Transverse structure and energy deposition by a subTW femtosecond laser in air: from single filament to superfilament
Transverse structure and energy deposition by a subTW femtosecond laser in air: from single filament to superfilament
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空气中亚TW飞秒激光的横向结构和能量沉积：从单丝到超丝
DOI：
10.1088/1367-2630/ab043f
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发表时间：
2019
影响因子：
3.3
通讯作者：
A. Savel’ev
中科院分区：
文献类型：
--
作者：
D. Pushkarev;E. Mitina;D. Shipilo;N. Panov;D. Uryupina;A. Ushakov;R. Volkov;A. Karabutov;I. Babushkin;A. Demircan;U. Morgner;O. Kosareva;A. Savel’ev
我们在实验上跟踪了在强流松聚焦（NA = 0.0021）飞秒激光束作用下单根空气丝到超细丝的转变。利用两个制度与复丝形成的人工振幅或固有的振幅/相位前调制的光束具有10-60的临界功率P cr。利用宽带声探测和束模成像单次激发技术，研究了沿着光路不同距离处灯丝的横向空间结构和能量密度，结果表明，只要初始束的峰值功率P不超过20 Pcr，在本征波前调制的情况下，可以形成一个极长的电离通道。它的体积能量密度比单丝高1.5-3倍，而线能量密度几乎高10倍。人工振幅调制导致在相同的初始条件下形成单个长灯丝或两个紧密间隔的灯丝。最大体积能量密度在两种情况下是相同的，并且略小于没有这种调制的情况。在较高的峰值功率P下产生几个紧密间隔的细丝，体积和线性能量密度随着P经历快速的非线性增加。体积能量密度也增加了10倍，达到1800 mJ cm− 3，证明强度和电子密度的巨大增加是超极化的特征。这些发现得到了基于Forward麦克斯韦方程的数值模拟的支持，该方程具有场的解析驱动器，其显示了超细丝分裂并确认了从实验数据估计的能量密度。
We traced experimentally transition from a single air filament to the superfilament under action of powerful loosely focused (NA∼ 0.0021) femtosecond beam. Two regimes were exploited with multifilament formation by artificial amplitude or intrinsic amplitude/phase front modulation of the beam having 10–60 critical powers P cr. Transverse spatial structure and energy density in the filament were studied using wideband acoustic detection and beam mode imaging single shot techniques at different distances along the optical path. We showed that with intrinsic front modulation a single extremely long ionized channel is formed provided peak power P of the initial beam does not exceed 20P cr. Its volumetric energy density is∼ 1.5–3 times higher than in the single filament, while linear energy density is almost 10 times higher. Artificial amplitude modulation leads to formation of either a single long filament or two closely spaced filaments at the same initial conditions. Maximal volumetric energy density was the same in both cases and slightly less than without this modulation. A few closely spaced filaments are generated at higher peak powers P with volumetric and linear energy densities experiencing fast nonlinear increase with P. Highest linear energy density achieved was 600 μJ cm− 1, ie almost 100 times higher than that of the single filament with increase in energy 10 times only. The volumetric energy density also increases by a factor of 10 to∼ 800 mJ cm− 3 proving huge increase in intensity and electron density that is characteristic feature of the superfilamentation. These findings were supported by the numerical simulations based on the Forward Maxwell equation with resolved driver of the field that showed superfilament splitting and confirmed energy densities estimated from the experimental data.
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