Mei Haicheng, Gao Jingsong, Wang Kailu, Dong Jiahao, Gong Qihuang, Wu Chengyin, Liu Yunquan, Jiang Hongbing, Liu Yi
Opt Express. 2023 Sep 25;31(20):31912-31921. doi: 10.1364/OE.500041.
Nitrogen ions pumped by intense femtosecond laser pulses give rise to optical amplification in the ultraviolet range. Here, we demonstrated that a seed light pulse carrying orbital angular momentum (OAM) can be significantly amplified in nitrogen plasma excited by a Gaussian femtosecond laser pulse. With the topological charge of ℓ = ±1, we observed an energy amplification of the seed light pulse by two orders of magnitude, while the amplified pulse carries the same OAM as the incident seed pulse. Moreover, we show that a spatial misalignment of the plasma amplifier with the OAM seed beam leads to an amplified emission of Gaussian mode without OAM, due to the special spatial profile of the OAM seed pulse that presents a donut-shaped intensity distribution. Utilizing this misalignment, we can implement an optical switch that toggles the output signal between Gaussian mode and OAM mode. This work not only certifies the phase transfer from the seed light to the amplified signal, but also highlights the important role of spatial overlap of the donut-shaped seed beam with the gain region of the nitrogen plasma for the achievement of OAM beam amplification.
由强飞秒激光脉冲泵浦的氮离子在紫外波段产生光放大。在此，我们证明了携带轨道角动量（OAM）的种子光脉冲在高斯飞秒激光脉冲激发的氮等离子体中可得到显著放大。对于拓扑电荷ℓ = ±1的情况，我们观察到种子光脉冲的能量放大了两个数量级，同时放大后的脉冲携带与入射种子脉冲相同的OAM。此外，我们表明，由于OAM种子脉冲呈现出甜甜圈形状的强度分布这一特殊空间分布，等离子体放大器与OAM种子光束的空间失准会导致无OAM的高斯模式的放大发射。利用这种失准，我们可以实现一种光开关，在高斯模式和OAM模式之间切换输出信号。这项工作不仅证明了从种子光到放大信号的相位转移，还突出了甜甜圈形状的种子光束与氮等离子体增益区域的空间重叠对于实现OAM光束放大的重要作用。
