Physicists have demonstrated accelerating light beams on flat surfaces, where acceleration has caused the beams to follow curved trajectories. However, a new experiment has pushed the boundaries of what's possible to demonstrate in a lab. For the first time in an expeirment, physicists have demonstrated an accelerating light beam in curved space. Instead of traveling along a geodesic trajectory (the shortest path on a curved surface) it bends away from this trajectory due to the acceleration.
The study, published in the journal Physical Review X, "opens the doors to a new avenue of study in the field of accelerating beams. Thus far, accelerating beams were studied only in a medium with a flat geometry, such as flat free space or slab waveguides. In the current work, optical beams follow curved trajectories in a curved medium," according to Anatoly Patsyk, a physicist from the Israeli Institute of Technology.
Completed by physicists at Israel Institute of Technology, Harvard University, and the Harvard-Smithsonian Center for Astrophysics, the success of the experiment will increase research potential for further lab-based studies of phenomena like gravitational lensing. By performing these expeirments in a lab, scientists will be able to study such phenomena which stem from Einstein's general theory of relativity in a controlled setting.
The team first caused a laser beam to accelerate by reflecting the beam off a spatial light modulator, which is a device used to modulate amplitude, phase, or polarize light waves. Bouncing the beam off this device imprints a specific wavefront on the beam, creating one that accelerates while keeping its shape. The team then pointed the accelerating laser along the inside of an incandescent light bulb painted in such a way that the light both scattered and was visible to the researchers.
The team observed that when moving along the inside of the bulb, the beam's trajectory breaks apart from the geodesic line. When they compared this movement to a beam that was not accelerating, they found that when it was not accelerating, the beam would follow the line.
The research could be a starting point for future research into phenomena that fall within Einstein's general theory of relativity. Patsyk stated that "Einstein's equations of general relativity determine, among other issues, the evolution of electromagnetic waves in curved space. It turns out that the evolution of electromagnetic waves in curved space according to Einstein's equations is equivalent to the propagation of electromagnetic waves in a material medium described by the electric and magnetic susceptibilities that are allowed to vary in space."
Patsyk went on to say that this foundation gives "rise to the emulating effects such as gravitational lensing and Einstein's rings, gravitational blue shift or red shift, which we have studied in the past, and much more."
In other words, the techniques innovated through this experiment could help physicists more effectively study phenomena like gravitational lensing. The team is also exploring whether plasmonic beams (those that have plasma oscillations instead of light) could also be accelerated in curved space.