Two-photon vibrational excitation of air by long-wave infrared laser pulses
Two-photon vibrational excitation of air by long-wave infrared laser pulses
复制标题
长波红外激光脉冲对空气的双光子振动激发
DOI：
10.1103/physreva.94.023816
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发表时间：
2016
影响因子：
2.9
通讯作者：
H. Milchberg
中科院分区：
文献类型：
--
作者：
J. Palastro;J. Peñano;L. Johnson;B. Hafizi;J. Wahlstrand;H. Milchberg
超短波红外（LWIR）激光脉冲可以通过双光子跃迁共振激发${\ mathm {N}}_{2}$和${\ mathm {O}}_{2}$中的振动。超快光学非线性的吸收振动分量随时间增长，开始时小于但很快超过电子、旋转和振动折射分量。振动分量的增长导致了一种新的三次谐波产生机制，提供了一个额外的双光子激发通道，基频+三次谐波。原始和涌现的双光子激发使共振完全非相位，引起吸收振动非线性的空间衰减。这几乎消除了双光子振动吸收。在这里，我们提出了模拟和分析计算，证明了这些过程如何改变空气中的超快光学非线性。研究结果揭示了超短脉冲在大气中传播时LWIR区特有的非线性光学现象。
Ultrashort long-wave infrared (LWIR) laser pulses can resonantly excite vibrations in ${\mathrm{N}}_{2}$ and ${\mathrm{O}}_{2}$ through a two-photon transition. The absorptive vibrational component of the ultrafast optical nonlinearity grows in time, starting smaller than but quickly surpassing the electronic, rotational, and vibrational refractive components. The growth of the vibrational component results in a novel mechanism of third-harmonic generation, providing an additional two-photon excitation channel, fundamental + third harmonic. The original and emergent two-photon excitations drive the resonance exactly out of phase, causing spatial decay of the absorptive vibrational nonlinearity. This nearly eliminates two-photon vibrational absorption. Here we present simulations and analytical calculations demonstrating how these processes modify the ultrafast optical nonlinearity in air. The results reveal nonlinear optical phenomena unique to the LWIR regime of ultrashort pulse propagation in the atmosphere.