales. However, laser temporal profiles of PM-reflected laser pulse in sub-picosecond regime have not been investigated experimentally. The pulse duration after employing the PM was thought to be unchanged in analyzing the experimental data.
The research group led by Prof. Jie Zhang has measured, with high temporal resolution in the sub-picosecond window, the laser temporal profiles, spectra and phase of the PM-reflected pulse as a function of laser fluence on PM. They found that the leading front and the width of laser pulses depend sensitively on the incident laser phase and fluence on PM surface. Spectral modulation was found to play a key role in pulse profile shaping. The prepulse-suppressed laser pulses have important applications in the interaction of laser with ultra-thin solid target. The results will extend our knowledge on proper utility of plasma mirror technique for temporal contrast improvement and applications. This work has been published in Chinese Optics Letters, Volume 16, Issue 10, 2018 (Xulei Ge et al., Pulse shape of ultrashort intense laser reﬂected from a plasma mirror).
"The prepulse-free laser pulses could find important applications in more advanced ion acceleration schemes, such as radiation-pressure acceleration, and high harmonic generations from solids." said Dr. Xiaohui Yuan from the research group. The relevant experiments are being planned by using the PM technique.
不同激光能量密度下测量的反射激光的Wigner 分布 (左轴) 和脉冲时间波形（右轴）。(a) 140.0 J/cm2, (b) 50.0 J/cm2, (c) 23.8 J/cm2，(d) 14.0 J/cm2，(e) 9.2 J/cm2, (f) 6.5 J/cm2
张杰教授领导的课题组通过改变入射到等离子体镜上的激光能量密度，研究了等离子体镜反射的激光脉冲时间波形与入射激光脉冲的相位和能量密度的关系。结果发现，随着激光能量密度的降低，激光脉冲前沿逐渐被压制，脉宽展宽。激光脉冲在时间上的整形与激光光谱的调制密切相关。这一结果拓展了人们对等离子体镜技术的认识，并有助于更好地使用等离子体镜。相关研究结果发表于Chinese Optics Letters 2018年第16卷第10期（Xulei Ge et al., Pulse shape of ultrashort intense laser reﬂected from a plasma mirror)。