Zhang Wei, Chen Junyan, Wang Shuo, Li Helong, Zang Hongwei, Xu Huailiang
Opt Express. 2023 Sep 25;31(20):33132-33140. doi: 10.1364/OE.500042.
The efficiency of energy coupled to plasma during femtosecond (fs) laser filamentation plays a decisive role in a variety of filament applications such as remote fabrication and spectroscopy. However, the energy deposition characterization in the fs laser filament formed by a telescope, which provides an efficient way to extend the filament distance, has not yet been revealed. In the present study, we show that when the distance between the two lenses in a telescope changes, i.e., the effective focal length changes, there exists an optimal plateau energy deposition region in which the energy deposited into the filament per unit length called the average lineic energy deposition (ALED) remains at high levels, exhibiting a remarkable difference from the monotonic change in a single-lens focusing system. As a proof of principle, we examined the influence of the energy deposition on the ignition of a lean methane/air mixture, and found that the use of the telescope can efficiently extend the ignition distance when compared with a single-lens focusing system under the same incident laser energy condition. Our results may help understand the energy deposition behaviors in a variety of telescopic filaments and provide more options to manipulating laser ignition at a desired distance.
在飞秒（fs）激光成丝过程中，耦合到等离子体中的能量效率在诸如远程制造和光谱学等各种成丝应用中起着决定性作用。然而，由望远镜形成的飞秒激光丝中的能量沉积特性尚未被揭示，而望远镜提供了一种扩展丝长的有效方法。在本研究中，我们表明，当望远镜中两个透镜之间的距离发生变化，即有效焦距发生变化时，存在一个最佳的平台能量沉积区域，在该区域中，每单位长度沉积到丝中的能量（称为平均线能量沉积，ALED）保持在较高水平，这与单透镜聚焦系统中的单调变化表现出显著差异。作为原理验证，我们研究了能量沉积对贫甲烷/空气混合物点火的影响，发现在相同的入射激光能量条件下，与单透镜聚焦系统相比，使用望远镜可以有效地延长点火距离。我们的结果可能有助于理解各种望远镜丝中的能量沉积行为，并为在所需距离操纵激光点火提供更多选择。
