Wang W-M, Sheng Z-M, Wu H-C, Chen M, Li C, Zhang J, Mima K
Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, CAS, Beijing 100190, China.
Opt Express. 2008 Oct 13;16(21):16999-7006. doi: 10.1364/oe.16.016999.
Mechanism of terahertz (THz) pulse generation in gases irradiated by ultrashort laser pulses is investigated theoretically. Quasi-static transverse currents produced by laser field ionization of gases and the longitudinal modulation in formed plasmas are responsible for the THz emission at the electron plasma frequency, as demonstrated by particle-in-cell simulations including field ionization. The THz field amplitude scales linearly with the laser amplitude, which, however, holds only when the latter is at a moderate level. To overcome this limitation, we propose a scheme using chirped laser pulses irradiating on tenuous gas or plasma targets, which can generate THz pulses with amplitude 10-100 times larger than that from the well-known two-color laser scheme, enabling one to obtain THz field up to 10MV/cm with incident laser at approximately 10(16)W/cm(2).
从理论上研究了超短激光脉冲辐照气体中太赫兹（THz）脉冲产生的机制。气体的激光场电离产生的准静态横向电流以及形成的等离子体中的纵向调制，是在电子等离子体频率处产生太赫兹辐射的原因，这通过包括场电离的粒子模拟得到了证明。太赫兹场振幅与激光振幅呈线性比例关系，然而，这仅在激光振幅处于中等水平时成立。为了克服这一限制，我们提出了一种使用啁啾激光脉冲辐照稀薄气体或等离子体靶的方案，该方案能够产生比著名的双色激光方案大10 - 100倍振幅的太赫兹脉冲，使得在入射激光约为10(16)W/cm(2)时能够获得高达10MV/cm的太赫兹场。
