Recently, a research team from Shanghai Institute of Optics and Fine Mechanics (SIOM) of the Chinese Academy of Sciences (CAS) reported the generation of multicolor concentric ultrafast vortex beams (MUCU-VBs) with controllable orbital angular momentum. The results were published in Applied Physics Letters on February 7, 2022.

Ultrafast vortex beams have important applications in many fields, such as ultrafast optical tweezers, microparticle manipulation, super-resolution microscopy, novel ultrafast spectroscopy, chirality detection, and optical communication. Furthermore, the modulation of the vortex beam and its increased degrees of freedom, such as the extension of the wavelength of the vortex beam and the modulation of its space-time structure, will further expand its applications.

They propose a new method to generate MUCU-VBs in a YAG plate using cascaded four-wave mixing. Nine frequency up-conversion concentric vortex sidebands are generated, where the spectra of the first 6 sidebands extend from 550 nm to 750 nm with a spectral width of about 200 nm. The topological charges of the generated multicolor vortex beams can be easily controlled by changing the topological charges of the incident pump beams. Furthermore, these multicolor ultrafast vortex beams can be collimated and focused simultaneously, forming a multi-focus structure where the focal spots can be aligned in the beam propagation direction.

This research provides a new multicolor ultrafast vortex light source and also generation method. The generation setup is simple and compact. The method can be easily extended to the generation of MUCU-VBs in other spectral ranges, such as deep ultraviolet, ultraviolet, mid-infrared, far-infrared and even terahertz range.

Fig. 1. Experimental setup for the generation of multicolor concentric ultrafast vortex beams (MUCU-VBs). (Image by SIOM)

Fig. 2. (a) Photograph of the whole generated MUCU-VB on a sheet of white paper placed after the YAG plate. (b) The spectra of the first six (five) sidebands. (Image by SIOM)

Article website:
https://doi.org/10.1063/5.0081005

Contact:
WU Xiufeng
General Administrative Office
Shanghai Institute of Optics and Fine Mechanics, CAS
Email: xfwu@siom.ac.cn
Web: http://english.siom.cas.cn/