Amplification of light pulses with orbital angular momentum (OAM) in nitrogen ions lasing

Connected to paperThis paper is a preprint and has not been certified by peer review

Amplification of light pulses with orbital angular momentum (OAM) in nitrogen ions lasing


Haicheng Mei, Jingsong Gao, Kailu Wang, Jiahao Dong, Qihuang Gong, Chengyin Wu, Yunquan Liu, Hongbing Jiang, Yi Liu


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 +1 and -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.

Follow Us on

1 comment


This is a supplementary video that dynamically captures how we do this experiment as presented in the paper. We record this because a good overlap between the pump and seed beams is crucial for the achievement of a vortex beam amplification in cavity-free air lasing. Misalignment of the pump and seed leads to the degeneracy of the amplified OAM beam to a Gaussian beam. Some other researchers have done this experiment under the condition of misalignment, and they observed a vortex beam was amplified into a Gaussian beam. As a result, they gave a mysterious conclusion that the phase information of the seed pulse was wiped off in the amplification process, which is contrary to Maxwell's equations. The video shows in which experimental conditions one would observe a Gaussian output.

Add comment