Researchers at Osaka University discovered the phenomenon of reciprocating propagation of laser pulse intensity in free space
Space-time coupling is used to generate light with adjustable group velocity, direction and trajectory in free space. For example, the flying focus (laser pulse intensity moving in the extended Rayleigh length), in which longitudinal chromatic aberration and time chirp are combined to control the spectrally dependent focus separation in space and the spectrally dependent pulse position in time, respectively. It has any adjustable speed and direction of propagation group in space and time.
However, in the previous results, although the propagation group speed can be freely controlled, the focus of flight can only propagate forward or backward in a certain direction.
In this research, by greatly increasing the Rayleigh length in space and the singular point in time, the newly generated flight focus propagates along a reciprocating straight line in free space. By further adding time singularities, a clear reciprocating flying focus with high spatial resolution becomes possible.
“Newly generated flight focus edge The longitudinal axis first propagates forward, then propagates backward, and finally propagates forward again, showing a reciprocating linear motion trajectory in space and time. The speed of forward propagation is the speed of light in a vacuum, and the speed of backward propagation It is sub-light speed,” corresponding author Zhaoyang Li explained.
This intriguing phenomenon has changed the traditional understanding of light propagation and may be applied to basic and applied physics. “For example, in our radiation pressure simulation, in the Rayleigh scattering system, it can generate a reciprocating capture force or thrust on a small ball or a large ball, respectively.”