a) Experimental device for generating and measuring spatiotemporal vortices (ST) of light; BS: beam splitter. b) Diagram showing the method of measuring the phase of light. The figures in italics represent the relative phases for the vortexes. The numbers in italics represent phases relating to various places. Note that the phase increases clockwise. Credits: Andy Chong, Chenhao Wan / University of Dayton

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Generation of spatiotemporal optical vortices with controllable transverse orbital angular momentum



Andy Chong, Chenhao Wan, Jian Chen & Qiwen Zhan



Nature Photonics (2020)



https://doi.org/10.1038/s41566-020-0587-z

Scientists have known for decades that light rotates around a longitudinal axis parallel to the direction in which it travels. However, some specialist researchers are currently trying to establish whether there are other forms and states, and to what extent it would be possible to control this. Recently, researchers from the University of Dayton managed to create a new “state of light”, by making it “rotate” around a transverse axis perpendicular to the displacement.After two years dedicated solely to their study, Andy Chong and Qiwen Zhan, researchers from the University of Dayton in the United States, have for the first time managed to create a new “state of light”. As part of their experiment, they show that a beam of light can also rotate around a transverse axis perpendicular to the direction in which it moves, like a vortex. The results of the study were published on February 24 in the specialized journal Nature Photonics."The sabbatical allowed us the time to fully concentrate on this research and was very instrumental in putting us in a position to make this discovery," Chong said.Zhan and Chong didn't go into their research with preconceived notions on what to look for or what they would find."It was more of a curiosity. Can we do this or make light do that?," said Zhan, a professor of electro-optics and photonics and managing director of the UD-Fraunhofer Joint Research Center. "Once we discovered we're able to do this, we then asked 'what's next?'""What's next?" may be a while off for the researchers and others who will examine the pair's basic research findings for applications, but they surmise this new state of light could be used to improve the transmission of large amounts of data with greater security, among many other potential applications.The researchers demonstrate in particular that a three-dimensional wave packet that is a spatiotemporal (ST) optical vortex with a controllable purely transverse OAM. Contrary to the transverse SAM, the magnitude of the transverse OAM carried by the ST vortex is scalable to a larger value by simple adjustments.Since the ST vortex carries a controllable OAM uniquely in the transverse dimension, it has strong potential for novel applications that may not be possible otherwise. The scheme reported here can be readily adapted for other spectral regimes and different wave fields, opening opportunities for the study and applications of ST vortices in a wide range of areas."We don't know yet? But the sky's the limit," Zhan said. The duo is most interested in how the light interacts with materials. "We want to better understand how this state of light interacts with materials in space and time," said Chong, associate professor of physics and electro-optics and photonics.