Visualization of long-range plasma in a single shot for femtosecond laser nonlinear propagation in molecular gases

In this work, we conduct experimental and theoretical studies of the plasma dynamics in femtosecond laser filamentation [1] for various molecular gases (N₂, CO₂ and air) which exhibit strong rotational Raman nonlinearities [2]. In our pump-probe experiments, we vary the pulse duration of a filamenting pump laser to utilize the delayed Raman response of molecular gases and employ a single shot probe imaging method [3] to visualize/ measure the plasma density along the extended plasma channel. To compare with the experiments, we carry out nonlinear envelope equation simulations, in particular, by using the highly sophisticated alignment-dependent molecular ionization model (MO-PPT) [4].

[1] Couairon and A. Mysyrowicz, Physics reports 441,47-189; [2] H. Stapelfeldt and T., Seideman, Reviews of Modern Physics 75, 543 (2003); [3] Z. Li, et al., Optics Letters 38, 5157 (2013);[4] S. F. Zhao, et al., Physical Review A 93.023413 (2016).