Due to the ultrafast temporal characteristics of light fields, direct spatiotemporal control of light fields using optical modulation is nearly impossible. Therefore, traditional control methods utilize the broad spectral characteristics of ultrafast light fields and the inherent physical correlations between the temporal and spectral domains. They achieve spatiotemporal composite control of ultrafast light fields through frequency-domain modulation combined with time-frequency transformations. A typical design is based on a grating pair +4f imaging system, where amplitude/phase modulation is applied on its spectral surface to obtain different spatiotemporal coupled light fields. However, this approach suffers from a series of drawbacks such as low spectral resolution, diffraction dispersion effects, and minimal control delay.

To address these issues, the research team proposed a new mechanism for spatiotemporal coupled control of ultrafast light fields: directly implementing spatiotemporal control of light fields by introducing spatially correlated time delays combined with two-dimensional spatial geometric changes. To validate the effectiveness of this new mechanism, the team further designed technical solutions to implement it. Through this approach, they experimentally obtained spatiotemporally coupled light fields (referred to as "optical springs") with simultaneous amplitude and phase vortex distributions. This concept of optical springs was proposed in theory a decade ago but had not been experimentally reported until now. In the frequency domain, optical springs possess a broadband spectral topological charge, while in the temporal domain, they exhibit a constant topological charge. These characteristics make them promising for applications in laser-plasma dynamics, information encoding, laser-driven electron acceleration, vortex terahertz pulse generation, and other fields.

In the future, based on this control mechanism, different spatiotemporally coupled ultrafast light fields can be obtained by adjusting spatially correlated time delays and two-dimensional spatial geometric combinations. The related findings were published in "Nature Communications", with Dr. Lin Qinggang from Shenzhen University and Dr. Feng Fu from Zhejiang Laboratory as co-first authors, and Professor Xu Shixiang and Professor Yuan Xiaocong as co-corresponding authors, with Shenzhen University as the first completion unit.

Link

https://www.nature.com/articles/s41467-024-46802-x.pdf