Today, it is well known that light possesses a linear momentum that is along the propagation direction. Besides, scientists also discovered that light can possess an angular momentum, a spin angular momentum (SAM) associated with circular polarization and an orbital angular momentum (OAM) owing to the azimuthally dependent phase. Even though such angular momenta are longitudinal in general, an SAM transverse to the propagation direction has opened up a variety of key applications1. In contrast, investigations of the transverse OAM are rare due to its complex nature. Here, we demonstrate 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.
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All data of this study are available from the corresponding authors upon reasonable request.
All codes used for data analysis and simulations are available from the corresponding authors upon reasonable request.
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Supplementary Figs. 1–5, captions for videos 1–7 and refs. 1–9.
Experimental phase pattern movie as the reference pulse is scanned on the ST vortex with l = 1. The first two slides are beam profiles of the ST vortex and reference beam, respectively. The scanning step size is ~33 fs. The reference pulse duration is ~90 fs.
Theoretical phase pattern movie as the reference pulse is scanned on the ST vortex with l = 1.
Experimental phase pattern movie as the reference pulse is scanned on the ST vortex with l = −1. The scanning step size is ~33 fs.
Experimental phase pattern movie as the reference pulse is scanned on the ST vortex with l = 2. The scanning step size is ~33 fs.
Theoretical phase pattern movie as the reference pulse is scanned on the ST vortex with l = 2.
Experimental 3D iso-intensity movie of the ST vortex with l = 1.
Experimental 3D iso-intensity movie of the ST vortex with l = 2.
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Chong, A., Wan, C., Chen, J. et al. Generation of spatiotemporal optical vortices with controllable transverse orbital angular momentum. Nat. Photonics 14, 350–354 (2020). https://doi.org/10.1038/s41566-020-0587-z