Due to the ultrafast temporal characteristics of optical fields, direct spatiotemporal control of optical fields using optical modulation is nearly impossible. Therefore, traditional control methods exploit the wide spectral characteristics of ultrafast optical fields and the inherent physical correlation between the temporal and spectral domains. This is achieved through frequency-domain modulation combined with time-frequency transformation methods to achieve spatiotemporal composite control of ultrafast optical fields. A typical design is based on a +4 f imaging system using gratings, where amplitude/phase modulation is applied to the spectral surface to obtain different spatiotemporal coupled optical fields. However, this approach suffers from a series of drawbacks such as low spectral resolution, diffraction dispersion effects, and small control delays.

To address these issues, the research team has proposed a new mechanism for spatiotemporal coupled control of ultrafast optical fields: directly implementing spatiotemporal control of optical fields by introducing spatially correlated time delays combined with two-dimensional spatial geometric changes. To demonstrate the effectiveness of this new mechanism, the team further designed technical solutions to implement this mechanism. Through this approach, they experimentally obtained spatiotemporally coupled optical fields with simultaneous vortex distributions of amplitude and phase (referred to as "optical spring"). This optical spring was theoretically proposed a decade ago but has not been experimentally reported until now. It has a wide spectral topological charge in the frequency domain and a constant topological charge in the time domain. These characteristics make it 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 spatiotemporal coupled ultrafast optical fields can be obtained by controlling spatially correlated time delays and two-dimensional spatial geometric combinations. The related findings were published in Nature Communications, with Dr. Qinggang Lin from Shenzhen University and Dr. Fu Feng from Zhejiang Laboratory as co-first authors, and Professors Shixiang Xu and Xiaocong Yuan as corresponding authors. Shenzhen University is the first completing unit.

Paper link

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