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

TL;DR

This paper demonstrates the amplification of light pulses carrying orbital angular momentum in nitrogen plasma, showing significant energy gain and the ability to switch between OAM and Gaussian modes through spatial alignment control.

Contribution

It introduces a method to amplify OAM-carrying light in nitrogen plasma and demonstrates mode switching via spatial misalignment, advancing OAM laser technology.

Findings

OAM pulses are amplified by two orders of magnitude in nitrogen plasma.

The amplified OAM pulses retain their original topological charge.

Spatial misalignment enables switching between OAM and Gaussian modes.

Abstract

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.