Rostami Shermineh, Chini Michael, Lim Khan, Palastro John P, Durand Magali, Diels Jean-Claude, Arissian Ladan, Baudelet Matthieu, Richardson Martin
Center for High Tech Materials, University of New Mexico, Albuquerque NM 87106, USA.
Townes Laser Institute, CREOL - The College of Optics and Photonics, University of Central Florida, Orlando FL 32816, USA.
Sci Rep. 2016 Feb 5;6:20363. doi: 10.1038/srep20363.
Broadband laser sources based on supercontinuum generation in femtosecond laser filamentation have enabled applications from stand-off sensing and spectroscopy to the generation and self-compression of high-energy few-cycle pulses. Filamentation relies on the dynamic balance between self-focusing and plasma defocusing - mediated by the Kerr nonlinearity and multiphoton or tunnel ionization, respectively. The filament properties, including the supercontinuum generation, are therefore highly sensitive to the properties of both the laser source and the propagation medium. Here, we report the anomalous spectral broadening of the supercontinuum for filamentation in molecular gases, which is observed for specific elliptical polarization states of the input laser pulse. The resulting spectrum is accompanied by a modification of the supercontinuum polarization state and a lengthening of the filament plasma column. Our experimental results and accompanying simulations suggest that rotational dynamics of diatomic molecules play an essential role in filamentation-induced supercontinuum generation, which can be controlled with polarization ellipticity.
基于飞秒激光丝状化中超连续谱产生的宽带激光源，已实现了从远距离传感与光谱学到高能量少周期脉冲的产生与自压缩等多种应用。丝状化依赖于分别由克尔非线性和多光子或隧道电离介导的自聚焦与等离子体散焦之间的动态平衡。因此，包括超连续谱产生在内的丝状化特性对激光源和传播介质的特性都高度敏感。在此，我们报道了在分子气体中丝状化时超连续谱的反常光谱展宽，这是在输入激光脉冲的特定椭圆偏振态下观察到的。所得光谱伴随着超连续谱偏振态的改变以及丝状等离子体柱的延长。我们的实验结果及相关模拟表明，双原子分子的旋转动力学在丝状化诱导的超连续谱产生中起着至关重要的作用，且这一过程可通过偏振椭圆率来控制。
